tains a mass of valuable information and formule for

many and different calculations, and describes various
slide rules. Then there is "The Slide Rule and its
Uses," by W. Gyngell, price 6d., a short and rather in-
complete work, as the price will indicate, and is prin-
cipally confined to instructions for screw cutting with
change wheels. Mr. T. Hailstone's little book I have
mentioned before, but it only applies to the inverted
slide rule used for timber, stone, or earth measurements.
-Q. YORKE.

[5135.1-REMOVING PLASTER OF PARIS.-You can use nothing safely except water, which will soften the surface, which you can then scrape off carefully. Wet the new surface and again scrape until you get it all off.-T. FLETCHER.

[5185.]-REMOVING PLASTER OF PARIS.-You can remove the plaster of Paris without injury by soaking in warm water for a few hours. The plaster will then easily part from the glass or brass; if not the first time repeat the process.-FORESTER.

[5185.1-REMOVING PLASTER OF PARIS.-Soak the article in water until the plaster becomes softened. This is a tedious but safe plan; is followed by silversmiths and others, whose goods are valuable, and found by myself to be the best where glass articles require unmounting, &c.-ENGRAVER.

[5187.] -SILVERED GAUZE BATTERY.-The gutta-percha shoe is easily made by softening the gum in boiling water, and moulding it on the zinc to the form required; the lead of the zinc should be made hot. I may say that while this battery has all the good qualities I ascribed to it, it has developed an unexpected bad quality. Electrotyed metals are porous to some extent, and it turns out that the silver deposit upon gauze is so to a degree sufficient to allow the acid to act through it on the copper below. I have long used such gauze for ordinary Smee cells with perfect satisfaction; but when left soaking for a considerable period, out of action, I found my liquid converted into a blue solution of sulphate of copper from this cause; this has led me to devise another modification, which so far seems devoid of fault.-SIGMA.

[5140.]-MECHANICS. - The best book science of Mechanics is Professor Willis's, price, about on tho 25s. It is, I believe, difficult to obtain.-W.

[5142.]-GALVANIC COIL.-The wire is not injured by previous use, except very slightly in conductivity, by the hardening due to two or three windings and bendings. The composition would greatly improve the coil. Either Smee, Daniell, or bichromate cells would suit, according to the amount of force desired. Of course the wires stated would produce a good coil for "shocking" purposes, but not what is called an "induction" coil, for the higher class of experiments on sparks, vacuum tubes, &c.-SIGMA.

[5143.]-REMOVING PHOTOS., ETC. FROM CARDS. -Soak the photos. in clean cold water until the parts separate. To remount, lay the damp photo., face downwards, on some blotting paper, and brush over it some starch paste (common starch made without wax grease), let it soak a minute or two, then put it on the new mount, taking care to press out all the bubbles carefully with a soft cloth made into a pad in the hand. -X. Y. Z.

or

[5147.]-FOCI OF ELLIPSE.-With an extremity of minor axis as centre, and half major axis as radius, describe an arc which will cut the major axis in the foci.-IRIOSAL.

[5147.]-FOCI OF ELLIPSE.-With the two axes defined, the foci are always found by merely striking, from the extremity of the axis minor as a centre, an arc whose radius is the semi-axis major. The sum of their two distances from this, or any point of the ellipse, is equal to the axis major.-E. L. G.

painted with Brunswick black, or a similar compound,
[5161.]-GLASS EMBOSSING.-The scrolls, &c., are
by the acid. Where large quantities are wanted stencil
on such parts as may be intended to be left untouched
plates are cut; if thin lines occur in the pattern they
point.-ENGRAVER.
can be cleared out with a metal, bone, or hard wood

[OCT. 21, 1870.

by increasing the size of the plates, or what is the same is no preventing the black deposit, which is caused by silver. There is no remedy; but the evil is diminished thing, the number of cells coupled for quantity. There impurities in the metal itself; it should be carefully brushed off before putting the plates away, as it causes great waste of zinc.-SIGMA.

ened a little by a modification of blowing, but in quick alter the position of the plug a little. See also if every [5170.]-FLUTE.-Examine the head of flute, and playing this would be impracticable.-IRIOSAL. key shuts airtight. Any note may be flattened or sharpdrive in a taper steel pin; if this comes lose he must fit drill a hole between the crank and the spindle, and [5171.]-BICYCLE TREADLE.-The best way for "One Who Don't Know" how to fix his crank on, is to must rivet it. I have seen them last a long time when done this way. I believe the best way to fix on bicycle a larger pin, if he can get the other one out, if not he cranks is to fit them on'square and rivet them; the manlike.-GEORGE F. S. square should project beyond the crank about of an inch, with the edges taken off, to make it look work

[5161.]-GLASS EMBOSSING.-The glass must be it. This done, a sharp-pointed instrument to scrape off the coated all over with Brunswick black, with a little white coating after the tracings left by the design; or if large wax mixed among it, and turps; a design pounced upon letters or ornaments, you must take pencil and Brunswick and write in the ornaments, if you wish the ground eaten away. Be careful to cover the glass well with the to be eaten away; vice versa, if you wish the letters to be coating, as the acid will find the smallest pin holes, and so prevent you doing the job neatly. Lay the glass flat, and put round the edge of the glass a quantity of wax to keep the acid from running over; if the acid is too specks of the same will rise to the top immediately on being touched with a feather when being examined; the strong it will break up the Brunswick black, and small weaker it is and the longer it takes to eat it away, the more security you have of good work. The fumes from the acid are very injurious to health if inhaled, therefore great care should be taken in using it.-mended by people who claim special merit as "practi

PAINTER.

