[1238] IN reducing silver ores In the presence of oxide of lead, iron crucibles are generally employed; earthen crucibles lined with charcoal may, however, beesti nated by either the wet or dry assays. The dry When silver ores contain copper, the latter metal is used, but as it is a rather difficult task to properly ass y is used when the copper is in excess of lead, or line them, the ironjones are much to be preferred. An when that metal is not contained in the sample, and iron crucible, such as that described in the lead assay, th, wet assay when lead is present or when very great with fluxes, is very convenient. A section of this acuracy is required in the estimation of the copper. crucible is shown in Fig. 1. Its dimensions have already been given. When an earthen crucible is the trouble of adopting the prolix mode of wet copper En passant, I may remark that very few assayers go to employed the yield of lead from the litharge is, as a rule, much below the proper quantity, owing to a silicate assa, described by "Augustus" in his letter to the of lead being formed, and it is therefore necessary in MECHANIC, a few weeks since. I have assayed copper ore both by the wet and dry methods of assay, and I the cupellation to add a certain quantity of poor lead, i.e., lead free from silver, to the button of rich alloy yielded plume myself that I have done so successfully, yet by the crucible in order to prevent too great a loss filters, ad hoc genus omne, and yet I affirm that I have in wet assaying I never used H2S, never burned my from absorption. Of course when the crucible is not been astray one half per cent. five times in one properly lined there is no danger of a silicate being hundred assays. Query, does not the amount of formed as the charge is prevented from coming in contact with the silica of the crucible. filtering, &c., described by "Augustus," occasion as directions would entail? I shall return to this subject much loss at least as the neglect of some of his I inform him that I never measured my ammonia, and on a future occasion; but what will " Urban" say when yet have not, up to the present, made an error involving

brevity as much as possible, and therefore the letters his apparatus will serve your readers to understand my of reference used by "C. D. C.," page 352, to describe modification. I have only used four extra reference letters, W X Y Z, by this means saving nearly a column of your valuable space.

Fig. 1 shows the apparatas complete; Fig. 2, the case, with its inlet and outlet pipes; and Fig. 3, the float, with its attachments.

K K, has a stuffing box, Y, through which the rod X In Fig. 2 it will be noticed that the top of the dome, slides airtight. This rod is fixed to the top of G. At the top of the rod is fixed a tin tray, Z, for containing shot to load the float. Fig. 3 shows the float, which is conical. Above and below it is a wooden disc H, which rests on a brass ring W, soldered over the tube G. The advantage thus obtained is that by loading the float (by simply putting more shot in the tray) it can be sunk an; distance, carrying the wick with it, and immersing it whatever is necessary, and thus by altering the

dicular; and in such a direction that the platinized
ganze shall be, as it were, uppermost. The reason of
this is obvious; for, as the gas finds its way to the sur-
face in perpendicular lines, such a disposition of the
arrangement will at once admit it to pass through the
interstices of the gauze, and readily to escape by the
A still
desired channel-the outside of the gauze.
more powerful apparatus may be constructed by em-
ploying a ganze on each side of the zinc. In this case
the zinc must be perpendicular, and the gauze not
exactly parallel, but rather closer at the top than
below."

I have taken a great deal of interest in galvanic batteries for many years (not for the last two years only, as Wm. Toakes kindly or unkindly suggests in his letter, 1136). I would ask Mr. Sprague: 1st. How is it Messrs. Elkington & Co. employ the common copper acid battery in their electro-plating establishment in preference to any of the improved forms? How is it Messrs. Gore, Watt, Napier, and others recommend the same in their works on electro-metalinrgy? 2nd. As to iron, it has been recommended as an improvement on the copper acid battery by the late Wm. Sturgeon, and by Mr. Martyn Roberts, and I would ask him how it is he so briefly condemns the Sturgeon battery, when its author, according to his experiments, obtained from it such excellent results, which were approved of by some of the leading electricians thirty years ago?

There is one form of single fluid battery I should have been pleased to see amongst those treated upon by Mr. Sprague (although I must confess he has made an excellent selection, and he could not be expected to speak of every variety of form), as I believe it is excellent for electro-plating purposes-I allude to the "Triple Contact Pile," invented by Professor Francesco Selim, of Turin, about fourteen years ago.

both by electricians and writers upon electricity I
adopted it, in order to avoid the constant repetition of
"central core," core of the coil, bundle
the phrases
of wires, &c., when writing upon the induction coil. Of
all others, I think a member of the faculty should be
the last one to throw stones at bad Latin in a technical
term, considering the extreme tennity of the glass case
in which the technology of the profession, technically
called "dog-latin," is enshrined."

It was my intention to say a few kindly words to
"M.R.C.S.," but finding him already in the practical
D. H. G.," I leave him there;
hands of" Unit" and
but cannot with equal reticence withhold my Damoclean
sword from the conscience of another gentleman, who
without permission, and probably with the caution
"Please not to touch the models" staring him in the
face in large capitals, yet coolly takes another man's
model to pieces, and finding he cannot make anything
of it, quietly rushes to "OUR JOURNAL" to solicit a
description of it!

I assure you that I have the "kakoethes scribendi
upon me just now, but I am in too good humour at
this moment, so I put a dot to the sentence and pro-
ceed to better subjects.

(6134.) Electrical. Who will help me? "Colonel
B." cries, despairingly. I will try.

"Morse key" in-
All that you require is a simple
stead of the one you now use; any mathematical
instrument maker will show you one. It consists of a
brass lever suspended on an axis, at equal distances
from which axis are placed two studs tipped with
platinum. On the base-board to which the pillar that
carries this axis is attached are fixed two plates or
studs, also tipped with platinum, one immediately un-
der each of the studs of the lever

The two bottom studs and the centre pillar are in sulated from each other; a small steel or other spring As to letter 1136, I would ask are such remarks worthy is placed under the long end of the lever in any conof any correspondent desirous of helping his fellow- venient position so as to ensure good contact between reader? What has pluck (unless it is our worthy one of the top and one bottom stud, while on depressing editor, who certainly deserves to be called plucky, if not the key you break that contact and make a new one something more noble)-what has pluck and vanity to with the other pair of studs, and on releasing the do with the ENGLISH MECHANIC, or an occasional lever it at once assumes its former position. And What little I know I will now for the disposition of your circuits. You have correspondent like myself? willingly communicate to my brother-readers when I four wire ends from your two magnets. Connect up see it asked for. Wm. Tonkes has been silent a long one end from each magnet, say to the + pole of your battime, and yet our journal has not "collapsed." I do tery, and couple up the other two ends, one to each of pole of your battery, taking not forget his language to "Sigma," and others in the the studs on the base-board; then join the pillar which I sent carries the key lever to the bichromate of potash battery controversy. particulars of the copper carbon battery, invented by care that the type wheel magnet wire is connected to The wheel no less a person than Professor Jalius Thomasen, of the stud in the base-board, which is always in contact Copenhagen, which he spoke of in a-well, I will not when the lever is in its normal state. Turning over the pages of the ENGLISH attached to your handle in the lower part of your diaMECHANIC for July 24th, 1868, in reply to" Gas Carbon," gram, and the means you use for making and breakI find the following information given by this modern ing contact there, will remain just as they are, care Eurylochus, "but your correspondent must remember being taken that they are in connection with the type that it is the cathode and not the anode which is dis-wheel magnet only. Carefully trace out these instrucsolved in electrolysis." Then follow some very in- tions in a diagram, and trace the current before and tobacco-pipe after depressing the key, and it will do you more good teresting information about common heads. I do not like personalities, but those who live than if I had sent a diagram myself, as it will make in glass houses, &c. I shall not allow myself to be the arrangement clear to you step by step. If anything appears clondy write again, and no doubt our Editor betrayed into anything like this sort of thing again. will print a diagram with any further particulars I JAMES HOWARD. inay find necessary to give.

say.

