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= power of wheel in horse-power. Say 21 horse power. At* "Miller" has not given the area of the stream it is assumed as 4 x 1*5.—Stüdioba.

[4652.]—TONING BATH.—The following I have constantly used, and found to give satisfaction, producing from black to bright sepia tones, according to length of immersion :—Take carbonate of soda sufficient to cover a threepenny-piece; dissolve it in a teaspoonful of cold water in a cup ; add 2 grains chloride of gold; then add 8oz. of boiling water; nee in 15 minutes. After toning, pour it into a stock bottle, adding apartide of aoetate'of soda to give it keeping qualities. The next batch to tone, commencing in same manner, but using half the above quantities. Add it to the stock and tone immediately, and so keep on, omitting to add the acetate of soda, which should be added but once in twenty times. As is well known, one formula will suit one paper but not another. I never knew this to fail with Hart's alb. paper. —pero.

[4Ô52.] — TONING BATH. — I must refer John Terrae, as I have others, to my formula in a back number. It U certain in its working, which can properly be said of no other bath—that is, in every one's hands.— Mus.

[4652.]—TONING BATH.—If John Terras had stated what toning bath he uses, and the kind of tones he wishes to produce, it would have been easier to reply to his question; but he will find the old acetate of soda bath as trustworthy and uniform as any.—

DfDALBB.

[4652.]—TONING BATH.—Dissolve 25 to 30 grains of crystallized phosphate of soda in Goz. distilled water; then stir in 1 drachm of distilled water containing 1 grain of chloride of gold. Immerso the prints, which after removal from the printing frames have been well washod in common water and then dried. Five minutes in the toning bath is generally enough. Futher particulars and other formube on application.—T. Wyeh.

[4652.]—TONING BATH.—For Rive paper try the fol lowing :— Acetate of eoda, 6 drachms; dissolve in 6oz. of water. Borax, 2 drachms; dissolve in Goz. of water. Mix the two together, and add chloride of gold, 15 grains, dissolved in 12oz. of water. Pour the solution of gold Into the acetate aud borax solution slowly, with constant stirring; use next day. It «ill keep in good order with the addition of a bath made in the same way, using onlv one-fourth of the water, so as to keep up the strength. For Saxe paper:—Chloride of gold, 15 grains; water, 2oz.; precipitated chalk, loz. Mix in a jug, and pour boiling water, 80oz., over; stir, and let it settle; pour the clear liquid off, and add saturated solution of chloride of lime, 8 drops, and uso. It will keep, and may be strengthened by adding a strong solution made the same way. As these two baths arc used by me, the latter one in an establishment turning out some thousands of carte pictures per week, they can be depended on as giving first-rate results.—Operator.

[4655.]—MANGANESE BATTERY.—I should recommend " E. H. B." to Bolder each element of his batteries to a piece of stout copper wire a foot or so long, and then on the ends of these wires he had better put the terminals, which will not then get corroded. I believe the cause of corrosion is the vapour from the fluid in the cells.—T омет E в.

[4656.]—GOLD COIN.—It is an ancient British one, coined about 200 years B.c. I have a similar one In my collection, found at Brighton last year. The design on one eide Is meant for a horse. The value is about a guinea. Would Mr. Hoad kindly send me impressions in sealing-wax of both*sides of the coin, with his address? —Henry W. Henfbet, M.N.8., &c, &c, Markham House, Brighton.

[4668.]— BRAKE PIECE.—In replv to "Tometer" the cheapest commutator to make is tins : A A two strips of thin brass with connecting piece e, like a parallel ruler.

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N, !'*, N, three studs connected as the letters indicate with the negative and positive poles, then as the parallel strips are moved from left to right, or rice verm, the screws and consequently the connections underneath them become positive or negative.—B. N.

[4664.]— PRESSURE OF WATER.—In replv to "Holbeck " it may be stated that the pressure at the bottom of the two pipes will be equal, since, by the well-known law of the pressure of liquids, the weight or pressure of a column of water is proportional to its height, and is exerted equally in every direction; therefore, although oue pipe is, for two-thirds of its length, 8ln. in diameter, yet the pressure at the bottom of the pipe, 4in. only in diameter, will be as if the pipe had been iin.in diameter throughout its whole length. The pressuro at the bottom of both pipes, due to a column of water 12ft. in height, may bo stated (roughly) as 5lb. per square inch. —S . . . . в.

[4665.]—SOLUTION OF PROBLEM.—Let x = length of line in miles* y »= miles per hour the train ought to travel. Then (a) we have the following equations:—

X 6 z ¡I

(which becomes, when reduced to its simplest terms,

x « 5 ¡/), [A]

und,

* + 1í-ié + i + r-^iU

(which aleo Ъесошеч г 5 ц.) These results, being identical, show that the problem is Indeterminate. Tho reason of this is that the speed of the train is not given. The speed being assumed at pleasure the length of tho line will bear a fixed ratio to it, which ratio (from

equation A), is — = 5. Thus if the assumed speed be

40 miles per hour, the length of lino will bo 200 miles; if 20 miles per hour, 100 inilos, Ac. And (il) gives the following equation :—

which loads to the same result as before, viz., x =5 y. The enunciation therefore of tho facts, altered as supposed in the problem, would bo true; but it would not suffice to determine the absolute length of the line. As in the former cases we could only discover from it the length of the line relatively to the speed of the train.—R. Bennett.

[4607.]—CLEANING GUN BARRELS.—In reply to "Needle Gun's" query I certainly don't recommend the use of fine emery paper for cleaning the inside of gun barrels every time they get dirty (there is nothing for that purpose so good as hot water and clean tow), hut to clean off ail rust, Ac, that may have accumulated in barrels that have been put by for a time, and to make them look as clean and bright as on the day they left the gunsmith's shop.—Muzzle Loader.