[5164.]-MAGIC LANTERN PICTURES.-The gela-
the following manner:-A sheet of gelatine, such as is
tine slides to which "Sabbas" alludes are prepared in
engraving, and with a sharp steel point the lines of the I
used for tracing by engravers, is securely fixed over an
original are traced rather deeply on the transparent
substance. Lead pencil, or crayon dust, is then lightly
rubbed in with the finger, and the picture is ready for
glass, separated on three edges by a frame of thin card,
use. These pictures are held between two plates of
with paper pasted around the same edges.
means a cell is formed, and a succession of pictures can
By this
be readily exhibited.-SAUL RYMEA.

[5165.]-ZENTMAYER'S MECHANICAL FINGER.
The following is a description and sketch of this useful

deed whether any benefit whatever is derived from the addition of the salts named. I know they are recom[5172.]-ELECTROTYPING.-I am very doubtful in

carry weight, as practical people are very much given to cal;" but that sort of recommendation does not always makes an addition of this sort and does not spoil his attributing results to wrong causes; and if one of them think a little nitrate of copper may be an improvement, work, he is very apt indeed to call it an improvement. but that any advantage ever derived from the others is accidental, and due to weakening the current, which is much better regulated properly to its work on true not know the particular solution used in the case reprinciples than by such haphazard expedients. I do alkaline solution, such as the cyanide of copper, and ferred to, but a deposit upon steel must be made in an then, for economy, thickened by the usual process.SIGMA.

[5179.]-UNIVERSITY DEGREES.-A non-resident may compete for any of the degrees conferred by the University of London. tain a B.A. or, LL.B. degree, must first pass the Matricu "Inquirer," if he wishes to oblation Examination, held every January or June, The subjects for the first B.A. pass Arithmetic, algebra up to quadratic equations and loexamination are: garithms, geometry, Euclid, and analytical trigonometry, Latin, one prose and one verse author, English language, literature and history, and either French or German. In the second B.A., besides some of the above, statics, dynamics, hydraulics, pneumatics, optics, acoustics, astronomy, animal and logic and moral philosophy. For the first LL.B. physiology, 8 Greek author, examination:-Jurisprudence, Roman law with Latin translation, and the Constitutional Law of England. For the second LL.B. examination :-Common law, equity, real property law, law and principles of evidence, and Roman law. For further particulars "Inquirer' would do well to get the "London Calendar," price 4s, where he would find all the papers set for examination for the year.-OXONIENSIS.

accessory to the microscope :-A is the top plate of the I would suggest is this. Get an illustrated catalogue mechanical stage, the circular plate being omitted. from one of the makers and select his type of stand, and [5181.]-MICROSCOPE.-" R. T." might, I think, purchase his lenses and make his own stands. The plan tube, wide enough to admit illumination from the mirror. articles on the microscope, I have spoken of the essenThe cap B is fitted to the lower body below the stage; then set to work. His work must be good, and all the sub-stage C is fastened into the cap by a narrow parts must be firmly put together. In one of my D is the clamp by which the finger is attached to the tials of a good stand, and "R. T.," I think will be able stage by means of the screw E. A steel cylinder G is by the aid of those remarks, and a good cut of a nicely fitted into the top and bottom of the tube F, leaving room inside for a light spring to press the steel The cost of his eyepieces A and B, will be about 10s. each. "Student's" stand, to manage the mechanical work. [5150].-LATHE QUERIES.-An ordinary point tool provided at H with a steel pin, accurately fitted into the Mirror, (say) 78. 6d. Any optician will sell him the cylinder upwards. To prevent turning, the spring J is Lenses, 1", 12s. to 20s.; ", 17s. upwards; ", 20s. to 50s. placed so as to cut horizonally to mark divisions. I explained this about ten months ago in the ENGLISH MEfork at the top of the tube F. By turning the nut K, lenses. Perhaps Mr. Collins would be as good a one as CHANIC, in the matter of dividing a segment of slide-justment to the needle N in case the finger is to be atthe spring J is elevated and depressed, giving nice ad- any for his particular case.-H. P. rest. I used to splice my bands as sailors do a threestrand rope, but have given it up in favour of hooks the cap B, to bring the end of the hair and the object tached to a microscope not having rack movement to vegetable impurities as possible.-IRIOSAL. and eyes. I never find them jerk off if they are not a [5182.]-CEMENT.-Use lime with sand, as free from great deal too big. The small end of the hook should be in close approximation. The end of the spring J forms of the same size as the new gut, which should be pared fastened by wrapping gum paper around. Turning the posited in small crystals. Another method consists in a little ring, with a screw cut inside, into which a cork copper is really a suboxide, Cu2O. [5183.-PROTOXIDE OF COPPER.-The red oxide of carefully with a penknife and made blunt-coned at the M is screwed to receive a needle N, to which a hair is pared by boiling verdigris with sugar, when it is deend, and screwed hard in with tallow (not water), plenty inclination. A slight pressure on the button L brings mixed with a large excess of ammo i, and warming the It may be preof it; and I think not seared with hot wire afterwards, down the hair, and the spring inside of F instantly lifts mixture in a vessel completely excluded from air, when cork facilitates the adjustment of the hair to the proper digesting copper foil in a solution of cupric sulphate, though this is advocated generally. The best form of peg is one that fits the holes, if the holes are drilled it again when the pressure is removed. The tube Fit is deposited as a reddish-yellow p taper, which is the best plan; and I don't like them much less than 1-20in. diameter, and nearly as much solid turns in the clamp D in order to adjust the hair and be prepared by igniting three part of powdered upric left between the most crowded ones. Make the peg as cork more conveniently, and when brought back again oxide (black oxide) with four parts of copper filings in der. It may also short as you can work with. It should be hardened for which gives the vertical motion. When the apparatus copper is generally called the protoxide, the red oxide it is tightened by a set screw. Only one movement is a covered crucible.-OXONIENSIS. rigidity and lasting power, and tempered for strength, is to be used, the material to select from is placed on being called the suboxide or cuprous oxide. It may be added to the microscope stand by this instrument, that say to a spring temper-i.e., blazed off. I have not had the sub-stage C and focussed, then the point of the prepared by boiling a solution of cupric sulphate (blue [5188.]-PROTOXIDE OF COPPER-Black oxide of time to make, or, rather, I have had no immediate want of the coming model peg, so it is at present in the by means of the stage movements and turning of D; tash) and sugar for some time; the oxide precipitates as embryo state.-J. K. P. hair is approximately brought over the selected object almost in the same plane with the object. vitriol) with solution of potassic hydrate (caustic pothis brings the hair nearly in focus too, because it is adjust the hair precisely over the selected shell, press covered crucible.-CHEMICAL. a red powder. Or to 79 parts black oxide copper, add Next 63 parts copper turnings, and heat to low redness in down the button L, and the shell will adhere to the [5154.]-ARTIFICIAL FUEL.-I buy mine at the oil-substitute a glass slide moistened by breathing on it, hair. Now remove the slide with the material and shops, in bricks weighing fully five pounds each, at the retail price of 78. per hundred. I find them exceedingly useful, and am told that they are composed of coalust, cemented together by potato starch, and compressed in an iron mould.-PATERFAMILIAS.