A CHEAP MICRO-POLARISCOPE. [1242) ALLOW me to suggest one or two slight improvements in above, as described by me (let. 1125, p. 373). If any correspondent making one has thin for microscopic covers he will find twelve of them analyzer and twelve for polarizer better than the thin window glass, because they will occupy less room and absorb less light, and if appearance is of consequence, the brass tubes of a common sixpenny toy telescope One tube, with cut short will make a very good cell. the ring from the next one for it to turn in will make a capital polarizer with the thin glasses fitted in as described, and if a small casting of white metal be made to affix it to the microscope, and the ring cast fast in one end, a very good-looking and firm arrangement will be secured. The casting may be of the shape of figure, where a is the end for the polarizer and the black interior line represents the brass ring imbedded in the white metal, b the hole for stem of microscope. I would only add further on this subject that almost any colour may be got from a single piece of mica by tilting it at various angles just under the stage of the microscope. The slightest variation of position produces remarkable changes.

I should like to counsel any reader who has yet to purchase a microscope not to be led away by the idea that objectives of a large number of degrees aperture

are

better to work with than those of smaller. They only waste their money who buy them, excepting for very special purposes. A very little consideration will convince any one that the definition of wide apertured objectives cannot be true. We see a distorted representation of a natural object, unless every part of it lies in the flattest of planes. It is like taking pictures of an object at one side of the room from every point on the other and jumbling them in a confused mass. It utterly destroys any true perspective effect, for an extreme aperture looks round at the back as well as EDWIN HOLMES. front of the objects.

ELECTRICAL-BOILER EXPLOSIONS. [1243] I fEEL obliged to Mr. Proctor (let. 1117) for pointing out to me a correlative instance of solecism in the coinage of technical terms, especially for one coming from so excellent a coiner. I do not make a practice of studying the etymology of every term I write (who does ?), and finding the word fasciculum used

(6142.) A thorough and I hope decisive definition of
each of the three terms mentioned has already been
begun, and will no doubt shortly be concluded, in Mr.
Sprague's articles on Electricity, and I hope no less able
pen will enter upon the subject until his definitions
are given.
(6152.) The Ruhmkorf Induction Coil is not adapted
Secondly, no large coil yet made
nor intended for the exhibition of the electric light
properly so called.
and used with many cells will produce it, much less
then a small coil with three or four cells. Thirdly, the
secondary coil can be increased in length within given
limits with good effects, joints being well made and in-
sulation properly attended to, the latter more par-
ticularly. Fourthly, the power can be reduced by
altering the tension of the spring of the contact-
breaker, by reducing the number of the cells, by
lessening the surface of contact, or increasing the dis-
tance apart of the elements in the cells, by introducing
greater external resistance in any part of the external
circuit, by bad contacts, insufficient insulation in every
part, by-but, in a word, by mal-construction;
reverse these various modes and increase is the result.
Fifthly, in all induction coils intended for showy
effects a condenser is indispensable, as is also a con-
tact-breaker (which is really a commutator), but the
commutator proper is a matter of convenience, and is
never absent from a good coil.

(6136.) Boiler Explosions." Tobias" asks for the
"favour of a few words" on this subject. I have
written many, even recently, but for every one of mine
ten thousand have been written, and still our daily
papers tell us horrid tales of boiler explosions. The
spheroidal condition of water may take place within a
boiler, in fact, Mr. Perkins is said to have proved the
case; but I do not remember reading that the boiler
which contained the water in a spheroidal state, was in
cast. In fact, "the water would not come out," hence
the habit of bursting and spreading destruction broad-
cae inference is that the boiler did not burst at all:
Why was this when, from the known principle founded
upon experiments, iron decreases rapidly in tenacity,
after a given temperature? But as the boiler did not
burst, we arrive at the conclusion that it was made
strong enough to resist all the internal forces brought
to bear upon it. And this gives rise to the interesting
"Are the boilers which do burst built upon
question,
the same safe principle, and, if so, are they maintained
in that condition?" Again, I am not aware that Mr.
Perkins's boiler burst either when the water was attain
ing or when losing this spheroidal state, consequently
it must have passed through all the phases of trial,

and some very, very rauch beyond that to which any
ordinary one is or can be subjected, unless we intro-
duce that fatal element so glaringly apparent from the
reports of the associations I named, yet so little
appreciated, less perhaps understood, nay, quietly
until the dread reality is forced upon them, by finding
shelved, in spite of all experience, by boiler owners,
victims are ushered into eternity, the unfortunate
that "another boiler explosion" has taken place, the
water, which had amassed a fortune and has now
wrecked it for the owner, is brought before a coroner
and twelve good men and true, and accused of going
into a "spheroidal state," and thus causing all the
mischief. That which cannot speak they say cannot
lie, either, unfortunately, can it tell the truth, in this
case especially; and water is condemned for having
dared to enter into the "spheroidal state," while the
owner goes forth into the world a respectable, much
sympathized with, out often a ruined man.
my intention to set up any new theory, and certainly
not to discuss the merits of old ones, because I am
firmly convinced that a careful perusal of the reports
boiler owners more clearly to the course they should
of both the associations I have referred to will lead
pursue than all the theories put together. It is their
business and to their interest to do this, nor is it any
the less a duty to those they employ that it should be
done, and that too with a will.

It is not

Being unable to write last week, I had almost forgotten to note letter 1106; I am sorry to find He prefers both wheels rethat S. F. Hunwicke has, in his last paragraph, thrown away the only chance left open to him of the first law of motion, a pair so detached from the justifying his sketch. maining attached to their axle; be it so, but then, by carriage would run in a straight line, forming a tangent to the curve on which the vehicle had been running, and not the curve line shown on sketch. On a to the right or left; in fact, their very shape is a great perfectly straight and level road the conical form of tires gives no tendency to the carriage to swerve either safeguard against such lateral motion, but when we of motion. Two such expedients have been adopted, have curves to deal with, we must have expedients to meet them, in order to fulfil mechanically this first law viz., raising the outer rail so as to change the posi The other is coning the tires, tion of the centre of gravity of the whole vehicle, of every curve. and this can be done to meet the particular case which really means using a wheel of larger diameter diameter to describe the same arc of a smaller one. to describe the arc of a larger circle, and one of smaller Theoretically these two expedients properly comcurve with the same degree of freedom, so far as the bined will enable a vehicle to run round any given grinding of flanges of tires and friction due to slipping of the outer wheel are concerned, as if it were running on a straight line of rails; practically, we know that flanges do wear thin, and flat places will occur in the tread of the tires, but we must not condemn on this account a principle proved to be true, but those who mis-apply it by not attending to the details necessary for its correct utilization in practice. On some of our lines of railway great difficulty exists in adjusting these two expedients on account of the great number and varying radii of the curves, but if the cone of the wheels to meet the worst case is employed the amount of conicalness is determined upon most if it will most assuredly meet the conditions in all other cases, and this I believe is the principle upon which not all railways. I hope I have said enough to confor if they do not meet the exigency, cylindrical ones vince Mr. H. that coned tires are alone admissible, cannot, unless they are loose on the axle; and in my first note on this subject I pointed out what has so far I will conclude for the present, by a note of admirabeen held an insuperable objection to such a device. "W. A." tion of the manner in which "W. A." (letter 1077), 'Sigma" through Pulvermacher's chains. "has worn these chains and found them to possess a clenches the nail driven home by the ability of upon these wonderful stimulant to flickering vitality :" will" W. A." kindly inform me, "who the medical or other men are who have passed ridiculous eulogies chains, or any of a different character than that which he voluntarily assigns to them, and where these eulogies have appeared? The basis upon which he "But they (the chains) appears in his next sentence. appears to assume that such eulogies are ridiculous are spoken of as if they were a discovery, rather than electricity." a convenient application of generating and applying

