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shaped like a narrow U, and fitted on one end with a pipe B to admit gas, and on the other with a brass socket, C screw and plug with small opening through A scale D is fitted between the tubes and marked, as shown, with inches, and also with 1-10in. Water, usually coloured, is introduced by removing the cap C, until both sides are filled to the centre mark at 0, which is termed zero. Supposing the gas meeting surface of water at E, displaces it to 1, then the pressure is lin, or 10-10, and so on.-H. N. H.

[4757.)-GAS PRESSURE GAUGE. A gas pressure gauge is simply a siphon gauge described in "Mechanical Movements," p. 536, No. 298, but with water in lieu of mercury. Total height of pressure in inches is obtained by measurement between the level of water in the two legs of glass tube. Thus one inch up in one leg and one inch down in the other gives a pressure of two inches of gas, or air. The same simple instrument is also used as a "wind gauge," and was described in your pages [4757.]-GAS PRESSURE GAUGE is made in this manner. The plate up the centre is graduated in inches and the tube is glass bent up with a blowpipe. It is half filled with coloured water and one end is connected with the gas pipe by a piece of india-rubber tubing. The difference in level of water in the tubes gives the pressure of gas.-T. FLETCHER.

before.-C. D. C.

[4758.]-FRESHWATER FISH AND FISHING."Piscator" may be glad to hear that there is excellent fishing at the Crystal Palace. Within the last few days I have seen small perch and remarkably fine roach taken there in considerable numbers. It is said there are also carp, but it is now rather late for them to take a bait. The terms of subscription are, I believe, 1s. per day, 78. per month, or 21s. per annum.-H. J. PUCKLE.

[4758.]-FISHING.-Some very good fishing may be is about three miles from the Edgware-road Station on had at the Welsh Harp, Hendon, for a small fee. Hendon the North London Railway.-A. E.

[4759.]-POLISHING WALKING-STICKS.- French polish, i. e., shellac dissolved in methylated spirit, and applied with linen rag and a few drops of oil sufficient to prevent the rag sticking.-J. B. PRIMUS.

[4768.]-PLASTER OF PARIS.-To polish plaster of Paris castings, coat them with melted white wax, then place them before a fire until the wax is absorbed; a considerable polish can then be obtained by friction.

HARRY G. NEWTON.

[4768.] POLISHING PLASTER OF PARIS.Perhaps the following, which I extract from my notebook, may prove of service. Of stearine and Venetian soap, each two parts; pearlash, one; the stearine and soap cut small and mixed with thirty parts of solution of caustic potash, boiled for half an hour, stirring continually. Add the pearlash dissolved in a little rainwater and boil a few minutes; stir until cold, and mix with more ley until it is quite liquid; keep well covered ap. Remove all dust and stains from the plaster, and apply the wash as long as it is absorbed. When dry, rub with a soft leather or brush. Should the surface not shine, apply another coat. This recipe is in use about Hatton-garden.-LEATHER LANE.

[4770.]-FIXING PRINTS ON CARDBOARD.Flour-paste or gum-arabic, taking care in either case so to moisten the prints as to make them lie perfectly flat on their faces before applying them to the cardboard. Care must then be taken to press out all air-bubbles, lifting the print at the corners to free them if needful, and when this is done, and all paste, &c., carefully wiped from the edges of the print, cover it with a clean sheet of paper and put it under a slight pressure to keep it flat till dry.-J. B. PRIMUS.

-

CARDBOARD.

[4770.] FIXING PRINTS ON Ordinary bookbinders' or bill-posters' paste will no doubt answer "T. E.'s" purpose very well; or starch well boiled until, on cooling, it forms a jelly. The paste or starch should be evenly spread with a brush on the back of the print.-UNIT.

[4770.]-FIXING PRINTS ON CARDBOARD.Get about two tablespoonfuls of flour, with about a quarter pint water, and mix in a cup; then fill a saucepan half full of warm water, and put the mixture, in to boil on the fire, adding flour, and stirring round till thick. Put in a little alum.-A VOLUNTEER. [4771.]-FLUX FOR BRASS, GUN-METAL, &c.Flux used are parts of Copper Tin. Brass..

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The crucible or ladle should be lined with refractory
clay. If you pour oil on the flux when melted, it will
consume the dross and make it clear.-G. VALENTINE.
[4772.]-HERE BEER.-Procure an ounce of each of
the following:-Sweet gale, loz.; dandelion roots, 1oz.;
yarrow, loz.; agrimony, loz. If he wishes to have a
bitter beer let him add the following or any of them:-
Sanctuary, white horehound, wormwood, tansey,
quassia, bogbean, hops: boil the above in a covered
vessel for 20m. or 30m.; strain; add a suitable quantity
of cream of tartar; work with yeast in the usual way;
and when cool bottle for use.-JAMES BAGSWORTH.
[4773.]-CAUSE OF THE EARTH'S REVOLUTION.
-Your correspondent, "A Moke," is very far from being
a moke or donkey in asking the question which he pro-
pounds, Why the world revolves? It is easier asked than
answered.
If I remember right, it is neatly treated in
Brinkley's "Astronomy," which is the Irish college one.
Let us ask, Why does the moon revolve? We reply, be-
cause the earth does. The moon's rotation, though not
strictly on her axis, since she always shows us the same
face, is still circuitously axial, like as a man who shuffles
round you, looking at you, does really "turn on his
heel." The force of attraction not only operates on the
whole body of the orb, but also on its parts; and this

hold upon the parts is equivalent to a system of ties and
tags, or cogs of wheels, so that when the primary ball
turna, the satellite has to turn also. The whirl is en-
gendered amid the onward plunge, like as if you throw a
particoloured ball to a friend, you can see it spins on it-
self as it goes; so the moon turns, because the earth
turns as it wallows onward through the semi-vacuity of
space. But why does the earth revolve? For a similar
ong our orbit we revolve, because the sun's cogs of
reason we turn because the sun does. As we career
attraction impinge upon the earth's ribs like teeth, and
drag us round in our diurnal pirouette. It must be the
original projection which makes any of the secondary
spheres not turn the reverse way to the primary one.
Hence it would seem clear that the sun revolves be-
cause it also is in motion onward, round a centre of
gravity. My words are curt for brevity, not with any
dogmatism, which goodness knows I have no claim to
evince. I hope one of our chiefs will come out and fully
explain the interesting point, and I only wish that
("just to please me") he would try to do it without
algebra. My own (at least harmless) persuasion is that
the secret spring of the whole is in the oldest of dramas,
"The Book of Job," whose Hebrew is tole, he hangeth;
erets, the earth; al, upon; belima, nothing, xxvi. 7. In
"Isaiah" also (xi. 22) the hug or circle of the earth is
supposed to be a chariot in motion. What does a moving
firmament show but a living God? Who knows but, in
the style of Saturn's rings, the entire universe forins a
triple ring round that which is hidden by the veil of
blue, the throne of the Holy, Holy, Holy.-GIMEL.

[4778.]-CAUSE OF THE EARTH'S ROTATION.—
circumstance that his views of the laws of nature are
"A Moke's" difficulty arises from the not uncommon
taken from what he is conversant with on the earth's
surface, rather than from the principles which produce
the results which he sees. He forgets, therefore, or is
whether at rest or in motion, will continue in that state
not aware, that one of these laws is, that every' thing,
of rest or motion till that condition is altered by some
external force. Unless therefore some external force
checks the revolution of the earth, there is simply no
reason why, in obedience to this law, it should not con-
tinue to revolve. As it moves "in space," it is controlled
by no external force, except the sun's attraction, which
turns what would otherwise be its straight onward course
into an elliptical orbit, but in no wise affects its revolu-
tion on its axis. Motion, on the earth's surface, is always
affected by resistance of air and gravity, which draws
the body to the earth and there stops it by friction.
Here are, then, two external forces which do affect
here such as bodies have in space.-J. B. PRIMUS.
motion and prevent, therefore, any continuous motion

[4778.]-CAUSE OF THE EARTH'S REVOLUTION.
-When a body is set in motion it would, of course,
continue moving unless stopped by something. Now
there is nothing to stop the earth's rotation, except in-
deed the friction of the air (which turns with it) against
the ether which pervades space. Probably this has some
effect, but it is too small to be observed. By the bye, I
believe it has been thought that the tides may have some
influence on the earth's rotation. Perhaps Mr. R. A.
Proctor will be kind enough to favour me with his
opinion on this point, I am sure it would be read with in-
terest by many, as well as-BEACON LOUGH.