[5152.]-CONDENSER.-The price will vary with the style of fitting, but one suitable for a " Student's microscope" may be obtained from any optician for about 20s. -H. P.

(5156.]-HARD SOLDER FOR GOLD.-Put a small

quantity of zinc in your solder and try it again.-T.

FLETCHER.

[5158.] - BIRDLIME.-Boil olive oil until you can draw out a piece as big as a pea, say 2ft. long.-FIRST ANSWER.

and having brought it into proper position, push down
the button L again, and the shell will be deposited on
the glass slide.-J. S. M.

[5166 & 5190.]-GRIFFITH'S GAS FURNACE.-The
perforated cylinder is made of fire-brick, or, at a little
fire-clay or plumbago ones, and are generally provided
exra cost, plumbago; the crucibles used are the usual
with covers, which, however, are no more essential in
opening d allows a fresh entry for air, which is partly
this than in any other furnace; the bottoms of the burn-
ers should be open to allow free access of air, and the
warmed by passing up among the tubes; and the final
support and the body of the furnace. The dimensions,
air supply is derived from a small space between the
laboratory purposes than for general metallurgy; but no
as at present made, are of small size, adapted rather to
doubt on application the makers would furnish all these
particulars, and deliver sizes suited to the work required.

[5158.]-BIRDLIME.-Take any quantity of linseed oil, put it into an old pot, or any vessel that will stand the fire without breaking; the vessel must not be more than one-third full; put it on a slow fire, stir it occasionally until it thickens as much as required. This will be known by putting the stick in water and trying it with the fingers. It is best to make it rather harder-SIGMA. than for use. Then pour it into cold water. It can be brought back to the consistency required with a little Archangel tar.-C. R. F.

less than half its original power after very short action,
[5167.]-BATTERY-Smee's cell invariably falls to
owing to the adherence of gas to the surface of the

dently too soft. Harden with rosin. If you polish with
putty powder face the pitch tool with with a nice close and
[5184.]-ACHROMATIC LENS.-" A. B. C." (p. 94),
your tools and emery are right, but your pitch is evi-
even piece of cloth. It will probably take about 5 hours
pitch with rouge (washed of course); it should then take
with putty powder. I should advise you to polish from the
you not more than three hours for each surface at most.
from the fine emery, sufficient just to reflect the light of
The glass should have a semi-polish upon it when left
a window at an angle of 45°.-EDMUND M. T. TYDEMAN.

it (hydrate of lime) is the best known purifying agent for
[5186.]-GAS.-Lime made sufficiently moist that a
coal gas. The tests for impurities in coal gas are-Acetate
mass squeezed in the hand will retain the shape thus given
of white writing paper is blackened on being held over
of lead in solution, which, when smeared on a piece
reddened if carbonic acid be present; turmeric paper,
also moistened, which is turned a reddish-brown if am-
a stream of coal gas if sulphuretted hydrogen be present;
blue litmus paper, which, when moistened with water, is
in the form of small books; they are exceedingly con-
monia be present. Test papers of acetate of lead, tur-
meric or litmus are to be purchased at most chemists,
venient, and no works should be without them.-R. R. C.