Now it has been affirmed that the two greatest events of the fifteenth century were the discovery of printing and the invention of America. If I am to take the meaning of the word" discovery "in " W.A.'s" macher will agree with "W. A.," and so will all of his letter in this light, I am confident that Mr. Pulvereulogists, for he never laid claim to the "discovery of the chain band, but simply invented and patented it. Moreover, the claim he makes is not that he has done before him did do, and in justice to him I must add that which no one else could do, but that which no one that no one up to the present time has done in the same masterly manner. Why, we may as well take Watt down from his pedestal because we have discovered that Hero made a steam-engine about 130 B.C., or declare that Hoe's printing machine deserves no eulogy because Caxton printed in the fifteenth century, or a hundred other absurdities might be adduced, but not one derogating an iota from the just claims of J. L. Pulvermacher, as the original inventor of the chain band. Certes he has not aimed so much at cheapness as excellence, and has attained his object in that direction. When any one else can compete with him without infringing his rights, probably he will lower

his prices as all other mercantile men do when they
find the market glutted; in the mean time he must pay
himself at the expense of those who can afford the
luxury of his chains, for the time, brains, and money
expended in producing and perfecting his invention.
How far "W. A." was qualified to pass sentence of
"ridicule" upon those who have eulogized Pulver-
macher's chains may be seen in the fact that although
he had used them and found the benefit he deseribes
from them, yet he has slavishly followed the instruc-
tions given by "Sigma," good as they undoubtedly are,
without an atom of originality in himself, and winds
up by asking" which element determines the positive
pole in his arrangement"! Now "Sigma's "instruc-
tions were only given last month, while in 1848
Mr. Pulvermacher obtained damages to the extent of
£10,000 for breach of trust and unlawful use of his
patent right, as being the original inventor of galvanic
chain bands. Is further comment necessary?
WM. TONKES.

CURVATURE OF THE RAINBOW. [1244] THERE is an old story of a stargazer who was so absorbed in the contemplation of the heavens -perhaps wondering at the false stereoscopic views taken of the moon-that he fell into a ditch. I do not wish to be rude to "E. L. G." (let. 1144), but I venture to advise him to look a little more into matters meteorological before putting his foot into them, and to prefer a sure but roundabout road to a short cut leading into the mire. As "E. L. G." confesses that he has never read any work on meteorology, I think he is scarcely justified in attempting to answer questions on the subject. The offhand manner in which questions are sometimes answered in the ENGLISH MECHANIC, and the bold way in which "mistake" is imputed to conscientious students, deserves, in my humble opinion, the severest condemnation. It leads those numerous readers who have not text-books at hand to doubt the truth of every answer, whether replied to or not, and I am sure all will agree with me in seeing the necessity of placing some restraint upon too willing but incompetent teachers.

As far as regards Mr. Preston's remarks about atom theories I take the liberty of informing him that what I advanced has but one novelty, and even that was a mere simplifying of the theory put forward recently by an American savant, as set forth in the Philosophical Magazine. I cannot agree with him as to the inutility of even absurd theories, as they provoke such entertaining and instructive replies from the more gifted correspondents. We cannot all be princes of science, but why should not all contribute something?

M. PARIS.

OF MR. PROCTOR'S ALGEBRAIC FORMULA.

the fullpoint's use as denoting, as it is so often
[1246] MR. TONKES may be right in objecting to
used as a decimal point; but I would further advance
as a rule that no formula be used which could possibly
be misread as to the limit on either side, to which any
of its symbols are intended to apply, however they be
page 361,
No. I. of the "Differential Calculus Lessons," may I ask,
as a mere tyro in algebra, does the formulate
mean, as I take it to do, ? This form would be

understood in "first-class" seminaries. At

0 x 12
2

less liable to printer's misreading than the one adopted, and as it is most important that Mr. Proctor adopt a style in which he can be followed by many of your readers I think it very desirable that he give the real quantity, as well as the algebraic letters used in calculation, in the way of definition to all his known quantities. If the simple formula used by Mr. Proctor could be proved by Arabic figures it would give confidence at once to the student, who could then have full faith in the process. To me, more stupid I trust than your readers generally, it is hard to conceive of a space represented by gravity multiplied by time squared, the result divided by two; and I should like to put it to a show of hands whether or not he is aiming too high for utility. Mr. Proctor certainly defines g as 32-2ft., but from first to last t seems to remain undefined and unconverted into any known quantity, With respect to the radius of curvature of a rainbow, and to know at last that the "value" arrived at is if the question be answerable at all, "E. L. G." hast, even, is to know no value whatever, never having fallen into a not unusual error of confounding a visual learned what real number of seconds t stood for. angle with a radius or semi-diameter. He will see Now, say g= 4 ; t 2: this at once, when I ask him whether a curve on a 4 x 4 railway having a radius of 42° 20' is too sharp for Then t 2 safety, or if he will construct for the benefit of his fellow-readers a circle having a radius of that measure. The red ray mentioned in my letter is that found in his own letter (p. 259), and I suppose the extreme ray of the text-books. There are not "red rays at every part of the space wherein the bow appears,' "unless "E. L. G." seems to think the rainbow is a conewhich supposition is simply preposterous. I cannot help what almanacs state about the sun; I believe at

=

Theng (t + 1)2

=

end of the 2nd second.

Then 18-8 2nd second.

=

4 x 9

2

= 18 as space traversed at

= 10 as space traversed during the As it is desirable to extend the instruction to be had from Mr. Proctor's lessons as widely as may be, I trust my humble hints will be taken, as they are in

unit of comparison the amount of heat which passes through a perfectly exhausted cylinder; the source of heat being a cube of hot water.

I will conclude with a passage from the best French work on physics-Jamin, "Cours de Physique":Taking any determinate direction in the mixed spectrum, it is found experimentally to contain both a luminous ray and a concomitant calorific ray; they cannot ever be separated one from the other, and every action which diminishes the one diminishes the other equally. The theory of heat consists in supposing that the vibrations of ether which are less rapid and less refrangible produce heat without affecting the eye, and form the dark heat spectrum; that at a certain limit of and that then more and more rapid vibrations produce rapidity of oscillation they begin to affect the retina without ceasing to heat the bodies which receive them, all the colours from red to violet and all the corresponding kinds of heat. According to this hypothesis there would therefore be, in one and the same direction of refraction, but one single vibratory movement; but it the property and the effect of light and the property would have two properties and would produce two effects: and effect of heat. Consequently, it is perfectly clear that one will never be able to separate the two effects from one another, and that every action which weakens the vibration will weaken at the same time and to an equal extent the heat and the light which it produces." It remains for Mr. Liggatt to disprove this statement, and to show how the luminous solar rays can be con centrated on ice without at the same time producing J. G. GRENFELL. any thermal effect.