[4773.]-CAUSE OF THE EARTH'S REVOLUTION. -The cause of the earth's revolution is owing to its peculiar structure and gravity. As the earth is, no doubt, a, composition of meteors, it therefore is obvious it must retain its revolution as formerly. And further, I may state also that all planets are nothing else but meteors, but have cooled down to a certain temperature. And in reference to the earth as being once a meteor, it can be easily proved by there being fire in it.-A MANX

ΜΑΝ.

[4773.]-CAUSE OF THE EARTH'S REVOLUTION.
-If "A Moke" can understand the earth being set in
motion, surely he can also understand that by reason of
its suspension in space away from any opposing force,
there is absolutely nothing to prevent it revolving at the
same rate for ever, If he were to fasten a heavy ball to
a fine cord, and then spin it rapidly, he would find that
friction and gravition combined would soon cause it to
stop; but in the case of the earth, neither of these forces
are able to prevent its motion, by reason of their absence.
-HARRY G. NEWTON.

can obtain all information about the ailanthus by writ-
[4774.]-THE AILANTHUS.-" A Constant Reader"
ing to Dr. Wallace, Colchester, who supplies the eggs of
that and other kinds of silk-producing insects. The worm
is at this time of year in the pupa or chrysalis state.-
A. S. C.

[4775.]-LUMPS ON HORSES.-I should recommend
"A Groom" to bathe the lumps with a lotion, composed
of one, drachm of tincture of arnica in half a pint of
water, and the following ball may be given every night
for three or four nights successively, viz.:-Emetic
tartar, four drachms; assafoetida, four drachms; ginger,
two ounces; to be mixed and divided into four equal
balls, one to be given every oight. Food scalded, oats or
bran, mashes.-J. O. DYFFRYN.

[4776.]—LATHE.-The mandrel screw of my lathe (5in. centre) is 5-16in. diameter, and is cut with seven turns of Holtzapffel's No. 3 deep thread, 9:45 thread to the inch. These pitches were in use before the universal system of screwing on Whitworth's system was introduced. The maudrel noses of modern lathes are generally Whitworth's pitch, as affording readiness in getting taps cut and chucks fitted. The driving pulley is generally as large as will clear the base of the headstock.G. W. A.

[4779.]-HOLTZ'S ELECTRICAL MACHINE. — A
"Revenue Officer" will find the original machine fully
described and illustrated in Vol. III. of the ENGLISH
MECHANIC. Holtz's new machine is beautifully shown
and describled in a book entitled "Traité élémentaire
de Physique," par A. Privat Deschanel, to be had of

Hachette & Co., Charing-cross, price 103. G. W.
GRABHAM, M.D.

ammonium or dilute sulphuric acid outside the membrane. The title of sustaining battery is well maintained. They will give a distinct current for months; always of course, taking care that water is added, so that the salts do not dry up. I do not know if these are used for the "block signals," they are the only sustaining battery Iever heard of.—A. Ě.

[4782.]-TOMATO SAUCE-Put six large tomato's away the peel and core, beat them to a pulp, add quarter into a jar, cover down, bake in an oven until soft; take pint vinegar, one tablespoonful of mustard, a few cloves, palatable; boil all these together for about ten minutes. a blade or two of mace, one or two chilies, and salt until strain it, to the sauce then add as many finely-chopped shalots as agreeable, and boil again for ten minutes to finish. Bottle when cold.-M. S. B.

[4782.]-TOMATO SAUCE.-Take eight ripe tomatoes, four cloves, a little ginger, salt, pepper, and cayenne, and one small onion. Put all in an earthen jar on the stove until quite soft. Then run it through a sieve, and boil up with a little vinegar till it becomes as thick as cream. This is sufficient for four or five people, and is made the same day as used. It is excellent.-M. W. G.

[4782.]-TOMATO SAUCE.-Select them ripe and red, cut off the stalks, divide in halves and squeeze out the seeds, put in pan with a capsicum and a little gravy; add white pepper and salt, strain through cloth or sieve, and warm up. Or, to the above add sweet herbs, two onions stuck with cloves, strain, and add when warming a piece of butter rolled in flour. An addition is sometimes made of some lean ham minced fine, when the tomatoes are put in the stew-pan, also of taragon vinegar at the finish. To preserve tomatoes, bake in earthen jar until tender, pass through sieve, add to each four pounds one ounce of white pepper, one ounce of mace, a quarter pound finely-minced shalots, one ounce of garlic, half a consistency of good cream, put into small well corked pound of good glaze, boil together, add the juice of six lemons and strain. The whole should now be of the bottles and keep in dry place.-PATERFAMILIAS.

[This query has also been answered by Samuel Dison, "Quill-Pen," G. R. Fitt, and other correspondents.]

[4786.]-IMPRESSION OF FERN LEAF.-Sprinkle on a sheet of paper some powdered dragon's blood, lay the leaf face downwards upon it; by rubbing gently enough of the powder will be drawn up by the leaf to allow an impression being taken on moistened paper.HARRY G. NEWTON.

leaf in contact with "sensitive" paper in a photogra[4786.]-IMPRESSION OF FERN LEAF.-Place the phic pressure frame, and expose to light until the uncovered part of the paper becomes very dark; a beautiful print will thus be obtained, but it will require "toning and fixing" to render it permanent. The above method gives a light impression on a dark ground, but it may be reversed by using the print as a negative; thus any number of impressions may be obtained from one leaf.-W. KIMMIS.

[4786.]-IMPRESSION OF FERN LEAVES.-Prints from fern leaves, &c., may thus be taken: Take a sheet of stiff moderate thick and smooth brown paper, rub it over with oil, but not in excess, then smoke it by passing it over the smoky flame of a paraffine lamp or tallow candle, taking care to deposit the smoke evenly-this completes the preparation. Now lay the leaf on this smoked sheet, back or front, which way you wish the impression or print of, and subject it to gentle pressure by means of a sheet of paper laid over the leaf and stroked by the hand, as in using blotting paper. If it is a large leaf a cushion may be used to give the pressure. Next remove the leaf and lay it on a sheet of glazed or unglazed paper, which is to receive the print, pressing it down as before; remove the leaf and all is complete, and a beautiful print is the result, provided you have not shuffled the leaf about in the last operation. A faint outline may be obtained by using a little oil and smoke, and finish by painting the outline in proper colours. Such prints should be carefully handled until they are perfectly dry. In getting the skeletons of leaves much time may be saved by giving the leaves a slight boil before putting them aside to decompose, and if bleached by a solution of chloride of lime they should afterwards remain for half a day in a solution of sulphuric acid in water, as strong to the taste as weak vinegar, otherwise if the skeletons ever come into a destroy the fibre.-PEGASUS. damp situation after a while they will fall to pieces at the slightest touch, as the chlorine still continues to

[4787.]-SPEAKING TUBES.-The empty water-pipes of Paris were placed at the disposal of Biot, the great French philosopher, and though he spoke in a whisper, of three thousand yards.-A. E. his voice was distinctly heard at a distance of upwards

[4787.] SPEAKING TUBES. - Punch's "Colwell Hatchney" seems to have lost an inmate, who it seems has been diverting himself by putting down a "speaking or whispering tube" of galvanized iron (why galva nized?) 600ft. long and lin. bore! It seems the failure is looked on as a great bore; and after such a fiasco it is difficult to answer "Inquirer" when he asks to what iron, or any metal, is the worst material possible as to length is it possible to go!! However, badinage apart, acoustic qualities, for this purpose. known that gutta-percha possesses a singularly perfect It has long been material is, I should imagine, ever used now. A tube of adaptibility as a sound conductor; and no other whisper to the distance of 600ft. or more. In any large this material of to lin. bore will transmit even a town there are establishments where they are employed, and where "Inquirer" may see them in operation.GEO. ROBERT FITT.

[Is Mr. Fitt aware that gutta-percha soon decays, and particularly where it is exposed to light and air? When unexposed it is more enduring; and when at the bottom of the ocean it lasts for ages.-ED.]

[4789.]-MAP.-If "Map" would use paste made of

flour and water with a little alum in it he would find the map stick without the linen absorbing it.-A VOLUN

TEER.

[4789.]-MAP.-" Beriro" should well size his linen, and use paste instead of gum.-J. NASH.