[4678.]—INDIAN COIN.—It is a copper coin, struck in Euglaud for the use of the English settlements on tho island of Sumatra. On the left hand side of the engraving (p. 574), is the following Inscription in the Malayan language :—Baa Kepeng, 1247. This denotes the value to be two copper cash, 400 of which are equal to a Spanish dollar, formerly the general currency of the Eastern islands. 1*347 is the Mohammedan «bite.— Henby W. Henfrey, M.N.S., &c, Ac.

[4675.]—GOLD FISH.—You need not protect them, they will live through the winter.—С. В.

[4675.]—POND FOR GOLD FISH.—I have kept them alive and increasing in weight for several years, without protection, until they attracted the attention of poachers aud found the road to London. No pond should be without shelter of some kind, old stumps of trees, hurdles, Ac., and the banks planted with water plants. I»olepit gracilis is at presenta great favourite in Covont-garden. —En о Bave в.

[4676.]—NITRATE OF SILVER.—I should decidedly recommend " Paddy " to soml Li- precipitate to some respectable refiner and get nitrate of silver in return, for to do it himself would be more trouble than profit; but if he likes to try', hero is tho way to do it: Throw the precipitate in a* filter in a funnel sufficiently large to hold twice as much, then wash with hot water until the precipitate is free from all eoluble matter, then dry in an oven, powder well, and mix with twice its weight of a mixture of carbonate of soda and carbonate of potash in equal parts well dried; put it in a crucible and expose to the heat of a blacksmith's forge until the contents of the crucible are perfectly liquid; let the crucible cool, then break it and separate the button of silver from all traces of slag, dissolve the silver in an evaporating basin, by a mixture of equal parts of pure nitric acid and water, avoiding all excess of acid, heat will be required; then evaporate down to dryness and fuse the dry residue, taking care to use no more heat than is absolutely necessary. The fu<cd silver, if the operation be properly done, will be purely neutral and lit for any photographic purpose.—Operator.

[4880.] — BLEACHING BROWN CALICO.—If "N3" will first boil the calico in lime water, wash, and without drying boil again, in a solution of soda or potash ; wash, aud without drying steep in a weak mixture|of chloride of lime and water for six hours; wash and without drying .steep for four hums in a weak solution or mixturo of sulphuric acid and water; wash well and dry; he will find In calico white, sound, and beautiful.—Wausrof.

[4682.]— TONING BATH.—I will look out the number that the formula appeared in aud let "Photographer" know which it is.—Mes.

[4683.]—VALVE FACINGS OF CYLINDERS.—The cylinders always have tho valve facings cast on them: they aro finished by being turned, and the parts that will not run true are filed as best they can be. I think borax is the flux for brass. Will "Amateur BrassFounder" kindly describe his furnace for the benefit of hisbrother readers who will gladly receivethe description, at all events I Bhall be extremely obliged ?—Tometeb.

[4684.]—TYPE.—There is a decided and palpable difference between "genuine" and "pirated" type, as there is betweeu an original woodblock and its cliche. Any typefounder would point out the distinction practically in a minute better than word painting would tell in an hour. Weight for weight, I should prefer the "genuiue," but I never heard of any positive trial as to duration. In metal of equal quality much difference may be produced by the manner of casting.—Engraver.

[4689.]—PEDOMETERS, DESCRIPTION OF.—The following description of a pedometer, the invention of a. Mr. Payne, is extracted from the Magazine of Science. "In this extremely ingenious and skilful contrivance motion is communicated from the traveller to the machinery of the pedometer, by means of a horizontal lover, which is furnished with a weight at one end and a pivot or axis at the other; under the lever is a spring which keeps the former when at rest close up to a regulating screw; the spring being so arranged a* to bo only just sufficiently strong to overcome the weight of the lever, and prevent its falling downwards. When the body of the traveller is raised in progression, tho lever is impelled downwards by the jerk, and immediately returned to its place by the spring, and so long as the motion is continued, the lever is constantly in a state of vibration. A small ratchet wheel is fixed to the axis of the lever, and beneath it Is another and larger ratchet wheel, which fits on the same axis, but is not attached to it. These two wheels are connected by a ratchet or pale iu such a manner that when the lever falls both wheels are moved forward one or more teeth,

but when the lever rises again from the force of the spria? the larger ratchet wheel is held stationery bv a ratchtt The larger wheel is connected with a s*riei of tooth&J wheels and pinions, by means of a pinion fixed on iu under-surface. The centre wheel carries an index or hand, which points to figures on the dial-plate."—S ... i

[4693.]—BICHROMATE BATTERY.—The distan» between the plates should be as little ал possible, £iv Jin. ; the copper wire can either be soldered direct into the carbon or a terminal soldered in tir-l, and the wire clamped by means of the screw. The soldering muitbe done carefully to ensure A good connection; drill i good deep hole into the carbon aud nil it with soft solder, using plenty of soldering fluid, put tho екча wire or torminal into the hole hot,—Toxeter.

[4*94.] — HOROLOGICAL.— I canuot understand wbit B.E. Loddy means by the first portion of his query; is it a misprint? The sizes of foreign watches' are reckoned by lines and English watcher run by u.^s, thus :—8, 10, 12, up to 24. which is the largest ем in general use ; No. 8 size is the smallest.—Tómete*

[47D1.1—CLEANING COINS.—To clean copper ecani, scrub them, and then lay them in dissolved sulphaW copper (a super-s atura ted solution), for я few beam, then brighten with a brush or leather. Silver couv.fibe cleaned in the fame manner, by neing nitrate d silver.—С. В.

[4701]—CLEANING COINS.-Put them In it-' lntion of one part of acid sulphuric and fon г of waterf: a few minutes, and then rub well with a piece 4 chamois leather; they may be kept brigfat by grri« them a coat of collodion.—G E оме твоя.