MOLECULAR FORCES, ETC.

this moment astrological almanacs are to be found in tended to promote accuracy with wide intelligibility in saying that the solution is not absolutely opaque to

mathematical formula.

FIVE INCH LATHE.

J. BARWICK.

[1249] I SHOULD be glad to know whether "S. P." (let. 872) is sure of his fact that if a luminous ray ei determinate refrangibility be passed into a solution of iodine in bisulphide of carbon, a heat ray will pass through the solution. The only account of such an experiment which I have seen is where the total radiation of an electric lamp is passed through the solution. which is then stated to stop the luminous rays and to transmit the obscure heat rays. The prism was not used in the experiment at all, and, subject of course to experimental correction, I am strongly of opinion that no heat would be transmitted if the solution were placed in the path of the luminous rays only. Mr. 8 as space of 1st second. Preston (let. 1128) says that heat would no doubt be transmitted; but he does not state it as a fact, and his arguments do not appear to me conclusive. He says that the question is one simply of reduction in intensity. Now intensity depends on amplitude of vibration, and has nothing to do with wave length, and if the ray merely diminished in intensity it will after passing through the solution affect the retina as a light rayat all events it would do so if a sufficient number were collected by a lens. But this is simply tantamount ta light, and so far is contrary to experience. If, how ever, Mr. Preston means by change of intensity a change of wave length, he makes a statement for which I know no authority. If this were possible, why shonl we not find a solution which would take, say, a blue ay, make a slight change in its wave length, and transmit it as a yellow ray? A colourless solution of alum is stated by Tyndall to be absolutely opaque to obscure heat-there is no mention of diminished in exist; the motion is taken up by the molecules of the solution. The case is the same with regard to the luminous rays and the iodine solution. The waves break on the solution, and cease to exist as surely as an Atlantic billow on the Irish coast. If the solution be exposed to the light ray for a sufficient lengta of time its molecules will, of course, begin to vibrate under the constant impact of the tiny waves; but their motion will be slow, and the waves they will give rise to will be of far greater wave length than those of t luminous ray-that is, the solution will give out obscure heat rays without a trace of light of however faint intensity. Mr. Paris (let. 1027) seems to me to give a very good explanation of how obscure heat rays might get mixed with the light rays, but I should be glad to know whether the experiment has been tried with the iodine solution and the special apparatus for obtaining a pure spectrum. I cannot see why Mr. white light." Superimposed is perhaps the best ward; Preston objects to the term "intermixture of rays in but Tyndall speaks of the prism as "disentangling" the various rays, and the other metaphor is perfectly intelligible, and in common use.

all Government offices. The rainbow is no more a mere appearance than the sun's surface. In both cases light and matter are engaged. If "E. L. G." can see a bow in a fountain, and at the same time a rainbow through it, he must have invented the Wellerian optical apparatus described in the case of Bardell v. Pickwick. The diameter, semi-diameter, or radius of a rainbow is as much a measurable quantity in miles or yards or feet as the surface of the sun, so much so that by observing carefully where piece between and below the letters D D is shaded tensity, but of simple opacity; the waves cease to

the arc touches the ground we can calculate the distance of the drops. I would, therefore, in the interest of all readers of the ENGLISH MECHANIC treat the answer of "E. L. G." (p. 259) as a bad case of replying to a question upon a subject to which the answerer has confessedly paid no attention; and I think "E. L. G." deeply read, as he evidently is, on many subjects, has made the following mistakes:1. In supposing the rainbow to be a cone. 2. In stating the drops are, and must be, perfectly spherical. 3. That bows cannot be seen in mist. 4. That clouds are composed of water-bubbles or vesicles. 5. That a rainbow can be seen through a spray-bow. 6. That the rainbow is a mere optical appearance. 7. That its radius of curvature can be properly stated to be 42 20', or any number of degrees.

M. PARIS.

SOLAR SPECTRUM.-MOLECULAR FORCES. (Letters 1128, 872, 1027.)

[1247] IN the drawing (let. 1166, p. 397) of 5in. lathe heads the scale was omitted, so I may as well say that as it appears in print it is 5-32in. to lin. There is a trifling inaccuracy in Fig. 2, where the with vertical lines, they should be horizontal, as that portion is the back end of the bridge piece and is continuous with the back end of mandrel head, or in the same plane. I may here remark that both heads are a little one-sided, owing to the greater width of the front web of bed under which the screw lies, affording more room than there is on the other side. Without this being mentioned any one examining the drawings might think they were carelessly done.

LIGHT AND HEAT.

J. K. P.

[1248] MR. LIGGATT (let. 1129) again revives the unhappy ghost of Caloric which one might have hoped that Rumford, Davy, Tyndall, and others had finally laid at rest. He says that the sun's rays have no to melt ice in vacuo when concentrated by a power burning glass. I should be glad to know on what authority this statement is made. There is no record [1245] I think Mr. Preston has not clearly under- of any such experiment in any book on the subject I stood" S. P.'s" difficulty. "S. P." wanted to know have ever seen. If the experiment is Mr. Liggatt's how it was that rays having the same degree of re- own, minute details would be of the greatest interest, frangibility in the spectrum should some produce heat and in fact necessary before one could accept so reand others light. I answered that in the ordinary markable a statement. Has Mr. Liggatt tried the exspectrum there was throughout a mixture of rays of periment with a delicate thermometer instead of ice? all degrees of refrangibility, the reason being that the Supposing the fact to be true, we are at once met by the rays of the sun passed through the prism suffering re- difficulty that we must then believe solar heat to be quite fraction in different directions, owing to their original different from terrestrial heat, for it has over and over want of parallelism, and I further remarked that in again been proved that terrestrial heat can traverse a order to get a pure spectrum a special apparatus was vacuum. To show those of your readers who, like Mr. necessary. I now beg to quote for Mr. Preston's in- Liggatt, still believe in caloric and its inability to traformation a passage to the above effect in Weale's verse a vacuum, the difficulties they have to explain, it Series from the pen of Mr. Charles Tomlinson, but any may be worth while quoting a passage from Tyndall on treatise on light will explain this as well to him. In "Heat," p. 244:-"If it (a hot copper ball) were placed speaking of Fraunhofer's lines he observes-"The in vacuo it would still cool. Rumford contrived to hang a beam contains rays from all parts of the sun's disc of small thermometer by a single fibre of silk in the middle which those from the top are inclined 32' more than of a glass globe exhausted by means of mercury, and he those from the bottom, rays having the very same re- found that the calorific rays passed to and fro across frangibility, from their original want of parallelism, the vacuum; thus proving that the transmission of the being refracted to different parts of the spectrum," so heat was independent of the air. Davy with an apthat" every point of it receives rays of various refran-paratus which I have here before me, showed that the gibilities." Therefore it is that the part of the spectrum which contains light rays also contains heat rays, and in order to obtain the dark lines we are obliged by means of a narrow slit to reduce as far as possible the extent of the surface of the sun.