[5186.]-GAS.-The most important impurities of coal gas are ammonia, sulphuretted hydrogen, and carbonic acid. Ammonia may be detected by placing a piece of moist reddened litmus paper in the jet, the ammonia, if present, will turn it blue. A piece of paper steeped in a solution of sugar of lead, and held in the jet, will be turned black if sulphuretted hydrogen is present. If the gas be passed through limewater, the carbonic acid will cause a white precipitate of lime. Besides the lime purifier, the gas is passed through condensers to deposit the tar, and then through a "scrubber," an iron box fitted with perforated shelves, on which are laid small pieces of coke over which water is made to trickle, so as to absorb the ammonia out of the gas as it ascends through the box.--OXONIENSIS.

[5187.]-EBONITE ELECTRICAL MACHINE. The woodwork ought to be well baked and inade nearly non-conducting, and there should be only enough to support the working parts. Two pairs of rubbers, &c., are

decidedly preferable to one. For medical uses, no higher

insulation is needed in the coil as described and now

referred to. High insulation is needed only where great intensity is to be developed.-SIGMA.

[5188.]-BLACK FOR BLACKBOARD.-"Blackpot" should first paint his board with ordinary black paint, such as will dry with a gloss; he should then apply a coat of black paint, mixed with turps instead of oil, which will dry a dead black. N. B.-The flatting, or last coat mentioned, should be mixed by an experienced hand.WEDNESBURY.

[5188.1-BLACK FOR BLACKBOARD.-A recipe has been given in a back volume of the ENGLISH MECHANIC, but I cannot refer to the page, &c., just at present. I have tried it and found it answer much better than paint. Take lb. of logwood, and sufficient boiling water to cover it; allow it to stand for 24 hours. Strain, and apply the solution, boiling if possible, a couple of times, allowing the board to dry in the interval. Then dissolve 4lb. of copperas in about 1 pint of boiling water, and apply it boiling, once or twice, according to the degree of blackness obtained. Before using it, rub it over well with rushes, straw, or ferns. A correspondent suggested that the board should be well rubbed over with shoemakers' heel-ball. I did not use it. I found it difficult to rub the chalk off at first, but after a fortnight's use I experienced no difficulty. It is the best blackboard I have in school. I use unprepared chalk, which writes well.-SCHOOLBOY II., Pontardawe.

(5189.]-EYEPIECE OF TELESCOPE.-I will attend to Grateful" when I have leisure to write a treatise upon the subject he requires. It would be impossible to make everything clear within the limits of a letter or two.-EDMUND M. T. TYDEMAN.

[5194.]-PHOTOGRAPHIC.-If " Paddy" will proceed as follows I think his troubles will end:-Dissolve the nitrate of silver in the proper amount of distilled water. Do not use either rain water or water condensed from an engine. Next dissolve a grain of iodide of potassium in a few drops of water, and add it to the bath. Shake well, and filter after it has stood a little. Add a few drops of glacial acetic acid, and the bath will be ready for 11 30.-W.

5194]-PHOTOGRAPHIC.-Let "Paddy" try the following formula for nitrate bath :-Re-crystallized and raeutral nitrate of silver, 200 grains; distilled water, 10 uid oz.; add 1 drop of nitric acid for each 10 ozs. of solution. Dissolve and filter. Pour into the bath, and then clean a plate (one about 5 x 4), coat with collodion, And let it remain in the bath some time, so that all the iodide of silver, which is at first formed, is dissolved out by the nitrate. It may take from 20 to 30 minutes before the glass becomes again nearly transparent. The bath is then fit for use.-FRETWORK.

and wax in it. If the carbon plates are ever removed
from the acid they only require washing or soaking in
water.-SIGMA.

[5226.]-FROSTING SILVER-I have an old recipe
for the above, but I cannot answer for its being good for
"H. P. S.'s" purpose; it is also rather vague in its di-
rections:-Put a few drops of muriatic acid into a little
water in a wineglass; apply with a camel-hair brush to
the article to be frosted.-X. Y. Z.

[5226.] FROSTING SILVER.-Put some alum into a copper vessel with some water; put it on the fire until it is dissolved; wash the article to free it from grease, and put it in and boil it well until it is white; wash in clear water and whiting.-Proved.-DENTAL,

(5228.)-WELSH PRONUNCIATION.-"Kelt" should pression of Celtic sounds by means of English letterget a Welshman to pronounce in his hearing; the excombinations being difficult. For instance, how can I

explain the Scottish sound of "loch" to an English

man ?-IRIOSAL.

occasional fresh amalgamation in all forms of cell,
[5231.] - ZINCS IN BATTERIES.-They require
and it should be done just after use, first cleaning well.
-SIGMA.

[5232.]-PLATINIZING SILVER.-R. T. Bell is not wrong. I am naturally of a refractory disposition, and If he places me in a small quantity of aqua regia or nitro-muriatic acid, and keeps me in a warm place a few days, I am sure to fal, by the acid turning red. As soon as I have dissolved, dissolve. He can always tell that he is being successlet him evaporate the liquid at a gentle heat until it is nitric, and muriatic acids). Add a little water and I am as thick as honey (so as to get rid of the excess of the ready for use. A dozen drops of this solution goes a long way in platinizing silver. The operation is performed in a small glass or beaker, covered with a watch-glass to keep in the fumes, and placed in a little sand in a saucer, to equalize the heat. May I trouble your readers to call me by my right name.-PLATINUM.

am not to be dissolved in a minute.