[4781.]-SUSTAINING BATTERY.-A single cell of
Mullin's sustaining battery, consists of a narrow cylin
drical slip of sheet zinc, surrounding a copper vessel
closed at the bottom with wood, and a shelf provided at [4794.]-BATTERIES FOR MAGNETS.- The sul-
the top to carry crystals of the blue sulphate of copper.phate of lead battery would answer, subject, however, to
The copper vessel is enveloped with a membrane, and the objections inherent to it as mentioned. The descrip
the whole arrangement placed in a jar. Sulphate of tion of the magnet given is too vague for an exact
copper is used inside the membrane, and chloride of reply, as I cannot possibly tell what a 1 magues is,

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[4746.]-SCREW CUTTING.-In answer to Joseph, Moseley, it is a pity his screw has a square thread as that is not suitable for a split nut, unless a great deal of the thread is filed away towards both sides of each half of the nut. In Whitworth's lathes, which have a square thread rounded on the top, the nut only touches about of the circumference of the screw on each side or one half altogether, and the nut would not open or close without it." W. H. N.," on p. 331, Vol. X., gives a drawing of his clasp nut, on which I think mine, that I send herewith, is a great improvement. First, the square plate that carries the nut is held on by two screws and can be detached easily for cleaning, which should often be done. Next the cam, of which a front view is shown on Fig. A, instead of being outside the square plate with the pegs that actuate the half nuts coming through slots in the plate, is countersunk into the thickness of the plate on the inside, and the pegs are reduced in length. The nut is first made in one piece, and fitted into chamfer slides on the plate, one side being cast in the solid and planed out, and the other formed by a strip or wedge piece of wrought-iron, which is held on by two small screws, and bears on one side on the chamfer of nut, and is supported behind by an upright fillet also cast on the plate, as shown at A, Fig. 2. The nut is afterwards sawn in two. The cam is forged as a round plate, with a stalk to it like a mushroom-headed bolt, and is squared for the lever handle, and screwed on the end for a nut, by means of which it can be made to work as tight as may be desirable. The pins that work in the grooves of the cam are indicated in Figs. 2 and 3. I have shown the left-hand end of leading screw fitted into a socket with a bearing close to it, as recommended in my answer, (4681, p. 578), by which means it can be reversed so as to distribute wear. The section of bed shows the way have fitted my slide-rest to a bed of ordinary section the strips being of wrought-iron, about lin. broad x 5-16th thick, and about 14 or 15 inches long, the one over the clasp nut being forced up to its place by a wedge piece against a solid fillet B, Fig. 3, similar to the one in the nut. The other is set up by set screws C, as they can easily be got at on that side. There is also shown a stay bar that I put just under the end of mandrel head as there was no stay cast into the bed as there should have been. The slide-rest side view shows the one I use, except that I have added a fillet where the word is printed on the drawing, in order to enable the plate of slide to bear on its outside edges, as shown in the back view, Fig. 1, and not on the top where the double line is drawn, as I find this plan makes the slide-rest double as strong. I have shown the slide 10 long, and it would be all the better if it were 12in., the additional length being put on the right hand end. As to advice I think he would do best to put a clasp nut even on the square threaded screw, as the bevel wheels and clutch are troublesome to fit. It would be better to have the sides of his square thread sloped a trifle-but under any circumstances, to make quite sure first that the screw is exactly 48 to a foot, as screws are very often 39 or 481 to a foot, and with them you cannot cut screws to fit Whitworth's screw tackle. And if it proved not to be quite true, I should have it cut over again with a V thread which would probably involve reducing the diameter of the screw by 1-16in. You can cut your own nut, if you make a temporary one first by casting some Babbit's metal on to part of the screw which should first be well smoked over a paraffine lamp. Two or three threads quite enough.-J. K. P.

I

[4748.]-ELECTRO-MAGNETIC BATTERY.-I must apologize to "Beriro" for not having answered his query before, but I am afraid neither I nor any one else can efficiently aid him until he acquires a knowledge of the subject far greater than can be imparted in a short letter. The principle of magneto-electric machines may be thus illustrated:-Take a long insulated copper wire, say 200ft., and coil it upon a bar of soft round iron, say lin. diameter and 8in. long. Let the ends of the wire be connected with the binding screws of a galvanometer.

SCREW CUTTING.

Now take a strong bar-magnet and quickly approach one of its poles to within an eighth of an inch of one end of the soft iron, the needles of the galvanometer will move, indicating a current in a certain direction through the coil of wire: the needles will, however, again resume their original position, as the current is but momentary. Now take away the magnet, and the galvanometer will again indicate a current in the opposite direction to the first. The longer and thinner the wire the more powerful the magnet, and the more rapid its motion the more intense will be these induced currents. In most machines it is not the magnet which moves, but the coil of wire and its soft iron core. There are usually two coils and cores, which revolve rapidly in front of the poles of a horse-shoe magnet. It is evident that the current obtained is not continuous, but consists of a rapid succession of currents in opposite directions; if currents in one direction only are required, one set of currents are taken out of the circuit by a commutator arrangement. "Beriro" cannot, of course, make a machine from this description. I cannot give him details sufficient to do so without occupying too much space, and he will find them in most books on the subject, but I would not advise him to attempt it, as he is pretty certain to fail without full knowledge of the subject and considerable skill in construction of such instruments. Far better buy one if it will answer his purpose, but this I doubt, as for most uses of a galvanic battery a magneto-electric machine, unless very powerful and expensive, would be an inefficient substitute. If "Beriro" will say for what purpose he wants a battery I shall be happy to give him my opinion as to what will best suit him.-IGNORANT IRISHMAN.

[4750.]-CARBOLINE.-In reply to Mr. Jarman regarding the price, &c., of "carboline," I beg to refer him to my letter, No. 141 (page 448), in answer to the same question of "cheap gas" (page 383). Messrs. Woodward's price is 4s. 6d. per gallon.-C. D. C.

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[4753.]-GERANIUM PROPAGATION.-Take your cuttings and level them just under a joint (about four [4751]-TAPS AND DIES.-I thought "Semper Para-joints in the cutting are best, though you may strike tus" would bring down the criticism of some of "our" with only two), then having filled some 6in. pots with correspondents for his reply to this question. In order light soil put your cuttings in close to the side, all round about 3in. apart, two joints in and two out, and keep to produce a left-hand thread from right-hand dies, my opinion is the dies must be cut over a hob several damp. You will know when they are rooted by their depths of thread smaller than the blank, so as only to beginning to grow, then pot off in thumb pots, or let let the four corners touch it, and even then he can only them remain and pot at spring.-WELBY. hope just to strike the thread, which must be finished with the chasing tool. Altogether I should think it a very unsatisfactory method.-G. W. A.

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[4757.]-GAS PRESSURE GAUGE.-I send a rough sketch and description of the simplest form of a gas pressure gauge. They are made in various shapes and

סיייוייין ייין יייייי

sizes to suit requirements, but nearly all depend on the same principle as that I am going to describe-viz., displacing a column of water. A is a strong glass tube,

centre.

shaped like a narrow U, and fitted on one end with a pipe B to admit gas, and on the other with a brass socket, C screw and plug with small opening through A scale D is fitted between the tubes and marked, as shown, with inches, and also with 1-10in. Water, usually coloured, is introduced by removing the cap C, until both sides are filled to the centre mark at 0, which is termed zero. Supposing the gas meeting surface of water at E, displaces it to 1, then the pressure is lin, or 10-10, and so on.-H. N. H.

[4757.)-GAS PRESSURE GAUGE.-A gas pressure gauge is simply a siphon gauge described in "Mechanical Movements," p. 536, No. 298, but with water in lieu of mercury. Total height of pressure in inches is obtained by measurement between the level of water in the two legs of glass tube. Thus one inch up in one leg and one inch doen in the other gives a pressure of two inches of gas, or air. The same simple instrument is also used as a "wind gauge," and was described in your pages [4757.]-GAS PRESSURE GAUGE is made in this manner. The plate up the centre is graduated in inches and the tube is glass bent up with a blowpipe. It is half filled with coloured water and one end is connected with the gas pipe by a piece of india-rubber tubing. The difference in level of water in the tubes gives the pressure of gas.-T. FLETCHER.

before.-C. D. C.

[4758.]-FRESHWATER FISH AND FISHING."Piscator" may be glad to hear that there is excellent fishing at the Crystal Palace. Within the last few days I have seen small perch and remarkably fine roach taken there in considerable numbers. It is said there are also

carp, but it is now rather late for them to take a bait. The terms of subscription are, I believe, 1s. per day, 7s. per month, or 21s. per annum.-H. J. PUCKLE.

[4758.]-FISHING.-Some very good fishing may be had at the Welsh Harp, Hendon, for a small fee. Hendon is about three miles from the Edgware-road Station on the North London Railway.-A. E.

(4759.]-POLISHING WALKING-STICKS.— French polish, i. e., shellac dissolved in methylated spirit, and applied with linen rag and a few drops of oil sufficient to prevent the rag sticking.-J. B. PRIMUS.