[1250] I BEG to add to my former letter (1151) on this subject a few instructions for the information of such persons as may not be practically acquainted with the manufacture of gunpowder, in order to enab them to make small quantities, free from danger, with the common appliances always at hand.

Grind separately the chlorate and prussiate in s a warm Wedgewood mortar, sifting out from time to time the coarser particles with a fine sieve, until the whole be reduced to an impalpable powder.

Then get a large twopenny churchwarden clay pipe, and fill the bowl with the lamp-black well rammed and luted down. Make the same red-hot in the fire, and when cold turn out, and grind and sift the pure carbon. Now mix all three in due proportion. as stated in my former letter, and pass them together through a sieve. The composition must now be quickly moistened with pure water, and made into a stiff paste

or dough by beating and rolling. Have ready a painter's
glass or stone slab provided with a fin. ledge on each
side, and with a glass rolling-pin, roll it into a sheet
of that thickness. This sheet must now be scored with
the point of a penknife into strips of the same breadth
or fin. Special attention must be had that all these
latter operations are entirely completed before the paste
becomes quite dry; if delay be unavoidable keep it
covered with a wet cloth. When thoroughly dry in the
sun or a warm room, the material may be gathered
up and separated by means of sieves, one being very
fine to take out the dust which will be found to be
excellent ammunition for small arms. If any grains
remain too large they may be gently rolled down with a
common glass rolling-pin or round ruler, and again
passed through the separating sieves.
This gunpowder will be found equal to the best 3s.,
and will cost about one-half if the materials be bought
from wholesale houses or dry salters.
HENRY W. REVELEY.

to "sin." as the number of times the operation of
deriving a sine from its arc is repeated, in which case,
(as in the Calculus of Functions) sin. a will be equiva-
lent to sin. sin. a; or we may take it as the numbe rof
times the ratio of sin.-1 a: a is repeated, in whichcase
it must stand for the third proportional, now written
sin. a

a

REPLIES TO QUERIES.

In their answers, Correspondents are respectfully requested to mention in each instance the title and number of the query asked.

[5109.]-ARTILLERY (U.Q.).-In looking over this week's number, I see amongst the Unnoticed Queries an inquiry as to the cost of the projectiles fired from With regard to Mr. Proctor's late question, how to represent factorials, I would suggest as preferable to heavy guns. The largest gun I know is Krupp's 1,000illustration of this weapon is given at page 104 of the The cost his in, or 160, the concise n!, or 60 !, and 602, and 602!, pounder (breech-loader), recently completed, the weight which I have seen both in English and foreign works. of which is 50 tons, exclusive of the carriage. A capital There is really something to exclaim at in the magni-present volume of the ENGLISH MECHANIC. tude and quick increase of this function for numbers of a solid projectile for this gun is about £15, and that beyond the lowest. In questions of chances it is quite of a shelf about £22; charge of powder, £5. The an admirable instrument, and I rather admire the life heaviest gun we have in this country is the 35-ton Woolwhere about £15; with a charge of 120lb. of powder, introduced into formula by this appropriate type, wich gun (muzzle-loader), throwing a shot of 700lb. which is one rarely in danger of running short, I think, weight. The solid shot cost about £10, and shell someE. L. G. costing £4. The heavy guns in position for the in a mathematical printer's point. defence of Paris are nearly all breech-loaders, throwing shot up to about 2001b. weight, as near as I can remember. may add that for artillery purposes the breechloading system is now thoroughly condemned in this as the 9-pounders used by the horse artillery.-ARTILLERY CAPTAIN.

ANTHROPODONTOIDES BAILESII (n. g.). [1251] I BEG your permission to introduce to your readers a description of a tooth of what I have good EXTRACTS FROM CORRESPONDENCE. country, and is only allowed for very light guns, such

reason for believing belongs to a new genus of carboniferous limestone fishes. The specimen upon which the genus so founded was obtained from the lower carboniferous coal-shales of Scremerston, near Berwickupon-Tweed; and the gentleman owing to whose kindness I received the fossil is Mr. Bailes, who is a colliery manager, and who for many years has devoted much attention to carboniferous fossil fauna.

The matrix in which the tooth lies imbedded is a hard shaley limestone, which originally rested upon the coal worked in the carboniferous limestone strata of Scremerston.

IMPROVED LIGHT FOR THE MAGIC-LANTERN.

The following is sent by an anonymous correspondent: -"Having experienced considerable difficulty in obtaining sufficient light from the ordinary solar oil flat) petrolene burner, and find it gives a most lamp, I have lately adopted a double wicked (lin. efficient light, the photographic pictures being developed very satisfactorily. It has also the advantage of being more cleanly, and less trouble to light and adjust. Any tinner will readily furnish one, care being taken in a small lantern that the burner is kept low, MEER The coal strata of Scremerston are the counterpart otherwise the flame may be too high for the lens." ΤΟ CUT THE THREAD IN AMBER of those which are worked at Gilmerton, near Edinburgh; and it is interesting to know that many of the SCHAUM PIPES, OR HANDLE OF UMBRELLAS, fossils found at Gilmerton correspond with those found WITHOUT LATHE.-Mr. S. Perry sends the following: at Scremerston, and differ from those found in the "Tap a piece of steel the size of screw required; file it true or upper coal-measures of Northumberland, in the down to 1-16 on both sides; chamfer off the two opposite neighbourhood of Newcastle-on-Tyne. Rhizodus Hib-sides the same as a common screw tool for lathe; drill bertii and R. lanceiformis are found in tolerable abund- the hole something less than the tool, which put in ance in both the limestone localities, but neither bradawl handle with slight pressure; apply a slow out any danger of breaking." species of this genus has been found in the South rotatory motion, which will cut a fine even thread withNorthumberland coal shales.

It was supposed by the authors of Pteroplax that R. lanceiformis corresponded in form with the teeth of Pteroplax cornuta, a reptile founded upon jaws and teeth discovered in the low main coal-shale of Northumberland; but such is certainly not the case, as the teeth of R. lanceiformis are long, slender, and slightly lanceolate, while those of Pteroplas cornuta are broad, flat, and very lanceolate, and bear a very small resemblance to those of R. lanceiformis. It may be safely athrmed that R. Hibbertii and R. lanceiformis have not been found in our upper coal-measures, and that the only horizon on which they have been found is that of R. lanceiformis need the carboniferous limestone. not, therefore, be expunged from the list of carboniferous fishes, as some local writers hastily suggested.

The tooth, sketches of which I annex, and for which sketches I am indebted to Mr. Thomas Small, is 5-16ths of an inch long, and 2-16ths of an inch thick. In its front aspect (Fig. 1) it resembles the symphisial extremities of the lower jaw of an infant, the small ridges presenting an appearance much like the small teeth which protrade from a child's lower jaw. The tooth, in its front aspect, is convex; in its inner aspect (Fig. 2) it is concave, and the appearance is like that of the inside of an infantile jaw.

FIGI

FIG. 2
TWICE THE
NATURAL SIZE

The lower part of the sketches represent the matrix in which the body of the tooth is buried, the denticular portion alone being visible. The denticles or ridges are six in number; they are not detached, but are structurally united, as is the case with Cladodus, Dipterus, Ctenodus, Ceratodus, Ctenoptychius, Hybodus, Poecilodus, Amphicentrum, Acanthodopsis, and a few The tooth is of a brown other Paleozoic fishes. colour, and is covered with a uniform coating of moderately smooth and somewhat iridescent enamel. T. P. BARKAS, F.G.S.