[5232.]-PLATNIZING SILVER.-R. T. Bell is mistaken. The red colour shows platinum is dissolved; as large surface as possible is desirable, such as thin foil and great heat is quite unnecessary, as it wastes the acid. A prolonged digestion at a moderate heat is best.SIGMA.

[5237.]-CARTE DE VISITE.-If "Imowole" prints on plain paper, and after fixing and washing puts them drying varnish the back with a solution of gum dammar, in boiling water about six or eight times, and after 25 grains, Benzole loz., he will find the colour take well.-FRETWORK.

QUERIES.

[5247.1-COPYING PAPER.-Can any one give me a good recipe for making the black copying paper used in "Manifold Writers," and oblige-TELEGRAPHIST.

[5248.]-THE RIPENING OF PEARS.-Why do pears ripen quicker hanging up than laying down ?-P. B. [5249.]-VARNISH FOR CLAY PIPES.-Will some brother reader inform me of a varnish for clay pipes, coloured (by sinoking), that will give a polished appearance to the pipe and not taste when smoked?-F. G. C. following passage from an account of Savart's researches [5250.]-THE VIOLIN.-Will some reader explain the on the violin ?--"In order to obtain the true sounds of the back and belly, these pieces were placed in a vice, between two bits of cork shaped like a cone, at a point longitudinal, crossed each other. This was ascertained where two nodal lines, one transversal and the other in the usual way, by sprinkling the surface with very fine sand, and putting the pieces into vibration with a violin bow applied to the edges; and the same nodal system being produced in each the relative difference of pitch was easily found by means of the bow." is a nodal line, or a nodal system ?—R. T.

What

[5251.]-PATTERN ON LINEN.-I want to put a the pattern is marked by fine perforations. A powder is pattern on white linen by means of a card, on which rubbed through the holes and leaves the pattern on the cloth underneath. Could any reader say what powder would suit, and the method of sticking it or fastening to the cloth so that it would not easily rub off?-W. Y.

[5252.]-WATER POWER.-Would some reader give me the following information? What is the horsepower of the water in the under-mentioned stream, and what would be the best wheel or wheels to erect, with size of shaft for water wheel and first motion ? Width height of fall, 201t. The above water is running to of river, 45ft.; depth, 3ft.; speed per minute, 111ft.; wasto near a large city and great trading mart.-A. HOBSON.

[5253.]-SILVER COIN.-Will Mr. Henfrey, or some other numismatic reader, kindly inform me what the

The

following soin is ? Silver; size of a sterling penny. Obv.: Enricus, and the letters J. R. R. A., within circle. having an open centre, enclosing a pellet, with a pellet four letters are placed feet together forming a cross in each angle. Rev. Bo. no. ni. Letter A with four pellets within inner circle M.M. cross patee. Weighs 21 grains. Query, is it a penny of St. Edmundsbury or an Anglo-Gallic Denies of Henry II. ?-DELTA.

[5254.]-PARCHMENT SIZE.-Can anything be put into parchment size to prevent it from turning off, and what; it being useless, as well as offensive to the olfactory nerves in that condition ?-ROBINSON CRUSOE.

[5210.]-REFRIGERATION.-It is said that 133 parts of sulpho-cyanide of ammonium, with 100 of water, will [5255.]-HEATING BY HOT AIR.-What is the best reduce the temperature of the water 12 to 18 below and cheapest work written on heating buildings by zero(Centigrade); and 150partsjof sulpho-cyanide of potas-hot-air, not hot-water pipes?-ONE IN A FIX. sium, with 100 of water, will reduce the temperature 10 to 24 below zero. The salts are to be finely powdered, and stirred with a glass rod in a glass vessel, covered with cotton wool. Is there any easy method of applying this process to ordinary household purposes?-H. J. P.

[5241.]-GILDING SILVER CHAIN.-Can any correspondent tell me the cause of failure in attempting to gild an ordinary silver link chain? I dissolved 15 grs. of chloride gold in excess of cyanide of potassium, making [5200.]—CUTTING SCREW-THREAD IN LATHE.-- 4oz. of solution, and heated it to nearly boiling; threaded I do not know of any rule. The tool-point must be a the chain upon a piece of silver wire, suspended it in counterpart of the intended thread. Whitworth's are the solution, and attached the wire to the zine end of of 55 point angle, rounded off equally at top and bottom, two cells of a Grove's battery, corrected for quantity, till the thread is in depth of what it would have been each zinc 12in. by Gin., attaching a piece of gold to the if not rounded at all. I use a gauge or bevel of 224, platina pole of the battery about the size of half-a-crown and apply it to both sides of the square shaft of the piece, after leaving the chain in the solution half an tol to see that the thread is upright, and I hold the tool hour there was no sign of gold, and I then immersed while grinding it on a block of wood laid flat on the the chain in the solution about an inch at a time, when grindstone frame, and alter the thickness of this block in a minute it was coated. After so treating the whole for the two sides of the tool, so as to bevel one side of the chain I again threaded it upon the wire and immore than the other underneath, for a right or left-mersed it as before, when in less than two minutes it handed screw as wanted. A bead tool is required to "top" was nearly plain silver again. I managed to plate it the thread.-J. K. P. small pieces at a time, but that is a very tedious job.W. RYAN.