[4708.]— CHANGE WHEELS.—I don't think the»« rule that would answer his purpose, only what; ist£d the rule of thumb. If you can tell how many bp</ roving (of a Gertain hank) it will take to All from ев end of the bobbin to the other, and then calculate u* speed required to run with the wheels you have on (fiie¿ by the maker), and by the following general rule fee speeds. Multiply the speed of driving wheel by the intermediate driving wheels for a division; then the required speed by the driven wheels for a dividend, tae quotient will be the wheel required, for lifting or copy. For ratchet wheel the following will be the only means that I know of (I take it for granted that you know the general rules of cotton calculation): the two extremes of the cones give the speeds for full and empty bobbins. II you know how many laps of a certain hank will nil a bobbin, you may then find how many teeth then? is in the ratchet by the following simple methods. We will suppose there are 60 laps on a bobbin and a fixed wheel on the shaft (that carries the ratchet wheel) which makes three revolutions; in moving the strap from oue end ol cones to the other, it will require 60 movement* ot ratchet wheel to fill the bobbin half a tooth each time; divided by three, the number of revolutions to move it to the end will give ten, the number of teeth required; and in answer to the other I don't fully understand which wheel he means.—В. H., Rochdale.

[4704.]—CHANGING SURNAME.—The usual pUn now, I believe, is to advertise your intention in the le ading newspapers. A few years since many lottere appeared on the subject, when Mr. Jones took the name of Herbert, and Mr. Bngg that of Howard. Cousait Palmer's index to the Time* newspaper.—Ax Old Man.

[4705.]—NATURALIZATION.—There isa department called the Alieu Office, either at Whitehall or at Downing-street, where application should be made, &nd the proper forms obtained.—As Old Mam.

[4706.] —PHOTOGRAPHY.—"In в Fix" has mostprobablyadded too much salt. It is a fact frequently forgotton that chloride of silver is far from being insoluble in a strong solution of salt. Let him add some strong silver such as an old bath, and after stirring it will settle clear. For the future use as little water as you can for washing the prints, as the weaker the solution the longer time it takes to settle, and instead of salt use hydrochloric acid to throw down the silver, it will answer much better. About a dram or so to the gallon of washings will be sufficient.—Operator.

[4706.]— PHOTOGRAPHY.—Let "Ina Fix" expose the water to sunshine for a day or two after putting iu the salt, he will be sure to have a precipitate then; that is, if there is any silver at nil in the water.—Mes.

[4706.]—PHOTOGRAPHY.—Allow me to suggest to "In a Fix" that perhaps his exciting bath has got very weak, во that his prints contain little or no free nitrato of silver, because if any Is present iu the washing water salt Is certain to precipitate it.—D.ïdaj.us.

[4707.]—STEAM.—The best rules for treating thi* difficult question will probably be found in Rankim > works, as his " Useful Tables and Rules," page 302, iv-E. L.G.

[4710.]—TO REFASTEN BRASS TAP IN KITCHEN BOILER.—Obtain a epanuer to fit the nut mùd* the boiler first of all; turn the loose tap towardt t-Ht left, then place spanner on nut inside; hold tight, tben turn the tap back until it becomes firm.—CaUfAx.

[4710.]—THE BOILER TAP.—" Inquirer" wfll find inside his boiler a screw ferrule on the shank of the tap, which he must screw up tight with some red lead iu the j oint.—Geometroh.

[4710.]—FASTENING TAP IN KITCHEN BOILER. —Hold the nut inside the boiler with a spanner, while you turn the tap round outside with another spann rr until it is tight enough. Should the tap be not upright when thus tightened, unscrew and back tap and nut sufficiently and screw up again. Sheet-lead for washtr is perhaps the best.—G. F.B.

14718.1—BEES.—I should advise "J. G." not to remove his bees till the spring, as the combs will then be full of brood ; the better plan would be to let them s warts and put the swarm where they are to remain. The hole in tho wall should be Sin. or ¿in. wide; the bees will b* виге to find it if placed there the day they swarm. The best food is lump sugar and water in the proportion ol three of the former to one of the latter, boiled till dissolved. A common pickle battle filled with this, and a piece of cap net tied over the top and then Inverted over a corresponding bole In the top of the hive is th»best way of administering it. Bees should have all the food they require for the winter given to them during mild weather, as if it is too o*ld for them to take wintr after taking food they are very subject to disease. If

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affinity of sodium for chlorine is greater than that of
zinc- let us express this by figures, which are, it must
be understood, purely arbitrary, and used simply to
convey tho idea. Expressing the attraction of zinc by
40 and that of sodium by 6U, we see that the zinc can-
not break up a molecule of the salt; but, formulating it,
Sa, C1-. x Zn, we readily conceive that tho internal
affinities of the salt are weakened, that the molecule is
held together by a residuary force of zO only, and is
thus " polarized;" it only requires, therefore, some other
force to complete tho rupture. In the manganese battery
this is supplied by the readiness of the extra atom of
oxygen to enter into a now combination, and as a result
°f tho several actions which take place on the line of
polarized molecules, the sodium is transferred elsewhere
and chloride of zinc formed. I think Mr. Jarinau is
mistaken as to the iron. I have seen cast-iron long
buried i, is- into such a state as to become soft and have
■•reat excess of carlitu. bnt ordinary cast-iron contains
only from 3 to 6 per cent, of carbon, either as graphite or
combined.—Sioma.