THE RATIO OF

or as I prefer

TELL-TALE OMNIBUS STEP.-The identical omnibus step advocated by M. Paris (let. 1034, p. 324), was brought into use in Paris many years ago, according to

"F.R.C.S."

DARK LINES AND NEWTON'S RINGS.-Should
"B. A." (let. 562, p. 87), require an easy proof that
the lines are due to diffraction I think the following may
be accepted. Let him approximate the tips of two fingers
and he will observe an appearance as if a dark liquid
were between them; at the same time he will feel they
Where the fingers touch the
He
touch each other, although by their outline seeming to
be some distance apart.
light is stopped and does not turn the corners.
should look at aflamp beyond. The experiment, I be-
lieve new, is worth trying.-M. PARIS.

SMELL OF METALS.-Willing as I am to adopt the
second hypothesis of "Sigma" (let. 1158), yet I cannot
think there is not an emission of particles. We know
andwe can prove that other odours are caused by the con-
tact of material particles with the membrane of the
nose, and as smelling is only the sense of tasting re-
fined, probably they produce some chemical change in
the secretions. Analysis of the bodies of workers in
metal might perhaps throw some light upon the subject.
The case of standard weights is involved; also spectrum
analysis.-M. PARIS.

-

[5292.] PERCUSSION ACTION FOR HARMO NIUM. "J. C. L." (p. 880) evidently does not under stand the percussion action. It has no connection one set of reeds (generally the flute) is struck with a whatever with the expression stop, but consists of an action similar to a pianoforte on a small scale, by which light hammer, making a sound similar to a harp, when the bellows are not blown. It was first invented with the object of making the reeds speak promptly, but is distinct variety of tone. A well-made harmonium will now retained for its peculiar character of tone, which makes it valuable as an accompaniment, and gives it a speak as quickly without the percussion as with it. I have never seen it on any English-made harmonium; and when I tried some time ago I could not get any of the English makers to undertake to make one. The hammers are thrown in and out of action by the percussion stop. The reeds ought to be made specially strong and good for this action, or they become faulty own instrument are twice as strong as those in the very soon. The reeds in the flute-percussion in my pressure of wind to make them speak freely if used without percussion.-T. F. musette or baryton, and require more than double the

[5463.]-PROBLEM (U. Q.).-1. Construction of the

A.

H

a

D

Figure.-Take the obtuse angled triangle A B C. At the point in the B triangle ABC with the radius C B, de. scribe the arc B H B', and produce A B to B, and join C B. In the straight line B B bisect it at the point D (Enc., I., 10), and at the point D draw D H at right angles It must pass through the point C (Euc., III., 1 Cor.). CDX AD to B B (Euc., I., 11), also produce H D to C. Area of the triangle A D C = 2 (b sin. A) (b cos. A)

- From "Bernardin." USEFUL REDUCTIONS. Weight of a leaden tube: D, d being the outer and inner diameters in centimetres (D+ d) (Dd) × 891 will give the number of grammes of a metre length. COMPRESSED PEAT.-Mr. John Blatchford, of 6, and the area of the triangle A B C be sin. A cos. A+ a b sin. A cos. B Salem-place, Newton Abbot, Devon, noticing the mention made of peat in our number for Dec. 16, 1870, has sent He has Therefore the sum of the areas of the two triangles us a "specimen of what he can do with it." 2. By the questionbeen engaged for many years past in the endeavour to A B C and A B C b2 sin. A cos. A. n (b2 sin. A cos. A a b sin. A cos. B) (b2 sin. A cos. A+ a b sin. A cos. B). utilize the millions of acres of peat in Great Britain, tors andothers that he can manufacture the compressed and wishes to state for the benefit of peat land proprie peat according to sample at a cost of from 8s. to 10s. per Divide by b sin. A and trans., ton. The specimen sent to us is an elongated ball About the mode or about 8in. by 4in. in diameter, weighing 18oz., and certainly has a very fair appearance. of production, or whether the specimen really has been By divisionproduced from peat, we can, of course, say nothing.

IMPROVED SPECTROSCOPIC PRISMS.-Professor Walcott Gibbs, of Harvard College, Mass., has experiCIRCUMFERENCE TO DIA- mented with various liquids as substitutes for bisulphide of carbon, sometimes used for filling hollow glass prisms METER.-CORRECTION. of 60°, Bisulphide of carbon is cheap, colourless, and [1252] IN letter 1202, p. 403, second paragraph, unites a moderately high mean refractive to a very high where commenting on the objectionable ambiguity of dispersive power, but it is very volatile, quite sensitive, odour. A solution of phosphorus in bisulphide of carthe symbols sin.-1, and tan.-1, I was led into an error optically, to changes of temperature, and has an offensive through not observing that there was a still further bon has a dispersive power 50 per cent. greater than The third proportional that of the bisulphide alone, but it becomes turbid on objection than I had noticed. exposure to sunlight from the formation of amorphous sin.2 a phosphorus. It occurred to Professor Gibbs that the formation of the amorphous phosphorus might be prevented by dissolving sulphur with the phosphorus, and experiment proved the correctness of the opinion. His practice is to dissolve one part of flowers of sulphur and two parts of phosphorus in four or five parts of bisulphide of carbon, and to filter the liquid through a well- than unity; dried ribbed paper. This solution gives a spectrum a marked absorption at the violet end of the spectrum. perfectly clear, but owing to its yellow colour there is The disadvantage in using it arises from the danger of breaking a prism, for the the liquid takes fire spontaneously when brought in contact for a few seconds with any porous material like wood or paper.

cannot be expressed, as I there said, by sin.(sin. a). This latter is different quantity, namely But if the sine of such an are as equals the sine of a. asing, as English mathematical writers do (but no foreign that I am aware) sin.-1 a to mean the arc whose sine is = a, we are bound to let "sin2 a" stand for one or other of the above quantities, and not the square of sine of a, while there is an ambiguity which of the two it may mean. For we may consider the index attached

n-1
n+ 1
(n
· 1) (n + 1);
(n + 1) (n − 1)'

we have

its value lies between the highest and lowest of
pqrs
; but the far from obvious and really chief part
a, b, c, d,
of the theorem, that it differs (in most cases) from the
mean of those four fractions, he has not touched. It
seems plain also that this latter is not universally true.
There must be some relations in their value, that will
make the long fraction equal? + ; and some other

2 a

R

2 d

+ ; and these

4 d

that will make it =
2 + 2 +
4 a 4 b 4 c
conditions have to be defined.-E. L. G.
[5573.]-WATCHMAKING (U. Q.).—If "Watchmakers"
will refer to the reply to query No. 5398 in the same
number of the MECHANIC in which their query appears
they will see the turnbench described by-TOMETER.
[5578.]-SHIPS FREIGHTS (U. Q.)-"N. T." must
State more, fully what he wants, for although I
have been a ship-broker for over 15 years, I am unable
to understand his question.-A. B. B.

[5615.]-MUSICAL BOX (U. Q.).-I should recommend "R. O. R." to shift the comb of his musical box a little further away from the barrel.-TOMETER.

[5620.]-CLOCK CHAINS (U. Q.)-If "J. B." cannot explain what he wants he cannot expect any one to guess, and therefore should not send such stupid questions to our MECHANIC.-TOMETER.