[5204.]-INDIAN COINS.-"C. G. W."-Eight pice is the 24th part of a rupee. The rupee is equal to about two shillings sterling, and is divided into 16 annas (copper) and each anna into 12 pice. I am not acquainted with the term "chuckrum."-D. T. BATTY.

[5214.]-PAIN IN THE LEG.-I would advise James Lewis to try the Turkish baths, and give the shampooer special instructions to manipulate the part affected. If he does so I should like (through your columns) to hear the result, as I am particularly interested in those baths, having taken them regularly for about 12 years, and have great confidence in them.-D. T. BATTY, [5216.] CRUCIBLE FOR MELTING BRASS.RP." can obtain fireclay crucibles at Griffin's, Garrickstreet, Covent-garden, W. C., for 6d. a dozen. I do not know what size they are. Both ends are left open might be closed for a draught.-CUTHBERT. F5217.]-BICYCLE CRANK.-"W. G. C." (page 35) will find the best length for all sorts of roads is 6in.; for speed on good roads, 5in. I can get up moderate hills with a 5in.-GEORGE F. S.

one

[5242.]-SILKWORMS.-In the fourth paragraph of
"Saul Rymea's" letter (501, p. 63, No. 3 of present volume
of ENGLISH MECHANIC), he speaks of a silkworm recently
introduced from Japan (Bombyx Yama-mai), which feeds
on oak trees. I should like to know whether this is the
same silkworm the cocoons of which were said to be had
in great quantity about a year ago, because it was then
said that on account of the worm feeding on oak trees the
gam was not so readily removable as that of the mul-
berry, and not at all by the same means. I happen to
know that some spoiled cocoons went the round of the
silk mills a little over a year ago, for the purpose of
ascertaining whether a marketable article could be pro-
duced from it, and that in one or more instances it was
I obtained a little,
pronounced against as not suitable. I
and readily removed the gum, so that it would take a
dye beautifully, but still it was said at the mill that it
would not work as well as the other. I should like to
ask "Saul Rymea," or any one who will take the trouble
to answer the question if he knows whether these diffi-
culties with regard to the produce of the oak-feeding
silkworm still exist ?-SILKWORM.

[5217.]-BICYCLE CRANK.-The greater the throw of the crank the easier the bicycle will be to work. This [5243.] RUPTURED FEED PIPE.-Would any fs, of course, only true within reasonable limits, as it is reader inform me if there is any method other than by a labour of itself to move the legs round a large circle. hand of lapping a small rope round a ruptured feedI think "W. G. C." will find from 6in. to 7in. throw suit-pipe, so as to keep the boilers in water till a new length able for him.-W. could be cast to replace it, the boilers working at about 25 lb. pressure ?-E. N.

[5219.]-POONAH PAINTING was, and perhaps is now, a fashionable accomplishment taught to young ladies, by which birds, butterflies, and flowers were produced "without any previous knowledge of drawing." Very much like stencilling as regards artistic effect and method of procedure.-PATERFAMILIAS.

[5244.]-MOUNTING BUTTERFLIES' TONGUES.Can any correspondent tell me how to mount moths' and butterflies' tongues to keep them open; under my hands when mounted they are so closed ?—V. P.

[5245.]-POWER FOR CIRCULAR SAW.—I should feel obliged to any of your correspondents that will inform me the power necessary to drive a circular saw for ripping out stuf up to 3in. in thickness.-FRANK CHESSELL.

[5256.]-BREWER'S TRUCK.-Could any of your mechanical contributors furnish me with a plan for constructing a truck with two wheels, more than 2ft. in diameter, and which would carry, without rocking, a barrel, a half barrel, or a quarter barrel?-P. J. M.

[5257.]-TUNING SPANISH GUITAR.-I have a Spanish guitar which will not tune to concert pitch without the top strings breaking; should feel glad if the "Harmonious Blacksmith" or some other musical render could help me out of the difficulty as to where the fault lies, whether in the strings or the instrument itself.-PUZZLED.

binding wire; could any one oblige by giving me a full [5528.]-WIRE DRAWING.-I want to draw fine iron description how to draw, say, No. 18 into No. 34; how to soften it, and what tools to use?-BINDA.

[5259.]-TELESCOPE FOR SPECTROSCOPE.-Will "F.R. A.S.," Mr. G. Davis, or any of your numerous correspondents inform me how to construct a telescope to adapt to a spectroscope; the number and nature of the lenses required? Or if they know of any ordinary achromatic telescope that will answer the purpose, and will give me the maker's name, I shall feel greatly ob liged.-SPECTRA.

[4260.]-PLANING SCALEBOARD.-Will any fellow subscriber tell me with what kind of machine to plane scale board, such as hat-boxes are made of, and at about what power to drive it ?-BROTHER CHIP.

[5201.]-INDIA-RUBBER.-Will some subscriber in. form me how to make vulcanized india-rubber adhere

firmly to glass?-W. H. W.

[5262.]-SIZE AND POWER OF BOILER.-What size of (locomotive tubular) boiler and thickness of plate shall I require to work two cylinders 3in. diameter and 6in. stroke; also how many tubes, and what size; what pressure would the boiler bear, and what is the working pressure of the same ?-G. V. R.