., > > 1—a ARIETIS.-I do not think a Arietis can be seen with a Sin., unless the observer possesses altogether except oual powers of vision. If 1 remember rightly I describe it in my " Half Hours with tho Telescope," as a verv difficult object for such a telescope. A sharp-eyed riend had seen it with such an aperture, or told me so and it is to be remembered that seeing minute points of light depends quite as much on eyesight as on the telescope. If 1 did not believe this I should have to regard OTme esteemed friends as untruthful, for they see object, which are not only wholly invisible to me with the same telescope, but commonlypregarded as whoUy beyond the power of such telescopes. The position angle o . ArEtl. is about MP, B of about 10th magnitude, and purple, distance is considerable, and IS is triple.— ItlCllABD A. Pboctor.

r4731.l-CARBONS.-The process given by mo for protecting carbons and their connections does not at all affect the conductivities, I carefully tried that point before nubUshiug the process; of course it will destroy conductivity atf the surface, that is to say, the reception of the current; though if we'll rubbed so as to clear off any film of parafflne current will pass into it from metals to considerable degree, but of course not from liquid because they do not come into real contact with the carbon.— SIOMA.

!47S->1—GAS TAR.—I am not acquainted with the process", and should think a preparation of carbolic acid likely to be moro useful and much pleasanter.—HIOMA.

(4733 1—BRONCHITIS.-" Omega" is surely mistaken
when ho describes his symptoms as "bronchitis.
Bronchitis is an acute inflammation of the membrsnes
ol! the"bronchia, or breathing-tubes, and 'f »"acked
with it he would not be able to walk about long.
^Omega's " ailment is evidently ehronu, and the fact of
the mucus being streaked with blood is an extra reason
why he should seek medical advice at once.—Haul

[4738.1 -GEOLOGICAL-Tho question of "Veritas"
is one I believe must unaccountably shelved by our pre-
sent geologists. The only theory I have seen ever
attempting.t was by a Follow of the Dublin Society;
that ki the frequent and tremendous dislocatory earth-
uuakes attested by the " faults" or dykes of those early
steata each of those dislocations or cracks through the
whole earth crust, down to the very lava level, acted as
a ill ,-riuding and shooting forth upward clouds of its
ovra milverised rock, which, diffused through a ya.t ex-
tent o overlying sea, then settled on its bed, forming
wh"t has, under intense pressure, for tUou«nd. of
Jges, accompanied in many cases by bakingl heat, now
become a thin bed of sandstone, shale, or clay. n»
uonienn feebly representing this aro ""own even in
some modern earthquakes, as the last great Permian
one a dark and stifling cloud of dust being suddenly
miffed up from a new crack into tho air. Now the ex-
tent o" rub or "downthrow" in these, dislocations is
rarelv Ureeptible or noticed. Say it| is inches-what
hen u list have been ground and shot forth by tho ninety
Xm"ault the Cleveland, or any of ^ Innumerable
great fault, that dislocate our elder strata in alljliree-
w01l the miles of crust thickness were thus
wrenched through in tho throes of the earth's infancy
H coal beds be now preparing about.the great ropical
river mouths, that pour down a yearly tribute of forest
sooils there must be very thick uniform deposits, as
Such MTas the Nile alluvium, the London clay or chalk.
The oW strata, with their countless dist net.beds rarely
yielding a stone a yard thick, and continual changes ol
ma edal-a foot o'f this, two of that, so n»hy>ncb.e»
deep rod sandstone, one inch pale buff, and then the
dee red again-these indicate a widely different state of
nature from any now known; and I agree with that
Msh geologist that it is utterly inconceivable the bulk
o hose ever changing sediments were over derived,
like the tertiary or alluvium, from the ram andnver
wash on ancient* lands, as it is now the English fashion
to assume.—E. L. G.

r4740 1 -CONTACT BREAKER.-I believe the con-
tat breaker of the Polytechnic coil is a modification, of
Foucault's. A stout glass vessel is per orated at the
bottom and a large platinum wire inserted, a layer of an
amalgam of platinum is placed in the vessel and covered
teraevenl inches deep with tho strongest alcohol. On
the ton of the vessel is a fitting exactly hke the rod of
the b chromate ceU (in fact, the apparatus is made from
a bichromate battery), with a spiral spring added^to
Sustain ?Se rod, the extremity of **kh»'TM£,"££
largo Platinum knob. To make contact, the rod lsae
nr?ss?d till the knobtoucl.es the amalgam; to break

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sumed,Is a good deal of trouble was experienced at first.

"uT^Hl-GUN-COTTON.- "Experimentalist" does
former from his adding no water to his acids , i[s»,tne
v^m^?strong siUphuric acid; then^the cotto. isl.n

acid, it is dried and the matted parts pulled out with the lingers or a pin.—P. B.

[4744 ] — GUN COTTON. — Take of cotton loz„ sulphuric acid, 5 fl. oz., nitric acid, 5 fl. oz.; mix the acids in a porcelain mortar, immerse the cotton in the mixture, and stir it for three minutes with a .■lass rod, until thoroughly wetted. Transfer the cotton to a vessel of water, stir well with a glass rod, decant the liquid, pour moro water on the mass, and repeat tho process until the washing ceases to give a precipitate with chloride of barium. Drain the product on filtering paper and dry in a water bath.— W. F. L.

(4744.1—GUN COTTON.—Mix 4Joz. of pure, dry, nitrate of potash with SO fluid drachms of sulphuric acid (so gr 1-815), ami stir into this mixture carefully 130 grs. ol best carded cotton. As soon as saturation is complete (in about one minute, if proper care has been used), throw the cotton into a largo pan of clean ram water, and change tho water repeatedly untd litmus ceases to show the presonce of acid, then squeeze it in '-,_n. „_., ..,.,. i,ninn vail nulled nut. drv it at a teui

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to make gun cotton lor some years, but I am pretty certain that I have tried the above, among many other., and found it suitable for photographic purposes. Nitric acid is sometimes used in place of nitrate of potash, though I think the latter is preferable—T. W.Boobd.