-

[4768]-PLASTER OF PARIS.-To polish plaster of Paris castings, coat them with melted white wax, then place them before a fire until the wax is absorbed; a considerable polish can then be obtained by friction.HARRY G. NEWTON. [4768.] POLISHING PARIS.PLASTER OF Ferhaps the following, which I extract from my notebook, may prove of service. Of stearine and Venetian soap, each two parts; pearlash, one; the stearine and soap cut small and mixed with thirty parts of solution of caustic potash, boiled for half an hour, stirring continually. Add the pearlash dissolved in a little rainwater and boil a few minutes; stir until cold, and mix with more ley until it is quite liquid; keep well covered up. Remove all dust and stains from the plaster, and apply the wash as long as it is absorbed. When dry, rub with a soft leather or brush. Should the surface not shine, apply another coat. This recipe is in use about Hatton-garden.-LEATHER LANE.

[4770.]-FIXING PRINTS ON CARDBOARD.Flour-paste or gum-arabic, taking care in either case so to moisten the prints as to make them lie perfectly flat on their faces before applying them to the cardboard. Care must then be taken to press out all air-bubbles, lifting the print at the corners to free them if needful, and when this is done, and all paste, &c., carefully wiped from the edges of the print, cover it with a clean sheet of paper and put it under a slight pressure to keep it flat till dry.-J. B. PRIMUS. [4770.] FIXING PRINTS ON CARDBOARD.Ordinary bookbinders' or bill-posters' paste will no doubt answer T. E.'s" purpose very well; or starch well boiled until, on cooling, it forms a jelly. The paste or starch should be evenly spread with a brush on the back of the print.-UNIT.

[4770.] FIXING PRINTS ON CARDBOARD.Get about two tablespoonfuls of flour, with about a quarter pint water, and mix in a cup; then fill a saucepan half full of warm water, and put the mixture, in to boil on the fire, adding flour, and stirring round till thick. Put in a little alum.-A VOLUNTEER. [4771.]-FLUX FOR BRASS, GUN-METAL, &c.— Flux used are parts of Copper Tin. Zinc. Brass..

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Bell-metal for large bells.. small bells.. 16 The crucible or ladle should be lined with refractory clay. If you pour oil on the flux when melted, it will consume the dross and make it clear.-G. VALENTINE. [4772.]-HERE BEER.-Procure an ounce of each of the following:-Sweet gale, loz.; dandelion roots, loz.; yarrow, loz.; agrimony, 1oz. If he wishes to have a bitter beer let him add the following or any of them:Sanctuary, white horehound, wormwood, tansey, quassia, bogbean, hops: boil the above in a covered vessel for 20m. or 30m.; strain; add a suitable quantity of cream of tartar; work with yeast in the usual way; and when cool bottle for use.-JAMES BAGSWORTH. [4778.]-CAUSE OF THE EARTH'S REVOLUTION. -Your correspondent, "A Moke," is very far from being a moke or donkey in asking the question which he propounds, Why the world revolves? It is easier asked than answered. If I remember right, it is neatly treated in Brinkley's "Astronomy," which is the Irish college one. Let us ask, Why does the moon revolve? We reply, because the earth does. The moon's rotation, though not strictly on her axis, since she always shows us the same face, is still circuitously axial, like as a man who shuttles round you, looking at you, does really "turn on his heel." The force of attraction not only operates on the whole body of the orb, but also on its parts; and this

hold

upon the parts is equivalent to a system of ties and tags, or cogs of wheels, so that when the primary ball turn, the satellite has to turn also. The whirl is engendered amid the onward plunge, like as if you throw a particoloured ball to a friend, you can see it spins on itself as it goes; so the moon turns, because the earth turns as it wallows onward through the semi-vacuity of space. But why does the earth revolve? For a similar reason we turn because the sun does. As we career along our orbit we revolve, because the sun's cogs of attraction impinge upon the earth's ribs like teeth, and drag us round in our diurnal pirouette. It must be the original projection which makes any of the secondary spheres not turn the reverse way to the primary one. Hence it would seem clear that the sun revolves because it also is in motion onward, round a centre of gravity. My words are curt for brevity, not with any dogmatism, which goodness knows I have no claim to evince. I hope one of our chiefs will come out and fully explain the interesting point, and I only wish that ("just to please me") he would try to do it without algebra. My own (at least harmless) persuasion is that the secret spring of the whole is in the oldest of dramas, "The Book of Job," whose Hebrew is tole, he hangeth; erets, the earth; al, upon; belima, nothing, xxvi. 7. In "Isaiah" also (xi. 22) the hug or circle of the earth is supposed to be a chariot in motion. What does a moving firmament show but a living God? Who knows but, in the style of Saturn's rings, the entire universe forms a triple ring round that which is hidden by the veil of blue, the throne of the Holy, Holy, Holy.-GIMEL. [4778.]-CAUSE OF THE EARTH'S ROTATION.circumstance that his views of the laws of nature are "A Moke's" difficulty arises from the not uncommon taken from what he is conversant with on the earth's surface, rather than from the principles which produce the results which he sees. He forgets, therefore, or is not aware, that one of these laws is, that every thing, whether at rest or in motion, will continue in that state of rest or motion till that condition is altered by some external force. Unless therefore some external force checks the revolution of the earth, there is simply no reason why, in obedience to this law, it should not continue to revolve. As it moves "in space," it is controlled by no external force, except the sun's attraction, which turns what would otherwise be its straight onward course into an elliptical orbit, but in no wise affects its revolution on its axis. Motion, on the earth's surface, is always affected by resistance of air and gravity, which draws the body to the earth and there stops it by friction. Here are, then, two external forces which do affect here such as bodies have in space.-J. B. PRIMUS. motion and prevent, therefore, any continuous motion

[4773.]-CAUSE OF THE EARTH'S REVOLUTION. -When a body is set in motion it would, of course, continue moving unless stopped by something. Now there is nothing to stop the earth's rotation, except indeed the friction of the air (which turns with it) against the ether which pervades space. Probably this has some effect, but it is too small to be observed. By the bye, I believe it has been thought that the tides may have some influence on the earth's rotation. Perhaps Mr. R. A. Proctor will be kind enough to favour me with his opinion on this point, I am sure it would be read with interest by many, as well as-BEACON LOUGH.

[4773.]-CAUSE OF THE EARTH'S REVOLUTION. -The cause of the earth's revolution is owing to its peculiar structure and gravity. As the earth is, no doubt, a, composition of meteors, it therefore is obvious it must retain its revolution as formerly. And further, I may state also that all planets are nothing else but meteors, but have cooled down to a certain temperature. And in reference to the earth as being once a meteor, it can be easily proved by there being fire in it.-A MANX

MAN.

[4773.]-CAUSE OF THE EARTH'S REVOLUTION. -If "A Moke" can understand the earth being set in motion, surely he can also understand that by reason of its suspension in space away from any opposing force, there is absolutely nothing to prevent it revolving at the same rate for ever, If he were to fasten a heavy ball to a fine cord, and then spin it rapidly, he would find that friction and gravition combined would soon cause it to stop; but in the case of the earth, neither of these forces are able to prevent its motion, by reason of their absence. -HARRY G. NEWTON.

[4774.]-THE AILANTHUS.-" A Constant Reader" can obtain all information about the ailanthus by writing to Dr. Wallace, Colchester, who supplies the eggs of that and other kinds of silk-producing insects. The worm is at this time of year in the pupa or chrysalis state.A. S. C.

[4775.]-LUMPS ON HORSES.-I should recommend "A Groom" to bathe the lumps with a lotion, composed of one, drachm of tincture of arnica in half a pint of water, and the following ball may be given every night for three or four nights successively, viz.:-Emetic tartar, four drachms; assafoetida, four drachms; ginger, two ounces; to be mixed and divided into four equal balls, one to be given every night. Food scalded, oats or bran, mashes.-J. O. DYFFRYN.

[4776.]—LATHE.-The mandrel screw of my lathe (5in. centre) is 5-16in. diameter, and is cut with seven turns of Holtzapffel's No. 3 deep thread, 9:45 thread to the inch. These pitches were in use before the universal system of screwing on Whitworth's system was introduced. The mandrel noses of modern lathes are generally Whitworth's pitch, as affording readiness in getting taps cut and chucks fitted. The driving pulley is generally as large as will clear the base of the headstock.G. W. A.

[4779.]-HOLTZ'S ELECTRICAL MACHINE. — A "Revenue Officer" will find the original machine fully described and illustrated in Vol. III. of the ENGLISH MECHANIC. Holtz's new machine is beautifully shown and describled in a book entitled "Traité élementaire de Physique," par A. Privat Deschanel, to be had of Hachette & Co., Charing-cross, price 103.-G. W. GRABHAM, M.D.