[5662.]-SECRET DRAWER (U. Q.).-You can have a drawer 15in, by 10in. by dovetailing the sides upwards into (but not quite to the top of) the piece you say is let in, as in. blocks are ample to hold the sides and front. If, however, you prefer the secret contrivance you can put two small pins firmly in one end, make holes in the sides for them to go in nicely, and have a small catch the other end inside, a wire from which to a nob in front can easily be made to open it at pleasure.-W.

[5675.]-CIVIL SERVICE (U. Q.)-"A Teacher" will obtain all necessary particulars at the office of the Civil Service Examination Commissioners, Westiniu ster.— A. B. B.

[5676.]-PAPER STUFF (U. Q.)—“Papyrus" isinformed that Esparto grass is largely used in the manufacture of paper, together with all kinds of vegetable fibres, straw, reeds, grass,&c. Both the newspapers mentioned by him, are, I believe, made from a mixture of esparto with other stuffs. I have seen, I may say, several hundred different kinds of fibres suitable for making paper pulp, and have been for some time busy introducing a new vegetable fibre for the wholesale manufacture of paper. -A. B. B.

[5688.]-WATCH CONVERSION (U.Q.)-The last English horizontal I converted had a train composed of 63, 60, 60, and 18, with three pinions of 7, giving 17,190 vibrations per hour. As the lever escape-wheels are not usually made with 13 teeth, and I should have had to get one cut on purpose, besides being obliged to make the the pallets myself, I put an escape-wheel of 15 with pinion of 8; it then gave 17,857 vibrations per hour. I usually take as the length of my lever the distance of the pallet staff-hole from the escape-wheel pivot-hole, when properly pitched. As this longth, with the ordinary escape-wheels and pallets, is nearly the distance of four points of the teeth of the escape-wheel, I took this distance as a rough gauge, and marked it on a piece of paper on two lines forming a right angle (it could be an obtuse or acute angle). One of these lengths represented the escape and pallets pitched off, and the other, divided into thee, and one of the parts added on to it, represented the length of the lever and half the acting diameter of the roller. I cut out the paper and applied the respective ends to the balance staff-hole, and the escape-wheel pivot-hole, or the distance it would be from the fourth wheel, to see if I should have to make a bar for the escapement, and found there was ample room without one. If a bar could not be dispensed with, it would cover the fourth and third holes; the third wheel arbor would have to be cut short, and pivot in the underside, while the fourth pinion would pass through, and that wheel would pitch into the escape-pinion on the upper side of the bar. -NOBODY.

[5694.]-METRONOME (U. Q.)-It seems to me that the metronome beats more slowly when the bell is acting than when it is not, because in the former case the spring having more work to do takes a longer time to do it. I have timed my instrument, and find that it beats the marked time without the bell; it is, therefore, somewhat slow with it.-BEACON LOUGH.

[5713.]-WELSH GROIN.-I am sorry I mistook "J. K. P.," but when giving the pronunciation as far as possible in English of a foreign word it is surely better to remember the consonants. "J. K. P." may be a remarkable linguist: ny Continental experience, not small, has induced me to doubt, whether any Englishman can acquire the foreign timbre. The German w

[6099.]

CENTRE OF GRAVITY OF A SEMI

2. 8

The notion of relief is arrived at through a process of reasoning from experience, and we should, therefore, ELLIPSE. "E. L. G." is no nearer the truth the image of the stereoscope is not in accordance with our altogether, after once mentioning it. Applying his me see in that case objects as we do now. experience, and therefore we are deceived into seeing thod we can get the true result thus.-Let d be the dis But the "J. K. P." He loses sight of the area of the hemispher objects more in relief than they are. The pseudoscope tance of C G of quadrant, from a boundary radias puts his error in judging relief in a very clear light. Then if quadrant rotates round that radius it generate By merely changing the direction of the shadows thrown by an object we take it to be not in relief but hollowed a hemisphere whose volume is out, and any method of suddenly reversing a shadow nus's properties we have the same volume area of qu will produce the same effect. "E. L. G." therefore will rant multiplied by length of path traversed by CG But by Gald see that his lesson on rudimentary perspective, otherwise so valuable to a person in my profession, is thrown away. I am under au impression that some such an arx 2 d. Hence rangement as that which gave rise to this question can be purchased, but upon that matter I offered no opinion although I had my own. being in wrong perspective was an obstacle, all stereoI merely pointed out that if scopic pictures were necessarily already in wrong perspective. I make no comment upon the rest of the comthe places they hold in nature, and if we make them apmunication of "E. L. G.," as needless. Perspective is the art of representing objects and parts of objects in pear to "come forward" more than they ought our perspective is too good to be true.-M. P.

TYPE(U.Q.).-Process, Becquerel with galvanism. Attach
[5726.]—BECQUEREL'S COLOURED DAGUERREO.
a clean daguerreotype plate to the+pole of a | without
immerse both in the exciting bath, having previously
galvanic battery. To the wire fasten a platinum foil.
well isolated the copper back of plate with varnish. The
plate is soon covered by violet chloride of silver which
then passes to black if the galvanic action be con-
and slightly rub with cotton wool, to rub off a sort of
tinued long enough. Now stop the action, wash plate,
fog. The plate is now ready for exposure. The thinner
the film the shorter the exposure. The thicker the more
vivid the colours.-W. BRICE.

be preferable.-DELATEUR.
[5733.]-LAMP (U. Q.).—A sp'rit-lamp, or gas, would

[5741.)-PATENTS (U. Q.).—"J. M. W." can apply
should he apply to some respectable patent-agent to
personally for Letters Patent, at a cost of £25; or
carry it through for him, the cost would be from £35 to
£40. Apply at the office of the Commissioners for
Patents, Southampton-buildings, for a copy of the
give him a very clear insight as to his proper course.-
"Patent Law Amendment Act," price'6d., which will
A. B. B.

or rather the elements of Dis the frame pivoted at o,a revolving in the circular trane F; G is a lens, not requir absolutely; H a glass plate. K a glass plate pivoted at L is the plane mirror; the whole. of course, mounted as usUA When the frame D is parall to that of K the field of sight dark; but here I must ques the German text as it scand for fear of mistakes, and you spiegel K, so ist bei Hindurchsehen durch die Glassplat translated as best he can:-"Macht dagegen die E correspondent must get a flexionsebene des Glassplattensäule einen rechte Winkel mit der Reflexionsebene des Polarisation

K

ten das Gesichtsfeld hell."-W. BRICE.

(GO52.)-THE GUN LICENSE.-I am sorry to dif beg to [3787.]-ALUMINUM AND ITS ALLOYS (U.Q.).—I requires no 10s. license, as he argues very neatly, from J. B. Primus's" statement that an air-gun caric send the following extract from a small their Properties work, recently published by Longmans, entitled "Metals and in proof thereof two men were summoned by the E the fact is the new Act does include air guns implied, Bloxam, hoping it may be of use to him. facturing objects of ornament from aluminum a soldering the new Act.-B. H., Solicitor. and Treatment," by Professor cise officer about a fortnight ago at Croydon for carry is employed which contains ninety parts of zinc, six ing one without a license, and a fine of £3 was inflicted of aluminum, and four parts of copper."-HOUBLON. Your correspondent I think has argued without read

with liquid ammonia is probably the one referred to.
[5894]-FREEZING APPARATUS.--Carré's apparatus
invented by, I believe, a Mr. de la Rive. At any rate
But one which appears likely to supersede it has been
full i formation could be obtained by writing to the
Gourgas, 113, Plainpalais, Geneve, for there it was that
Société Génèvoise d'Instruments de Physique, Chemin
the mach ine was made and experiments conducted.ments cannot go for any length of time with "absolute
[6056.]-OILING CHRONOMETERS.-These escape
soak in. With this, for a pallet that is not jewelles.
in the oil, and wipe off the superfluous oil that does
no oil," but at all events, the great aim is to give as litt
touch every other or third tooth of escape wheel, atu
as possible. The usual way is to dip a point of peg-wood
when jewelled only the pallet itself.-NOBODY.