[5268.]-DANIELL'S BATTERY.-I am constructing a galvanic battery on Daniell's principles. I have made four copper cells measuring 5in. by 2in. diameter, also obtain a porous cell small enough to suit my coppers. four solid bars of zinc in. diameter. I am not able to of iron wires inside a thin cylinder of wood. On this I I am also making a coil. The core is formed of a bundle have wound 18ft. of copper wire with worsted; this 18ft. weighs Alb. On this I have wound 150ft. of wire insulated in the same way; this 150ft. weighs 14lb. Would some of your kind readers answer the following questions:-1. Are my copper cells too small to be effective? 2. Will cardboard serve as a porous cell? 3. Is the worsted carefully wound a proper insulator? 4. Are the wires in the coil of the proper sizes ?-JACOBUS. [5264.]-MASTIC GUM.-A subscriber is requested to inform the writer how to dissolve mastic gum in spirits of wine.-T. C. B.

[5265.]-DISSOLVING ISINGLASS.-How can I dissolve isinglass in spirits of wine?-T. C. B.

[5266.]-POLISHING MOTHER-OF-PEARL.-What are the means adopted for putting tine polish on motherof-pearl?-T. C. B.

The English Mechanic

AND

No doubt we can all see the evil of this. Is it possible to rectify it? It is to our mind a very painful thought that men should find, when too late, that they have mistaken their profession. There is so miserable a self-consciousness of

WORLD OF SCIENCE AND ART. having run counter to Providence, and therefore

FRIDAY, OCTOBER 28, 1870.

IDIOSYNCRASY.

THAT man is an inventive animal is beyond all tition of evils that we cannot fail to

HAT man is an inventive animal is beyond all necessity arise, than forth from the ranks spring a dozen willing volunteers, and the demand made upon inventive faculty is met and answered. But inasmuch as civilization constantly creates new and hitherto unfelt necessities, of which there has been no previous experience, it is evident that each generation must furnish minds equal to the emergencies of their own times, just as we find practically that a Stephenson and a Brunel arose precisely when the growing necessities of the civilized world demanded the cominencement of that system of railway communication, which by gigantic strides has reached its present magnitude and importance.

placed within their breasts solely and evidently the ingredients dispensed differently would have
to be their guide in life.
brought about more satisfactory results. If,
therefore, we allow that Providence knows what
is best for us collectively and individually, let us
no longer act as we now do in unjustifiable an-
tagonism to that all-seeing Guide. It may be
often difficult to place a son in the position for
which his tastes incline him, but it is not generally
more difficult than it is to place him in a pro-
fession antagonistic to such tastes, and the ulti-
mate result of doing what is wise will more than
repay the cost. Far better would it be to put a
son who is naturally mechanical into a fitter's shop,
than to make him a clergyman because there is a
good living in the family patronage or because an
uncle happens to be a bishop or a leading M.P.
The file may dirty his hands, but will leave his
heart cleaner by far than it will ever be if, with
no special love of the clerical profession, he
should enter holy orders for pecuniary advantage;
and, indeed, to put it no more serious light, he
is spoilt for a parson and lost as a mechanic, and
all through life he will give more attention to the
latter than to the former line of thought, cease-
lessly regretting his false position, and conscious
that he is keeping out a better and more able
man. With respect, however, to the clerical pro-
fession, no evil has been greater than this; be-
cause an outside ill-natured world takes its cue
from these very blunders of society, and is ever
but too glad to be able to pick such holes as these
in our clerical cloth. It is, however, the same in
all professions and trades, and no one can over-
estimate the mischief that is done by not follow-
ing out the evident design of Providence in giving
to individuals special tastes or idiosyncrasies
The whole balance of society is upset and dis-
arranged by our too-common shortsightedness
in this respect.

of having done in their generation far less for themselves and others than they ought to have done so ceaseless and hopeless a desire to rectify the one fatal mistake of life, that we cannot fail to sympathize even where we cannot aid. But why should we, after the discovery of such error, continue from year to year to repeat it? Why cannot we for the future guard against a repetition of evils that we cannot fail to deplore? The we lose our best men, and they in turn stand in the way of others, while doing little good themselves. We find, in consequence of the universality of the evil alluded to, a race of men called "Amateurs," and specially "Amateur Mechanics." A society, in fact, of these has been established lately, from which it is not unlikely great benefit will result, and which certainly would result were it not for the jealousy existing between these and the professionals. Who are these amateurs? Very generally men whose special abilities and natural powers are lost to the community. Men of great talent and often great manipulative skill, who, if they had not made a fatal mistake in the selection of a Now it can hardly fail to strike the thoughtful profession or trade, would have been most emiand intelligent that, inasmuch as men's minds are nent in many cases as mechanical engineers; and variously gifted, and each individual attached to who, even when of more limited powers, must some particular line of thought, constituting have done more general good if they had followed special tastes or idiosyncrasies," Providence as a profession the idiosyncrasies natural to has given to man, as a whole, an innate power them. We always feel that a first-class amateur of adapting himself to the various emergencies mechanic is a lost man. of his present state. The same Providence has also herein indelibly stamped man as a social being no simple individual being capable of supplying from the resources of his own mind the various wants that of necessity arise as the civilization of the world advances.

66

From this it would appear further that the highest perfection of human society would be that in which each should develop to the utmost, for the general good of all, those special faculties with which he feels himself gifted. If he fail to do this he must almost necessarily frustrate the designs of that Providence who adapts so perfectly every part to subserve the welfare of the whole. It is, nevertheless, a self-evident fact that this providential order and arrangement is more or less constantly marred by individual thoughtlessness, indiscretion, or selfish design. Men evidently intended for one special line of life persist in usurping that of their neighbours, and the perfectly designed machinery of human society is thus (to use a mechanical expression) thrown out of gear.