[4781.]-SUSTAINING BATTERY.-A single cell of Mullin's sustaining battery, consists of a narrow cylin; drical slip of sheet zinc, surrounding a copper vessel closed at the bottom with wood, and a shelf provided at the top to carry crystals of the blue sulphate of copper. The copper vessel is enveloped with a membrane, and the whole arrangement placed in a jar. Sulphate of copper is used inside the membrane, and chloride of

ammonium or dilute sulphuric acid outside the membrane. The title of sustaining battery is well maintained. They will give a distinct current for months; always of course, taking care that water is added, so that the salts do not dry up. I do not know if these are used for the "block signals," they are the only sustaining battery I ever heard of.-A. Ě.

[4782.]-TOMATO SAUCE--Put six large tomato's into a jar, cover down, bake in an oven until soft; take away the peel and core, beat them to a pulp, add quarter pint vinegar, one tablespoonful of mustard, a few cloves, a blade or two of mace, one or two chilies, and salt until palatable; boil all these together for about ten minutes. strain it, to the sauce then add as many finely-chopped shalots as agreeable, and boil again for ten minutes to finish. Bottle when cold.-M. S. B.

[4782.]-TOMATO SAUCE.-Take eight ripe tomatoes, one small onion. Put all in an earthen jar on the stove four cloves, a little ginger, salt, pepper, and cayenne, and until quite soft. Then run it through a sieve, and boil up with a little vinegar till it becomes as thick as cream. This is sufficient for four or five people, and is made the same day as used. It is excellent.-M. W. G.

[4782.]-TOMATO SAUCE.-Select them ripe and red, cut off the stalks, divide in halves and squeeze out the seeds, put in pan with a capsicum and a little gravy; add white pepper and salt, strain through cloth or sieve, and warm up. Or, to the above add sweet herbs, two onions stuck with cloves, strain, and add when warming a piece of butter rolled in flour. An addition is sometimes made of some lean ham minced fine, when the tomatoes are put in the stew-pan, also of taragon vinegar until tender, pass through sieve, add to each four pounds at the finish. To preserve tomatoes, bake in earthen jar one ounce of white pepper, one ounce of mace, a quarter pound finely-minced shalots, one ounce of garlic, half a of good glaze, boil together, add the juice of six Fmons and strain. consistency of good cream, put into small well corked The whole should now be of the bottles and keep in dry place.-PATERFAMILIAS.

[This query has also been answered by Samuel Dison, "Quill-Pen," G. R. Fitt, and other correspondents.]

[4786.]-IMPRESSION OF FERN LEAF.-Sprinkle on a sheet of paper some powdered dragon's blood, lay the leaf face downwards upon it; by rubbing gently enough of the powder will be drawn up by the leaf to allow an impression being taken on moistened paper.HARRY G. NEWTON.

leaf in contact with "sensitive" paper in a photogra[4786.]-IMPRESSION OF FERN LEAF.-Place the phic pressure frame, and expose to light until the uncovered part of the paper becomes very dark; a beautiful print will thus be obtained, but it will require "toning and fixing" to render it permanent. The above method gives a light impression on a dark ground, but it may be reversed by using the print as a negative; thus any number of impressions may be obtained from one leaf.-W. KIMMIS.

[4786.]-IMPRESSION OF FERN LEAVES.-Prints from fern leaves, &c., may thus be taken: Take a sheet of stiff moderate thick and smooth brown paper, rub it over with oil, but not in excess, then smoke it by passing it over the smoky flame of a paraffine lamp or tallow candle, taking care to deposit the smoke evenly-this completes the preparation. Now lay the leaf on this smoked sheet, back or front, which way you wish the impression or print of, and subject it to gentle pressure by means of a sheet of paper laid over the leaf and stroked by the hand, as in using blotting paper. If it is a large leaf a cushion may be used to give the pressure. Next remove the leaf and lay it on a sheet of glazed or unglazed paper, which is to receive the print, pressing it down as before; remove the leaf and all is complete, and a beautiful print is the result, provided you have not shuffled the leaf about in the last operation. A faint outline may be obtained by using a little oil and smoke, and finish by painting the outline in proper colours. Such prints should be carefully handled until they are perfectly dry. In getting the skeletons of leaves much time may be saved by giving the leaves a slight boil before putting them aside to decompose, and if bleached by a solution of chloride of lime they should afterwards remain for half a day in a solution of sulphuric acid in water, as strong to the taste as weak vinegar, otherwise if the skeletons ever come into a damp situation after a while they will fall to pieces at the slightest touch, as the chlorine still continues to destroy the fibre.-PEGASUS.

[4787.]-SPEAKING TUBES.-The empty water-pipes of Paris were placed at the disposal of Biot, the great French philosopher, and though he spoke in a whisper, of three thousand yards.-A. E. his voice was distinctly heard at a distance of upwards

[4787.] SPEAKING TUBES. Punch's "Colwell Hatchney" seems to have lost an inmate, who it seems has been diverting himself by putting down a "speaking or whispering tube" of galvanized iron (why galva nized?) 600ft. long and lin. bore! It seems the failure is looked on as a great bore; and after such a fiasco it is difficult to answer "Inquirer" when he asks to what However, badinage apart, length is it possible to go?! iron, or any metal, is the worst material possible as to acoustic qualities, for this purpose. It has long been known that gutta-percha (possesses a singularly perfect material is, I should imagine, ever used now. A tube of adaptibility as a sound conductor; and no other this material of to lin. bore will transmit even a In any large whisper to the distance of 600ft. or more. town there are establishments where they are employed, and where "Inquirer" may see them in operation.GEO. ROBERT FITT.

[Is Mr. Fitt aware that gutta-percha soon decays, and particularly where it is exposed to light and air? When unexposed it is more enduring; and when at the bottom of the ocean it lasts for ages.-ED.]

[4789.]—MAP.-If "Map" would use paste made of flour and water with a little alum in it he would find the map stick without the linen absorbing it.-A VOLUN

TEER.

and use paste instead of gum. J. NASH. [4789.]-MAP.-" Beriro" should well size his linen,

[4794.]-BATTERIES FOR MAGNETS.- The sulphate of lead battery would answer, subject, however, to the objections inherent to it as mentioned. The description of the magnet given is too vague for an exact reply, as I cannot possibly tell what a 14 magu is.

but guessing at the meaning, I should say, yes. There are no "pint" cells of the improved battery; the principle involves large cells; and my remark as to the current yielded applies to the regular size in half-gallon jars. Made on a small scale, there would be too little surface to the negative element, and both power and constancy would be sacrificed. As to the coupling, a simple trial will tell best, as in my ignorance of the length of wire I cannot be sure. Probably two cells in series would be quite sufficient, and very likely one; and, therefore, the "quantity" coupling would be preferable.-SIGMA.

P. S. Since writing the above I learn that a misprint is the cause of my remark as to capacity of the cells, which should have been "8 three pint cells." These would suffice, but if by 6 convolutions is meant simply 6 single turns of wire, that would not be enough, and would be very bad economy. A length of wire should be used, giving resistance equal to that of the battery, an expla nation, which many will not perhaps understand, but which will be made perfectly clear at an early date. [4795.]-ENAMELLING SLATES.-The slate having been reduced to a perfectly level surface, a coating of colour, either red, green, or black, is applied according to the stone, it is intended to imitate. For black, Mander's tar varnish is sometimes used with good effect. The slab is then thoroughly baked in an oven heated from 130 to 250deg, from twelve to forty-eight hours according to size. The next operation is dipping. The colours, say grey and white, are then floated on to the surface of a cistern of water over which they float naturally into the shapes of the streaks of colour seen in marble. The slate, with its black ground, now burnt in, is "dipped" into the surface of the water receives from it the thin coat of colour. The slate again has to go into the oven, and when sufficiently hardened, a coating of enamel is applied. Another baking to harden the enamel and the slab is then vigorously pumiced to reduce it to a level surface. Baked again it is once more pumiced, and this time goes into the oven with the pumice wet on its surface. If necessary this last operation is repeated. The slab is then ready for polishing which is effected firstly by woollen cloths and fine sand, next by the finest and softest French merino, and lastly by the hand and powdered rotten-stone. The "dipping" process is not applicable to imitations of all stones. Some granites for instance are best imitated by splashing; others by splashing and sponging combined, while some have to be hand grained.-KAPPA.

you have a leading screw to the lathe-bed then
angle bracket to bolt on the place of the upper half of
you do not require a special slide rest, but only a right-
your slide rest, which is, in its turn, bolted to the upright
side of the said bracket. I will send soon a drawing of
part of my lathe which has a vertical slide of 19 in.
range. In this drawing the collar of slide screw is in-
side the groove in the casting, and is secured on the out-
side (top) by a pair of counter nuts. This slide should
fit on the outside edges, though it is not shown so in the
drawing.-J. K. P.