(47441—GUN COTTON.—One part of finely, carded cotton is immersed in 15 parts of a mixture of equal measure, of nitric acid, of specific gravity V52, and sulphuric acid of specific gravity 1845 The cotton 1.111 »t be completely immersed in the mixtnre, otherwise it becomes so hot as to uudorgo instant decomposition. \fter a few minntes immersion it must be plunged into 'a largo volume of cold water, and then washed so long as the least trace of acid is perceived, when the moist mass is placed upon litmus paper It isithec1 to be oarofully dried at a temperature below 212° Fahr. When prepared for military purposes it is found advisable to prolong the immersion in acid for forty-eight hours, and to continue the washing for several days. As thus prepared gun cotton scarcely differs from unchanged cotton in appearance; it i. white and fibrous, and rather harsh to the touch.—Oxoniessis.

[4752 j— DIFFERENTIAL CALCULUS.— By formula

* (i)
dtt _ 0- (s) * (1) - »' t» *JJl

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centro to centre, is sufficient for amateurs' lathe*, and affords room for strung hole*—¿.f., that will take a strong peg. Aud the holes should be drilled with a taper drill aud have я peg that fits accurately. I have net yet schemed my model division peg or "alidade," but shall shortly, and communicate the same. Those in common use are abominable.—J. K. P.

[4779.] — HOLTZ' ELECTRICAL MACHINE. —" A Revenue Officer " (p. 599) will find the Holtz machine explained with detailed wood-cuts, in the English Mechanic, Vol. III., p. 170. In French, description with wood-cuts is to be found iu Le* Munde* (L'Abbé Moiguo's), Vol.XV., p. 4S9, also in Ganot's ''Physique," the last cditiou, tho 18th. Poggendorfs improvement of using a" full " fiml rir.e with small holes, is mentioned in Let Monder, Vol. XXII., p. Я01. The latest change proposed by Fr. Proveuzoli, of the Кошап College, was announced and explained in a Roman journal of last May.—E. Kernan.

[1779.]— HOLTZ'S ELECTRICAL MACHINE.—A description is giveu in No. 226, Vol. IX., p. 391. Several modifications nave been made latoly, and several essays and papers on the subject published in Germany, but" I am not acquainted with the particulars.—Sigma.

[4779.]—HOLTZ'S ELECTRICAL MACHINE—In reply to" A Revenue Officer," he will find a description of Holtz's electrical machine in Gauot's " Physics," page 616, edited by Atkinson, published by Longman. Also in Brooke's " Physics," page «90, published by Churchill. —В. T. N.

[4781.]—SUSTAINING BATTERY—I do not know vf hat is the special' battery referred to; from the description it may bo tho sulphato of mercury, as in this mercury does collect: but an ordinary Daniell's or a sulphate of lead battery would do If considerable force of current is needed ; or a manganese or mercury cell, if merely signal instruments are to be worked. The period of working would, in any case, depend on the arnouut of work to be doue iu any given time ; it is qnitc impossible to name any time without knowing this.—Sigma.

[4785.] — BINDERS' TOOLS. — I cannot inform "L. J. W." where he can obtaiu a pattern book. Has he applied to Timbury, 101, Fetter-lane, E.C.? I have never given any recipes for staining leather in " oui-" Mechanic, but if he will state iu tho next number whether it is white calf he wishes to colour, and the particulars, I shall be uiost happy to give him the desired information.—Ad Initio.

[4786.]—IMPRESSION OF FERN LEAF.—Well oil a piece of paper (say note pnpor) with linseed oil, hold it over a smoky flame, snch as that given by a tallow-candle with a long snuff, moving it about so as to evenly black it all over, place it on a smooth surface and lay the feru leaf on it; over that place a common piece of paper, rub the hand well over the part where the leaf is, remove the paper and place the leaf, tho blacked side downwards, on the paper to receive the impression; place over this another picco of paper, rub the hand as before and on removing the paper and fern an accurate impression will bo found upon the paper.—P. B.

[4786.]—IMPRESSION OF FERN LEAF.—I have found the following way answer very well. Take a sheet of note or other paper,'grease it on one side and then hold it over a lighted candle, so that the smoke blackens the greased paper, when well blacked place the leaf ou it, press it well and then transfer to a cleau sheet of paper, after pressing it some time it will be found to leave a very good impression.—Fkancesa.

[4786.]— IMPRESSION OF FERN LEAF,—Roll the leaf carefully with a printers' ink roller, lay on a sheet of paper aud apply pressure iu a screw pre^s.—T. \V. Boord.

(4787.1-SPEAKING TUBES.-Gutta percha is the best of all materials for this purpose.—Sjgma.

QUERIES. /

[4788.]-DISSOLVED EONES.-Xv-ill some correspondent inform me how to manufacture dissolved boucs, and other artificial manures, on a/small scale for use iu my garden ?—J. H. B.

[4789.1—MAP,—How can I niafko my paper map adhere to the linen, as I had the lñ/on absorbs the gum? Beriso.

[4790.]—COPYRIGHT.—ahn any reader kindly inform me how I am to proceed inr tho case of my wauting to enter anything at Stationers' Hall, or anv o'ther register of copyright? Whuove/will do so will oblige.—Mus.

[4791.]—HORIZONTAL OSCILLATING CYLINDEIÍ. —Cau any reader rcffSr me to a number of the English Mechanic oontaimalg a description of a horizontal oscillating cylinder? If it has not hitherto beeu described, will some- engineering friend kindly explain its mechanism, and assist an amateur trying to make uno?—F. A.B. Salt.

11792.]—PROBLEM.—Will " J. K. P.," or some brother reader kindly solve the following? (a) A force of 1001b. is resolved into two equal forces acting at an angle 6(1°; find magnitude of either component. An-. 57*7. (Í») A force of 1001b. is resolved into two equal forces acting at an an^le of 90', find mauuitudo of either component. Anj. 51'ï. Please draw ligures to illustrato both.— Onus.