Why cannot "society" relax old worn-out laws and usages, and make better use of her resources? Why must we have this eternal treading on each other's toes in our walk through life? If a boy has evidently mechanical tastes, can society never be made to understand that for her own sake those tastes should be specially cultivated; that every known and apparent arrangement of Providence should be thankfully received and worked out. It certainly is a mistake, and one that is sure to cause evil of one kind or another to drive a boy into a profession counter to his tastes. It is a moral cruelty to do so; and in every case it is to the detriment of the very profession or trade selected that this rule of contraries is pursued. Yet, because the father is an officer, or a clergyman, or a lawyer, or engineer, the son is too often expected to follow in the parental footsteps. Hence our inefficient clergymen, soldiers, or artisans, who, respectively failing to become eminent in their own adopted professions, not seldom become amateurs in others congenial to their tastes. The great Never, perhaps, was this more palpably ex- Brunel was educated for holy orders, but was evenemplified than in the Working Men's Exhibition, tually sent to sea, thus losing much valuable time now open in Islington, in which we find intellect which would have been better spent if his natural of the highest order developed in the most varied tastes had been more exclusively cultivated; and and diversified manner possible, and comparatively it was only when driven by the French Revolution seldom in that direction which circumstances to take refuge in America that necessity led him to would have led us to expect. How comes it that give up all else for the pursuits which eventually the working shoemaker, left for a brief moment made him eminent. William Symington is another of relaxation to himself, dives into the mysteries instance of the same error in those who had the of astronomical and optical science, executing in charge of his education, and of the selection of a masterly manner work entirely foreign to his his line of business. He was educated, like trade, and producing a telescope of good design Brunel, for the Church, but luckily abandoned and practical use? "Ne sutor ultra crepidam this intention before ordination, and followed his is thus no longer a rule without exception. Then natural bent of mind. Instances may be indewe find a carpenter constructing a model loco-finitely multiplied of these false starts in life, motive engine; a gold-chain maker, a stationary sometimes happily rectified in time, but often horizontal engine; another carpenter designs and followed, through force of circumstances, until executes an harmonium; a jewel-case leather- too late to turn aside. The community of our worker, a glass fern case; a tailor, a set of world requires men of every profession and trade. designs for furniture; and very generally there is We must have engineers, mechanics, clergy, ample proof that a large majority have embarked scientific and literary men, to say nothing of in trades not naturally congenial to their tastes, so soldiers and sailors, merchants and tradesmen ; that when a spare moment dawns they are fairly and, on examination, we find Providence supplying driven back to that line of life for which they this need, and inclining different men to different were designed by Providence. Pass from the pursuits. Why, then, should we ti.us make such trades to the liberal professions, and we find able bad selection of raw material, and try to bend to lawyers in clerical instead of legal robes, and vice our special desires what Providence intendedversa; and among our clergy generally we become and that plainly and manifestly-for other purpainfully aware that men thus settle down to a poses? Necessity may compel us to make paper profession not only evidently uncongenial to their from straw and wood and grass, but we all know tastes, but which at every leisure moment is set how poor it is when made; and although we use aside for the pursuit of that department which shoddy for cloth, we do not venture to say that Nature designed them to occupy. And so it is in the quality is what we could wish. It is the same the world at large. Thousands are not in their with human beings. We may make a mechanic right groove," and therefore are not furthering into a parson, or a doctor into an officer, or make the welfare of society, as they might and would any other similar mistake; but what is the result have done if they had followed those natural generally? A life-long proof that we made a bad feelings which, be it remembered, Providence selection from our mass of raw material, and that

THE PROPERTIES AND POWERS OF THE
LENSES USUALLY USED IN COMPOUND
MICROSCOPES.

By THOMAS ARMSTRONG.

LENS is a piece of glass or any other are so formed that rays of light, by passing through it, are made to change their direction, either tending to meet in a point beyond the lens, or made to become parallel after converging or diverging. When a transparent medium other than air is included between two curved surfaces, or a curved surface and a plane one, it is called a lens. Lenses are of various species according to the character of the curved surfaces which bound them. But those which are almost exclusively used in optical instruments and optical experiments are bounded by spherical surfaces, and to these, therefore, I shall limit my observations. Spherical surfaces combined with each other and with plane surfaces produce the following six species of lenses, which are denominated converging or diverging, because the first class render a pencil of parallel rays incident upon them convergent, and the second class render such a pencil of rays divergent.

Converging lenses may be of the three following species:-The meniscus, the plano-convex, and the bi- or double convex. The form of the meniscus lens may be conceived to be produced as in section figure, No. 1, see diagram. It is

called periscopic, from the circumstance of objects | magnifying powers shall be expressed by reference being seen (when viewed obliquely through it) to visual magnitude seen at 10in.; thus, if we with more distinctness than through a double say that such and such a lens magnifies an object convex, or even a plano-convex lens. The form three or four times, it is meant that it exhibits it of the bi-convex lens is as shown in section with a magnitude three or four times as great as figure No. 2. It is bounded by two convex sur it would have if viewed with the naked eye at faces opposite to each other. The plano-convex 10in. lens, see section Fig. 3, is produced by a spherical and a plane surface.