on this subject seems to be its own answer-How can he
[4818.]-PLANING MACHINE.-"Tometer's" query
fit up a planing machine when he does not know how
patterns are made? Answer-how can he ?-J. K. P.
[4816.]-CLEANING FURS-SABLE AND OTHERS.-

Thoroughly sprinkle every part with hot flour and sand
and well brush with a hard brush. Then heat with a
fully with a warm iron. For ermine use plaster of Paris
cane, comb it smooth with a wet comb and press care-
NASH.
instead of flour and sand, and treat in the same way.-J.
[4844.]-NUMISMATIC.-In answer to Mr. Samuel
Smith, I beg to give the following suggestions:-Procure
a piece of mahogany, size about 18in. by 12in., and one-
eighth or three-sixteenths of an inch thick, according to
Then with a carpenter's centre-bit drill holes of the re-
the thickness of the coins required to be exhibited.
quired size entirely through this board. These will form
another piece of mahogany of the same size, but only
the cells. For the bottom, screw on to the pierced board
one-eighth of an inch thick. If the coins are fine and
valuable, a piece of silk velvet may be glued upon the
bottom board before screwing it to the other. This will
appear through the drilled cells, and will form a smooth
surface for the coins to rest upon. When the coins are
arranged in their respective places, a small oblong label
below the cell for each coin. I do not mean the names
should be pasted on the upper mahogany board, just
to be placed under the coins, so that they have to be
below the cells themselves. When all the foregoing is
lifted up to show the labels; but on the upper board
completed, a sheet of glass, of the exact size of the board,
should be placed over all. It may be slid into grooves
in a neat edge fixed round the whole tray. This, I think,
and would be very safe if the glass was strongly fixed
would be a very serviceable manner of exhibiting coins,
into the edge. The only drawback is not being able to
follows:-Let the cells be pierced entirely through a
see both sides of the coins. This may be remedied as
piece of mahogany board, which is of the exact thickness
of the coins. Then fix a sheet of glass on each side, dis-
pensing with the second mahogany board.
turning the tray over, both sides of the coins may be
Thus by
seen. This latter mode, having much the appearance of
picture frames with glass back and front, is used for the
medals in the Sonth Kensington Museum. A number of
these frames are hinged vertically to a circular pillar,
and may be looked at and turned in the same manner as
the leaves of a book stood up on one end.
the above notes may be of some use to Mr. Smith.-
I hope that
HENRY W. HENFREY, M.N.S., &c., &c.

[4799.]-SCIENCE AND ART DEPARTMENT.-To obtain a medal it is necessary first to pass the elementary grade examination, and then the next or any subsequent year, to be one of the best half dozen or so who have passed first-class in the advanced stage. A selection of five or six of these is made by the examiner, and they have to undergo a further examination the same year. The best of these then gets the gold medal; the second best, a silver; and the two next a bronze cach. Medals are not given for the honours lexamination. I am not aware if any rule has been laid down as to whether one who has passed in honours can subsequently be examined in the advanced grade class examination of the same subject, and so obtain a medal. The only way of ascertaining is by letter to the Secre-says-viz., that he has tried to decompose water, neither tary.-IGNORANT IRISHMAN (A Gold Medallist). [4812]-VERTICAL SLIDE REST.-In answer to "Tometer "I send drawings of a vertical slide to bolt

to the top of an ordinary right-angle slide rest, only r that purpose the bracket should be stuckfon higher the back of the alde than shown in the drawing. If

[4845.]-ELECTROLYSIS.-If "Work" means what he

lyte at all, and if pure is not capable of electric de-
six nor 60 cells will do it; in fact, water is not an electro-
composition. If he means what is commonly called
decomposition of water, that is to say, sulphuric acid
dissolved in water, three Bunsen's cells willdo it freely
without the coil; but if he is using the secondary or
shocking current the "quantity" is so slight in this
that he would only produce a few microscopic bubbles
of gas.-SIGMA.

[4846.]-LOGARITHMS.-" Work" states the ques-
tion wrongly; or rather, the number given as answer
must be wrong. The decimal point ought to be six
places more to the right. As to working the example,
Work" should read the introduction which always ac-
companies every table of logs., and which instructs how
to use the column of differences.-J. K. P.

[4847.]-NATURAL FORCES.-The best writings on these subjects are scattered through many papers in the scientific periodicals and transactions; few of the text books go fairly into the principles. Grove's "Correlation of the Physical Forces" was the first work on the subject. Tyndall's "Heat as a Mode of Motion," worked out the idea for that force, and Balfour Stewart's "Elementary Treatise on Heat," and Cazin's excellent little work, "Phenomena of the Laws of Heat," are valuable contributions. Electricity remains yet in some confusion; even such a man as Tyndall feebly talks about the advantages of, for the present, working from the supposed two electricities, though admitting that there is probably no such a thing at all as electricity. One of my main objects in my papers is to clear this point up and give coherence to the vague views at present straggling about the scientific world. If "Thinker" has not read the earlier part of that series, commencing No. 242, I think the perusal might aid him; and, further, I wrote several papers expressly to make the correlation of the forces, and the most modern views of the subject comprehensible, and these papers might probably form a useful preparation for wider study. They are contained in Vol. X., pp. 58, 204, 288, 399, and 461; or in numbers 211, 217, 221, 226, and 229; but were not fully completed as they emerged into my present work, which engaged all my spare time.-SIGMA.

[4855.]-BATTERY CONNECTIONS.-The best way is to solder the upper edge of the platinum to a strip of copper, coating the solder and copper with paraffine to protect them from the acid.-SIGMA.

scopist would show "A. L. B." "how to do it" in five
minutes. Does he happen to know one ?-H. P.
made and exhibited in the following manner: Cat out
[4858.]-THAUMATROPE. - This amusing toy is
string as in the cut. Draw on one side of it a horse, and
a circular piece of card, to which fasten six bits of

a

jockey on the other (taking care to reverse the figures, or draw them upside down to each ot her); then, taking each hand, close to the card, twist or whirl it radidly one of the strings between the fore-finger and thumb of round, and, according to which pair of strings you use, you may cause the rider to appear upon, leaping under, or by the side of the horse, as you please.-OzOKERIT.

[4864.]-BATTERY FOR BLASTING.-No doubt the manganese battery would answer, as it would be required to work only at intervals, but six cells would not depend upon the distance to the point of explosion. I be anything like enough; the number needed would believe that Brunton's fuse, made from a copper wire away, explodes with least resistance, and that if enclosed in vulcanized rubber, and then partially cat platinum wire be used, it should be wrapped in a little gun cotton before insertion in the powder.-SIGMA.

Mammoth Theatre, Berwick-on-Tweed, is roofed with [4866.]-WATERPROOFING TIMBER ROOFS.-The down to the wood, and well tarred over; this is perfectly thin boards, covered with composite millboards nailed waterproof, and very durable. I understand the millboards were procured from a neighbouring mill, and did not come to more than 2d. per square yard.-J. LAMB.

beating seconds is 39-13929in. in length. To ascertain the length of any pendulum giving a required number [4869.]-LENGTH OF PENDULUM.-A pendalam of beats per minute use this formula

39-13929 x 602
x2

x being the number of beats required.

So in the query of " Electro-Magnet, No. 1,"
86-18922 x 602
a pendulum beating ninety times per minute, or one
17.39524 in. which is the length of
902
beat two-thirds of a second.-J. NASH.

QUERIES.

[4870.]-HARMONIUM CASE.-I have a large harstreaks have appeared nearly all over the surface. Can so to speak, that is, a number of rough patches and monium in walnut case, the polish of which is " rusting" polish again, short of French polishing, as I am no hand any friend tell me what I can apply to restore the at that? The draw stops in the above instrument are mahogany, covered with a coating of black varnish of some sort, very hard, giving the appearance of the tell me what this composition is, as I wish to coat two "stop" being made of solid black wood. Can any reader extra mahogany stops in a similar manner to correspond with those already in the instrument?-IVORY.

[4871.]-TRANSPARENT SIZE.-I will thank any of my fellow subscribers to inform me of the best sort of size to fasten gilt paper or tin-foil on glass; and as the gilt side of the paper is to be next the glass, the size must be clear and transparent, and such as not to tarnish the lustre of the paper or the foil, and at the same time cause either of them firmly to adhere.ELECTRO MAGNET, No. 1.

[4872.]-PRESERVING MUSHROOMS.-Will any reader tell me the best way to preserve button mushrooms so as to ensure their keeping during the winter and retaining their white colour ?-A MAN COOK.

exact mode of the black and white bronze given to gun [4873.]-BRONZING GUN BARRELS.-I want the barrels at the present time, to wit, the burning recipe black, if so, how the figure is brought out. I have the how long in, how often scratched per day if boiled till copper trough for boiling, and the lead tank for taking out; do pretty fair but not the exact thing; will some bright man give the particulars, and oblige ?-Tus

[graphic]

AMATEUR.

inform me the qualifications for the above situation? I [4874.]-BOILER INSPECTOR.-Would some reader am employed in the boiler making.-A HOLDERUP.