[4793.]—IRON SHIP.—Would some of the correspondents of the Mechanic oblige mo with the method of laying down an iron ship (of any size) ?—T. H. Rooas, Sunderland.

Г4794.]— ELECTRICAL.-TO "SIGMA."—"Sigma" (to whom many thanks), says (No. 281, p. 481), that in cases requiring a largo current, аз for magnets, &o., the peroxide of manganese battory is "absolutely useless." On the other hand, he states (p. 482) that the sulphate of lend battery "yields n Ыща current," aud would therefore, I infor, be very suitable for magnet-. Will he kindly inform me whether a Hin. magnet with six convolutions of No. 18 B.W.G. covered wire would, with 8 pint cells of the last named battery, lift 8oz. 1-löin., the connections measuring about loft., or whether ho cau suggest any alteration in diameter of wire, uiunber of cells, Ac. Also if the battery should be coupled for quantity or intensity. Au answer ou these points would much oblige, aud probably save me needless expense.— W. J.

[1793.1— ENAMELLING SLATES—I shall feel truly obliged if one of your kind readers will bo so good as to e\plaiu to me the process of enamelling (or japanning) on slates; or iuform me of any book on the subject. —Do Me So.

[4796.]— UNIVERSAL SWIVEL GAS-JOINT.—Will D. Clark bo so kind as to iuform mo what kind of a joint a universal swivel gas-joint is? Also, what kind a telescope joint is.—Anon.

[4797.]—TUB HOOPING,—I have a great deal of tubhooping to do, and I want some one to tell me how to get the nroper level, as I cannot get them to lit proporly. —Anon.

[4798.]-STAINS ON WOOD.-Will some fellowreadcr kindly answer me tho following, bv giving the reason why some joinery work with which I am connected has. on being stained and varnished, becomo covered with black stains, in the form of spots spread indiscriminately over the isurface,' but especially over the panels ?—Geomktros.

[4799.]-SCIENCE AND ART DEPARTMENT.—Can any of our technical friends give any information concerning the Queon's medals for subjeci 1.; are students that have passed in honours eligible for medals ?— L. M. N.

[4800.]—GEOMETRY.—Divide a septagon into nine equal parts by lines parallel to one edge.—T. Störet.

[4801.]— GREENIIOUSE.-Will some brother subscriber kindly send me a sketch (if our editor will allow space for it> of a small greenhouse. I wautsome decorative work about it, such as gable boards and carved top; also, what would bo best to heat the same, as I cau have steam conducted to it with little trouble? I want tho houso span roof ¡»—black Country Joe.

[4802.]-WATER POWER WANTED.—Will some practical person advise a professional man with шеchanioal and.farming tendencies? I have two small farms which could be much benefited by irrigation. Each has a stream running aloug the lower boundary. The stream, though never dried up, is in summer so diminished that it probably might he convoyed through a 0in. or 8in. pipe, and then velocity-is also very small, the fall being perhaps 2ft. to 3ft. Î want a self-acting power to convey water, by pipe or otherwise, to the higher level of lOft.or 12ft., by means of a pump or other sufficient lifting arrangement. I have made a rude model on the principle of a screw within a tube, intended to be eausod to revolve by the pressure of water passing through the tube. The model tube is lüin. long, lin. bore; the screw lias but one thread, making a coil of thirty-nino v itbin the length. I am now aware that the pitch of the screw is not correct, aud that a second or more threads would give more power. Under water pressure of 3ft. or 4ft. шу model gives a rapid velocity, but шоараЫо of resisting even very slight obstruction.

[48Ü3.] — FAURE'S BATTERY.—I have recently purchased one of Fauri's batteries, and shall bo greatly obliged if some correspondent will inform me how it would answer to fill the carbon buttle with a saturated solution of bichromate of potash instead of nitric acid.

—D.CDALCS.

[48Ü1.]—THE LATE DROUGHT.—Being deeply interested in the progress of inoteorological science, I should like to learn whether tho late severe drought iu the British Isles and hi France has also prevailed iu remote regions, as in Russia, North America, or elsewhere. As it may have extended more or less over the whole northern hemisphere, I should esteem it a great favour if any brother reader, who may possess notes on the weather or the amouut of rainfall during one or more of the past three or four mouths, or any romarks on the season, from remote stations on the globe, would kindly and briefly inform me through the medium of your columns.—C. F.

14S0Ú.]—HEATING APPARATUS.—Will one of your readers kindly inform me the best way of constructing aud heating coil pipt* for tho warmth of a small office 6ft. long by 4ft. wide? I have in previous winters used the gas-jet, but find it affects my health, without comfort to tho feet. I have an idea that a boiler outsido the office in an enclosed passage, " now erected," might be heated by gas without being unhealthy, and causo the steam to pass through tho pipes near the floor to warm tuo place. Advice upon this, or any other method, will be received with thanks by—A Poor Clerk .

[4806.]— DISCOLOURED IVORY STATUETTES.— Can any of your numerous correspondents inform me how to restore the whiteness to ivory statuettes that have become yellow and discoloured ?—Wahsrof.

[4807.]—REFLECTOR STAND—Would auy of your readers, who has mounted silver or «lass redectors on stands, inform " a youth" how he could make a stand (equatorial preferred) for a speculum of about 6in. diameter? If any friend has got one ncarWigan I should be very glad to see it.—Amateur Astronomer.

[4808.]—THE TELESCOPE.—I am a beginner in astronomy and want a telescope. As I cannot buy "a good " refractor cheap, I thought I múíht make a good reflector for a far less number of pounds than is asked for a good achromatic. Suppose I had "about" three pounds that I would lay out to make a good useful telescope myself, which kind would be the best for one like ше to make if 1 bought the principal parts? In some bonks I find they ave dead against the reflector. And what size of object glass would be equal toa 6in speculum? If.lfr. Piirkiss,"F.K.A.S.," Mr. Proctor, or anv other reador could help me I should ho much obliged'. P.S. I have a small achromatic with »Ц object-glass with a power of 1ГД only.—Amateur Artronomer.