W. BRICE.

with holes 1in. in diameter, and, as soon as laid, place
[5941.]-PRESERVING EGGS.-Have a plank drilled
the eggs in these holes, small end down, till wanted. By
this means I kept them fresh in Ceylon, for a fort-
night or more.-W. BRICE.

given to me by Professor Dr. Edouard Clapparède, of
Geneva :-Hydrate of chloral, 8 grammes; water dis-
[5967.]-CHLORAL HYDRATE.-Here is a form,
tilled, 15 gramnes; a teaspoonful in a glass of wine or
beer.-W. BRICE.

five different trains to the length of the half-seconds
pendulum, which is 9-800in. The best train is 80, 80, and
[5993.)-HALF-SECONDS PENDULUM.-Reid gives
36, with two pinions of 8. The centre-pinion counts
with the teeth in the wheel on the barrel, and how
many turns that makes, and if necessary with an in-
termediate wheel, to tell how long the clock will go.—
NOBODY.

spring gauge are to tell what diameter of spring a barri [6062.]-WATCHMAKING.-1. The circles on a mais of a certain diameter will take.-2. Watch wheels arr not exactly fixed in the turns to drill for a new pivot, but unbroken pivot works in a centre in the turns, while the a ferrule is fixed on the arbor (if it has any) on the side of the unbroken pivot, if not, on the wheel itself. The wheel, and enables the winder to turn either way. The drill is supported on the T rest.-8. There is a spri mainspring is held in one hand while the other works fixed on the spring-winder, which shifts from one side t the other to make either click work in the ratchet the spring.-NOBODY. the crank handle. When the spring is wound up, the latter takes hold of the spring and relieves the other which is at liberty to take up the barrel and apply it to

rough tracings from "Le Manuel du Tournear" of 80:e [6063.]-SWASH PLATE TURNING.-I inclose seme of the apparatus required for oblique turning, the rest of which is to my mind rather curious than gracef

has been called a flat English v; also it is said to be the Ployed in mixing the mortar or cement; but that for the (see next page.)-G. C. C.

same as the v of France, Spain and Italy: is not circumflexed-it is often a short diphthong; the two dots have been by some thought to be a modification of the superposed e, but Adelung differs. I never noticed in Germany anything very different from our v in their w, and I am a tolerable musician.-M. P. [5715.]-HEATING CIRCULAR CONSERVATORY (U.Q.)." P.P. W." will find hot water the best, the cleanest, and most efficient heating medium. The pipes can be placed either above or below the floor, and if it is not convenient to have the boiler close outside the conservatory, it can be placed in any outhouse near, but the farther it is off the more expense in fitting.-UN

JARDINIER.

[5716.]-STEREOSCOPIC LENSES.-I think I perceive into what error "E. L. G." has fallen: it is confusing two photographic pictures with their stereoscopic image. The photographic pictures I will, for the sake of argument, concede to be in true perspective, but if they represent the scene or object as observed in places more than an eye's length apart, their combined image in the stereoscope must be in exaggerated and therefore wrong perspective. The magnitude of the separate photographs only affects the apparent proximity of the object. Stereoscopes are constructed with magnifying glasses, and moreover, in the original stereoscope of Wheatstone, one of the very first now being before me, if not the first, the photographs can be made to approach or recede. It is certainly true that if we had eyes 3ft. apart we need not see objects in wrong perspective, but then the relief of an object is not a mere optical matter.

description of the construction of the Wolf Rock Light-
house, read by the resident engineer to a scientific
[6017.)-SALT SEA SAND.-In a recent technical
built solid to a considerable height-sea sand was em-
meeting in London, he stated that in all the lower
courses of the masonry in the base of the structure-
selected grit from the tailings of the stamps used in
crushing the tin ore at a mine in the vicinity, was found
upper and middle portion of the tower, a fine sharp
to be the most advantageous material for the purpose.
This statement, therefore, supports the evidence of
"J. B. Primus" relative to the construction of seawall
at Paignton, South Devon.-P. F.

hints on the above may not be amiss to "Tidal Works."
Salt sea sand, or salt water, I believe to be of no im-
[6017.)-SALT SEA SAND. - One or two practical
portance to the strength of the concrete provided the
sand is composed of silica (silex, flint), or as near to it as
possible. Clear Thames sand is good for any kind of work,
or any sand from the gravel pits in and around London'
concrete mortar, composed of Portland cement and sea
water sand a few months since in Devonshire, and found
well washed from particles of clay, loam, &c. I examined
it exceedingly hard, more so than any oolitic stone I ever
used. I have found that Portland cement is far more
satisfactory if laid on in one coat only, and then
smoothed off.
good materials, should be one to four or five; for con-
The proportion of cement to sand, if
I have discarded of late years. In Devonshire, on the
crete foundations one to six or seven.
sightly for exterior dressings and stucco. If "Tidal
sea coast, it vegetates more or less, and becomes un-
Works" tests his cement before using he will find it
safer.-W. A. D.

Roman cement

other side of the earth if more influenced always by the
[6038.)-SHOOTING THE MOON.-I beg to thank
gravitation of the sun.-M. P.
"E. L. G.;" my difficulty was how the moon got to the

44

the tool a pivoting tool, as it is quite different from the
[6093.]-SWISS PIVOTING TURNS.-I must refe:
Young Jobber" to my description of the Swiss ture-
bench in reply to query 5308. He is mistaken in calling
"tour à pivoter," which is only made for the purpose of
clusively by continental watchmakers; English work-
making pivots by means of a file, and is used almost ex
men prefer to turn the pivots with a graver, between Le
centres of a turnbench. I will make drawings of both
tools if the Editor thinks them worthy of space.-
TOMETER.

WOOD CARVING.

Having sketched pattern of anything you fancy to Lal[6104.]-FRET WORK AND proceed to cat with bow saw. My smallest is 6in., and tate in fret-cut brackets, book stands, trinket stands, very fine, cost about 2s. 6d. with frame. Many an atospicture-frame corners, &c., fix your work in a vice, and teur in carving began with a penknife, and got chisuls upwards according to size. (See Ebonizing, p. 211.) and gouges, parting tools, &c., costing from a few pence quantity of the second added to the first. Brown amber To imitate rosewood stain with the first preparation as in the above, and imitate the grain with a small and beer make a very good walnut stain.-U.

SAND CASTING."A Subscriber" asks a question [6119.]-BLACKING FOR LOAM AND GREEN bag, and either print with his pattern, or blow ail off will give him a Lint or two. If his greensand castings which would require a treatise to answer fully, but I are light, let him dust finely ground charcoal on with a again he can with a pair of bellows, or if he has fiat