[4875.] ENTOMOLOGY. - AMERICAN MOTH TRAP.-Would some one kindly tell me what is the best form of cabinet for keeping moths and butterflies in? I cannot find it described in any of the books on Entomology, which have at various times been recommended in our journal. Also would some say whether they have found the American moth trap of any use. made one, and had it out several nights, but nothing ever seemed to come near it. Is it necessary to spread the sugar and treacle on a tree near it, in order to attract the moth in the first place? Any information will be most acceptable.-DERF ERRAC.

I have

[4876.]-COD-LIVER OIL.-Would some medical reader of the MECHANIC kindly answer the following questions? Whether cod-liver oil, which has been kept

place, is still a good remedy for weakness and loss of flesh, or whether its good qualities have become impared by so long keeping.-THE WIFE OF A SUBSCRI

BER.

[4856].-WENHAM'S PARABOLOID.-If this be fitted with an adjustable stop by which the light may be regulated, and be also capable of very varied focal adjust-for 7 or 8 years in pint bottles closely corked in a cool ments, there is no reason why it should not be used with the whole series of powers. But my querist can obtain a very good dark ground illumination by the aid of his mirror alone, if that be fitted so as to be capable of being thrown out of the axis of the instrument, the stage be there and the apperture thereof sufficiently large. I do not know that it is possible to tell "A. L. B." how to do this. A few trials will enable him to hit upon the right position of the mirror. He must bear in mind that no light must be thrown upon the lens, but just by one side of it. The object on the slide will refract a portion of the pencil and cause it to pass into the objective, carrying with it its message. Any micro

[4877.]-PORTABLE WINDMILL.-Will John James (reply 4612) kindly favour me with information as to wind mill for pumping! I want a means of keeping a cistern supplied at a convenient height, for domestic purposes, bath, watering garden, &c.-FRED. ROW, M.D.

and for the last two or three months have experienced & [4878.)-STIFFNESS OF FINGER. I am a violinist, painful and increasing stiffness of the first finger of left hand, especially about the knuckle joint, which has

naturally almost entirely prevented my playing on the instrument. If any of your numerous readers can suggest a remedy he will render me, and perhaps others similarly situated, a great service.-ROBERT HALL. [4579)-SECRET CODES.-I, in company with other of your readers, will be pleased to see a description of the instrument of" cryptographer," (page 595). Also any farther information of his plan that he may be willing to disclose, as I have failed to discover it.-ARGUS (4880.)-TO MILLERS-I have a pair of Derbyshire stones, 2ft. in diameter, also the spindle, which works in a brass in the bottom stone. It is 4ft. or 5ft. long, and has been driven from above. I have thought of fixing them to grind or kibble Indian corn, barley, or oats for cattle and pigs. I wish to ascertain how much work they will do? will it be worth the expense of fixing? and also, the best way of fixing to make them serviceable? At present I cannot see now the foot of the spindle can be lubricated. I think they have been originally fixed to grind paint. Informaating relative to the above will much oblige.

FARMER.

[4881)-CEMENT FOR SETTING STONES.-Can spy of your numerous readers inform me how to make a cement for setting stones? I have tried mastic and isinglass, and most of the cements sold to jewellers for the above purpose, but they will not stand hot water. any one can give me a good practical recipe I shall feel much obliged.-RUBY.

If

[48]-VIBRATING CONTACT BREAKER.-Will any of your readers inform me how many times in a second a nicely adjusted vibrating contact breaker can be made to vibrate and what determines the velocity?— ARGUS.

(4853]-MAGNETO-ELECTRIC MACHINE.-I have made a magneto-electric machine which I wish to attach to an electro-magnet, so that when the machine is in operation the electro-magnet will support about two ounces. I cannot get the machine to work, and I appeal to you for help. The electro-magnet is perfect; with a few galvanic cells it will support an armature of 5 or 6 ounces weight. The coils of the magneto-electric machine are also perfect, when I send a current through them the cores become magnetized. The insulation of the contact breakers is also perfect as I can send a galvanic current through them to the magneto-electric coils. I should state that my magnet is 10in. long, each pole 1țin. x fin. full, and is placed as close as possible to the cores, so as not to touch.-A. SUTHERLAND. [4884]-GRIFFIN'S GAS FURNACE.-I should be obliged if any one could give me any description of Mr. C. Griffin's gas furnace.-LEVER.

[4885.]-DISCOLORATION OF LEATHER.-I am obliged to Mr. Scholefield for his sketch of press. Mine are round, the largest being 4in. in diameter and 24in. deep, upon which is placed the leather; the ram, which is about ths of an inch smaller in diameter than press, is then put upon the leather and pressed down with 14in. screw. It will be seen that the pressure is very considerable, which I don't think any kind of wood (box ineladed) would stand for any length of time. I have painted the presses, and intend trying that. If it does not improve the colour, I must re-bore the presses and case them with brass, and perhaps a zinc ram would then remedy the difficulty. I should like very much to get some information on hardening, if any brother reader could oblige. Could I soak them in any chemical which would hasten the drying? The time of pressing occupies about a minute, and that they may get thoroughly hard I have to let them remain in the presses all night.

-G. A. G.

[4886.1-DYEING.-Can Mr. Young or any other reader inform me of the best way of dyeing woollen black when it has been bleached with sulphur ?-F. W. HUDDERS

FIELD.

[4887.]-DIATOMACEOUS EARTHS.-Can any of your numerous microscopic readers give me any information respecting the cleaning and preparing diatomaceous earths? I have been trying for a long time, and with very ill-success. I have this week been examining some of Topping and Barnett's preparations, and I am disgusted with my own efforts,-the last-named gentleman's slides being astonishingly beautiful. If any of your scientific readers can give me a hint as to the manipulation, I should be glad.-F. G.

[4888.]-STEREOTYPING.-I should be much obliged to" Amateur Stereotyper," who writes query No. 4784, if he would kindly say how he prepares his moulds of starch and whiting, and what success he has had with them. I should also be thankful to "George" (query No. 4742) if he will tell me how he obtains his music stereo, particularly if (as his query leads me to infer) the new process he speaks of is one which does away with the necessity of setting-up type. I am very much interested, as an amateur, in stereotyping, though hitherto I have met with indifferent success.-A CAMBRIDGE GRADUATE. (4889.]-HORIZONTAL WINDMILL. A question was asked some time back in your columns as to how Mr. Vallance proposed to stop or regulate his "horizontal windmill," described in No. 259, page 631, Vol. X., but I have not seen any satisfactory reply, which is much to be regretted, as the plan appears admirable; but as a fixture it requires a method of stopping which will ensure its safety in a gale. Mr. Vallance was not very clear on this point, and I am sure your readers would be much obliged if he would help us a little more.-C. D. C.

[4990.]-THE PAINTER OF SEVILLE.-Could any of your poetical and dramatic readers inform me where I can find the above poem in print? I have heard it given as a recitation, but have been unable to find the piece in any book as yet.-ELOCUTIONIST.

[4891.]-LONDON MATRICULATION EXAMINATION. I shall be glad if any of my fellow readers of the MECHANIC will tell me whether they consider Todhunter's Mechanics for Beginners" sufficient for the natural philosophy paper at the London Matriculation Examination; also what book or books they would recommend for the thorough getting up of the chemistry, English literature and French for the above examination.

—INQUIRER.

[4892.)-CHEMICAL ACTION ON LIMESTONE.-I have been collecting fossils in the limestone districts of Derbyshire, and amongst others I have found some limestone literally crammed with encrinite stems. In parts that have been exposed to the action of the atmosphere (or what is termed weathered) the limestone seems to have decayed and left the encrinite stems in bold

relief, they being more durable than the limestone. You will see at once that it is a dangerous undertaking to attempt to get good specimens, as we should have to climb high, which would endanger one's life. Now as I know some little about chemistry I thought it was possible to act on the limestone with some acid, and thereby produce the same effect chemically in a short space of time that it would take ages to accomplish by the action of the atmosphere. Consequently I made a soluto four of water, but it acted on the fossils as well as the tion of sulphuric acid and water, sulphuric acid one part limestone; I am rather inclined to think that the fossils contain fluorspar, for there was a piece of the limestone that was not covered with the solution, and it had the appearance of being acted on by fluoric acid, and it seemed to form a coating on the limestone that was in the solution. I should feel obliged to our chemical opinion as to how the atmosphere acts on the limestone friends of the ENGLISH MECHANIC if they would give their chemically, and whether in their opinion it is possible to act on the same with an acid.-ATOMIC.