[4809.]—CELESTIAL GLOBE.-I have a celestial globe, lftjin. in diameter, made by Benjamin Maitnin, which getting rather old I had cleaned and varnished, but when I carao to use it the varnish peeled offin some places; could any of your readers tell me whether I can got it re-covered, or can I do anything with it myself, as tho paper has also come off .in mauy places. What would be about the cost?—Amateur Astronomer.

[1-tlO.]—LARD AND S.UiSAGES.-I shall be obliged to auy correspondent who will iuform me of a simile apparatus for rendering lard, one that will not require much attention, and without risk of burning: also the best way of pressing the "scraps." I should also be obliged to any one for я good sansaçe recipe, aud instructions how to make them,—Shoi-keefeb.

[4811,]-WEIGHT OF WIRE.—Will any electri/ril correspondent be kind enough to state how maav yard« of No. 35 copper wire make a pound; th¿ bare wir" cotton and «ilk covered?—Tomf.teb.

[1812.]—VERTICAL SLIDE REST.-Will "J. К-P." be so kind as to explain a vertical slide rest, as I require to fit one up in conjunction with a friend.—Tomris.

[4813.]-SMALL PLANING MACHINE.—Л few weeks ago I asked through your valuable journal how to fil ар a small planing machine, and several correspondents kindly answered me, but none gave me the information I desired—viz., how I could make the patterns and «t tho castings together myself? If one of them will be » kind will greatly oblige—Tometeb.

[4814 1-WATER SUPPLY.— Will some pr/tcUrJ plumber explain to mo through our invaluable piper the following? I am about laying a pipe from a. reservoir to our house, a distance of nearly 700 yards, at a rous4 calculation. The rise will bo 13ft. above the cistern, or ш other words, a pole 13ft. long standing in the clsurn the top of it would be on a level with the reservoir' Now I should like to know all that is required besid« the pipe. I have seen two taps in the side of s pipo in t similar situation. I want to know what nse they we« or if it would do without them. I understand it ы »¿.' solutely necessary to have a turn-off tap at the res«, voir, and is it likewiso necessarv that there shonld b> any air pipe; if so, in what part ¿f the pipe should itb»' The neighbour's one that I have examined often reí! slower and slower, nntilit stops altogether, ami by turaing on one of these taps that I mentioned as being at Ц* side of the fountain pipe, and allowing it to run a wide, perhaps seven or eight minutes, when I shut it ■ immediately runs faster into the cistern, and contins,! all right for a week or two, when tho same ha.« to be d» again. Surely there is something wrong. I may mc tiou there is no air pipe in it, and we are not eatisiri altogether with the plumber's reasons. He save the юг* is holed somewhere, but it is so recently put ' in I cannot think that is the cause. Perhaps at the same time you will let me know what the best thing is to staff а force-pump stuffing-box. Is leather, cut washer-shaDe. auy good ?—A. "^

[4815.]-GOOD REED ORGAN PIPE.-Wai anv fellow contributor inform me how to make a food reed organ pipe? Also tho size of pipes required for an Sxk stop, voiced ou "Adept's" fluie principle.^* CsttTkidutor.

[4-H6.]-CLEANING FURS.-CouU aar of your correspondents kindly iuform me how ermine and мМ<, furs are cleaued? lam living in the cuuutrv. and it would he a great accommodation to me if I could do them at home instead of sending them to London.—

[4817.]-STEAM CARRIAGES.-Can any brother reader nnform me whether there is imv law respecting

the use of steam carriages ou the turnpike-road, and what it is ?—R. J.

14818.]—RUBBER VALVE.—How long will vulcanized India-rubber valves stand in the condensing part of a low pressure steam-engine, usual heat? Aud how many degrees of heat will they stand without being destroyed supposing superheated steam were used, and having to' blow through to obtain a vacuum before starting'?—

[1819.]—SCIENCE QUESTION.—Will any kind readeiinfurrn me how to work the following question occurrim,' in tho Science Examination Paper for Honours o/last May? Determine the locus of the curve whose equation is (y —2)3 + \x—y/2}i = v^2-unit = lin.? Andnhiohis the best book for such study?—X. Y. Z.

[4820.1—EBOXISING.—Will some one bo kind enough, to describe the above process for tho benefit oí—Gahfax.

[4821.] -PENDULUM SPRING.—What is the usual method of determining and fixirg the isochronisin of a pendulum spring, in eitlicr English or foreign watches? I havo a watch (verge) with the top pivot brokeu. Will some of our competent bretliron kindly toll me tho easiest way to put iu a new pivot? I have also a watch with fusee arbor square completely off. Is it possiblo to put in a new square without taking the arbor completely out of the fusee? If so, how am I to do it? If not to ho done in that way, can tho arbor be taken out of the fusee and another fixed securely in its place? And how are they usually fastened in. I also wish to know if the pinions two aud three of watches have their leaves turned down to a shoulder with the common graver, and how, in tho turns, to form a seat for the fixing of the wheels before riveting on? Also what ought to be the relative size of the ferrule to file an ,cle turned? When you use the bow, how do tho faces of wheels in watche-s receive the smooth snrfaee they generally possess? Isj it turned up with the graver in the tnrns after the wheel is riveted on the pinion, or is it smoothed on the poliabing block? Are there no small lathes in use with flywheel and dead centres forturning up watch whools and pinions? Would they be equal to tho bow and fcrrmj for light work ?—Improver.