[4893]-BRONZING CARD.-Will some correspondent kindly inform me how to bronze white card impressions off inetal dies? What kind of mixture is used to give a bright bronzed colour to the impressions?-B. T. [4894]-HEATED CHAMBER.-Will you or any of your correspondents inform me in what manner I can heat a room, or rather force a continuous current of air not less than 180, and the most economical way of doing it? I have a 4 horse-power boiler, and engine, and the room to be heated is 8 yards square. Any information on the above will be thankfully received.-A NEW

SUBSCRIBER.

[4895]-ELECTRICAL RESISTANCE.-Would some other of your electrical correspondents tell me what the BA unit of electrical resistance is exactly I knew that one was much wanted, but until lately did not know that such athing existed.-ZETA.

[4910.]-POROUS CELLS.-Which are the best to use the white or the red ?-Z.

[4911.]-ORGAN.-Will any practical reader give me an opinion? Is there any insurmountable barrier towards tuning reeds (fitted in a common harmonium pan) in unison with organ pipes, and will the same weight of wind do? I purpose conveying the wind by a branch, from the chimney leading from reservoir to windchest of or gan, and using the reeds with a second manual. The harmonium pan is fitted for two rows of reeds. What stops would give the softest tones? The organ has open diap., and principal (metal) stop diap., and clarabella (wood). Another wood stop (to be added) will complete the affair. I look with interest for an answer to "J. W.," 4659. I have thought of placing a sounding bor in contiguity to the reed pan. Has any reader tried the plan? and how does it stand affected supposing the whole requires muffling to hide buzzing? Does the conlatter. Will be delighted to see "Adept " on the boards tact of cloth with sounding box destroy the effect of the again. Unfortunately his letters ceased just as I became a subscriber.-A MERE NOVICE.

[As we have said before, the last time we heard from "Adept " he stated he was very unwell.-ED.]

[4912.]-CRACKED GLASS.-If a test tube, or any other glass used in chemistry, cracks from heat, an does not fall to pieces, is there any cement which will stick it sufficiently to use again in the flame of a lamp ? -QUILL-PEN.

[4913.]-ILLICIT STILL.-Would a still be called illicit which a person uses for making spirit for his lamp, or even to drink (please don't think I am going to), if he chose, so that he does not sell any ?-QUILL-PEN.

[4914.]-M. DELAURIER'S SINGLE-FLUID BATTERY.-Will some fellow-reader give me the details of this battery-how the solution of neutral chromate of soda and sulphuric acid is made and the elements used ?-R- N.

[4896]-SULPHATE OF MERCURY BATTERY.— TO " SIGMA."-I shall feel obliged by an answer to the following queries at your earliest convenience respecting the sulphate of mercury battery:-Is it necessary that the zinc and carbon should present a large surface? 2. Which should be the largest ? 3. How far should they be apart? 4. Should the carbon touch the bottom of the cell? 5. What would be the probable cost of sufficient sulphate of mercury to work four quart cells for working a small electric clock for twelve months? 6. What amount of attention does this form of battery require? 7. What are its failings, and what its advan- form me what this coin is ?-J. SEARR. tages, and lastly does it give off any kind of fumes?ALPHA.

[4915.]-SILVER COIN.-Can any correspondent in

[4897.]-GOLD LIQUID.-Will any brother reader be kind enough to inform me how the gold liquid is made, such as is sold in shilling bottles ?-EPPs.

[4898.] NEPTUNE.-It is stated in a popular periodical that Neptune is supposed to have a ring like Saturn. Would some one be so kind as to tell me what is known on this subject ?-R.

[4899.]-THE MOON.-Am I right in supposing that with a power of 300 the moon, whose apparent diameter in diameter in the heavens?-R. is about 30, would appear as if it covered a space 150

[4900]-CRAMP.-Would some correspondent oblige by informing me what is a good cure for cramp in the legs?-J. E. Y.

[4901.]-WATERPROOFING CALICO.-Can you inform me how to waterproof calico, and whether the same coating will answer for cementing two or more thicknesses of it together?-W. E. D.

[4902.]-VARIATION OF THE COMPASS.-Wishing to find what was the variation of the compass for this year at Greenwich, I searched in vain through several almanacs, &c., the "Nautical" included, but to my surprise could find it nowhere. Will any one tell me in what periodical it is published?-NORTH POLE.

[4903.]-VELOCIPEDE BOAT.-" Semper Paratus" would much oblige by giving a description of his mode of adapting the velocipede principle to a boat, as offered in No. 274, June 24, 1870, of ENGLISH MECHANIC (3973). CHEMICUS.

[4904.]-PISTON.-I have a direct-acting vertical engine making 80 revolutions per minute, the piston of the same, though nearly new, is becoming fluted, I use wire gauge packings; I have the least possible play between the slides; I do not press the packings hard. Will any of your kind readers please state the cause and remedy, and oblige-A YOUNG MAN.

[4605]-OLD MICROSCOPE.-Will "H. P." or some other microscopical correspondent kindly answer the following query? I have a very ancient microscope, made by Ross, some 40 or 50 years ago. Two of the objectives belonging to it are marked, 1-10in. and 1-12in. They are single lenses. Can they be adapted to an Oberhauser microscope, who could do it, and what would be the probable cost? At present they are useless, and only of interest in an antiquarian point of view.

-F.

[4906.]-PORTRAIT LENS.-Could any subscriber inform me what curves to grind the lenses for a combination portrait lens of in. or 6in. focus, or where I could procure a work on the manufacture of photographic leuses ?-J. I. B.

[4907.] - TANNING. - Would Mr. Geo. E. Davis kindly give me an easy and reliable process, with numerical and manipulative details for an amateur, for estimation of tanning in commercial articles, such as sumach, &c ?-Scio.

[4908.]-ENGINE VALVES.-Will Mr. Baskerville have the kindness to tell me if the cylinders and valves of stationary engines differ materially from those of locomotives, and whether the dimensions of the slide valve, steam ports, &c., given in his letter this week, are also applicable to a stationary horizontal engine ?-C. H. WYNNE.

[4909.]-INDIA-RUBBER WORKING.-I wish to meet with a work explaining the machinery required and the different processes india-rubber goes through in its preparation for covering cloth for waterproof garments? If any of your reader know of such a work or can give the information through your columns, I should feel much obliged. I think a good description in your paper would be very interesting to many of your readers, as the trade, so far, is looked upon as a great secret.-AUGUSTINE.

[4916.]-BRASS COIN.-Can some correspondent tell

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me what coin this is, and the value? and same size as engraving.-SAN SEBASTIAN. [4917.]-CHEMICAL NOTATION.-Will "Psi" kindly inform me where "The New and Old Notation of Chemistry" can be obtained ?-H. N. H.

[4918.]-BICHROMATE BATTERY.-Will "Sigma' kindly tell me in what number does he explain the method of fastening the copper to the carbon plates? Will a brass wire do as well to fasten to the zinc plate as a copper one ?-T. J. O'C.

[4919.]-LOWEST LINE OF PERPETUAL SNOW -Is there uniformity in the altitude of the line of perpetual snow on the peaks of mountains in the same latitude? On detached high peaks, like Teneriffe, it descends low for the latitude. On the Himalayas it is said that it descends lower on the southern side where the descent is abrupt than on the north where the descent is less perpendicular, and to an elevated extended table-land. The same thing is seen in America. Hood, and other peaks of the Cascade and Nevada range, The line of perpetual snow descends lower on Mount with its abrupt western slope, than on the peaks and ranges of the high table land of the Rocky Mountains. The temperature on the west sides of the great continents is milder than that on the east sides, or lower lands. Does that apply to the same degree at high altitudes?-SABBAS.

[4920.]-GEOMETRICAL PROBLEM.-The following was given last month at an examination in Germany. I To construct a shall feel obliged for the solution. triangle, given the bases, the differences of the squares of the two other sides, and the radius of the circumscribed circle.-JOHANN.

[4921.]-PHARMACEUTICAL PRODUCTS.-I wish to know the scientific names of the following:-Culver's root, Cancer plant, and Sweet Gum-all American denominations.-BERNARDIN.

[4922.]-ASIATIC COIN.-Will some numismatic

friend kindly describe the copper coin of which I send sketch (obv. and rev., are quite the same)?—THANKS.

[4923.]-MOTION OF WATER.-Will some obliging philosophical friend inform me and those readers of the ENGLISH MECHANIC who may take an interest in such a question, why water poured into a funnel invariably runs round in one direction as it runs ont, that direction being the same as the sun's course.-ZETETIC.

[4924.)-INSULATING.-"Sigma "stid last week that hc considered good paper saturated with parafine su

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