[4822.1— LEAD BURNING.-I wish to gather gome information respecting the art of lead hurniug. Л description of the apparatus required, aud all necessary particulars. Or is there a work to be obtained thutwill give tho necessary information ?—W. O.

[4H2S.1—STAINS OX STEEL.—I have hid some "1 my polished steel tools damaged by rust, after taking off the rust (by sandpaper und oil) a dark mark remain*. I shall bo glad if any of уоцг readers will inform me how to efface the dark uiari<,>nd restoro the original polisb. —Т. W. U.R. ... .

[1821.]—BATTERIES,—I quite agree with the remarks of Johu Legg (1. 316, p. 570) in his description of the sulphate of lead battery as regards its constancy, ss it is the best I have had to deal with, but ie not the form in which he describes it a patent? Will .lohn Le>rg describe the manganese battory and oblige :'—Koanoke.

[4825.]—ELLIPTICAL CUTTING FRAME.—Csn any of your correspondents tell me how to make an elliptioa1 cutting frame for omainenLil turning? I know there lias not beeu anything of the kind drs<-ribod lately, as I have taken in tho Mechanic for some time. Please give full and complete directions aslata lotallv unacquainted with this tool. It is for a 4in. lathe.—J. ÍV. li.

[4826.]—SCREW CUTTING.— Having a great many screwfi to make I should be gl *'t tohoar your corrc*poudenia' dodges for getting them done quickly. The

screws arc bra-s and all the same size, willi the bends milled so as to turn theui v.ith tho fingers; shout $in. long, ?in. diameter <>f liead, £ screw. I got them cast in lengths of 13.—J. W. O.

[■4827 ]—MOTIVE POWER FOR LATHE.—I am in wantof a motive power to drive my two lathes, grimdstone drilling machine, &c, &c. Can any one inform me nf aciieappUn to drive them (one at a time) as I find treading them very hard work from morning till night? -^J. W. G.

r4S28.]-SPECULA'GRINDING.—TO MR. PURKISS.

Will #r. Purkiss kindly answer the following questions

for me t What Bhoold be the diameter and thickness of the trass tools for grinding a perfect spherical curve on a class disc 4in. diameter? What are the different finenesses of emerv used, and how long ought I to work each kind? How can I tell when the glass is ground fine enough for polishing? Ought the pressure to be light or heavy when using Lho finest ornery? When the tool is covered with a piece of linen rag, and putty-powder is used, how long ought it to take to polish the glass? Should I press very heavy in polishing? Is it necessary to wa*h tho putty powder as purchased in the shops.— Aplanatic.

[4829.]—TO "INDUCTORIUM."—Will you be so kind as to inform me in what respect is cotton covered fine wire inferior to silk covered wire for induction coils, when both aro varnished with shellac or paraffine ?— Fi>-e Wjre.

[4830.]— DIAMOND POINTS IN DRILLS.—Will some brother reader tell me how to fix tho diamond points in drills? I am told they are soft-soldered in; I have tried it aud failed. I could not make the solder take to tho diamond.—R. N.

[4831.]—FORCING AIR CURRENT.—I want to force n continuous current of air into a chamber not less than 180c of heat. Any information on the above subject will greatly oblige.—An Anxious Inquibcr.

(4832.]—PAINTING METAL BATH, TIN, Etc.—Can you, or a brother reader, tell me the best way to paint a hip-bath, so that the paint will not come off very readily with tho water? Sad.. What la the process of stoving tin poods? 3rd. What paint is best for tho purpose ?— X. Y. Z.

[4833.1— RENDERING CALICO AIR-TIGHT AND WATEU-TIGIIT.— Could any of your correspondents tell me the best way of rendering calico air-tight and water-tight ?—Yeloc Cirkdekf,

[4834.]—LINK MOTION.—Would Mr. BaBkerville or any other please give a simple rule, showing how to draw in the excentric pulleys for an indirect acting link? —P. B. Mc G.

[4835.]— INDIA-RUBBER.—I find that india-rubber niter it has heon exposed to the light two or three years loses its toughness. Iu fact it becomes brittle And useloss. Can any one suggest a mode of preserving the material?—J. P.

[4836.]—ARTISTS'LAY-FIGURES.—Can you or any brother reader iuform me how thejointr*. of the patent papior-nii'icliL mannikin or lay-figure used bv artists are put together? Alsa the best and cheapest method of making a papier-mache suitable for tho purpose, and how are they moulded from life ?—G. S. Walbden.

[4837.] — FOREIGN WOODS. —Being desirous of obtaiuing information concerning many foreign woods which are available for the uses of the ship-builder, carpenter, and cabinet-maker, I should be much obliged if my fellow readers could direct me where I can find printed descriptions of the properties of any or all the following woods— some of which were in the International Exhibition,—or any other woods especially suited for rnbinet work, with which they may be acquainted, or by their assisting me in my endeavours to acquire knowledge by describing their properties in the pages of the English Mechanic, should you, Mr. Editor, think the subject, which is really an important one, worth the space. Blue mahogany of Jamaica, bay, beet, boef, bergamot pear, camphor, canary, cocus, lilac, iron woods (very variousi, purple wood,red ganders, sandaL sassafras, satin, sabicu, zebra. American woods : Elm, black oak, white wood, mangrove of Trinidad. African wood*: Oak, mahogany, green ebony. Australian woods; Blue gum, cedars, mahogany, red wood, iron bark, stringy bark.— Lignum Vita:.

[4838.] -PEDESTRIAN TOURS.-WiU « Scholastics » or any other of your readers give me some suggestions as to the best direction iu which to walk under the following circumstances:—A friend and mvself intend making a flvo days' tour at the close, of tho present month; mv faend takes coosiderable interest in architecture, especially that of the cathedral tvpe, while I on the other hand tako more pleasure in the attractions of scenery. We wish to helect a walk (of not more than 25 miles a day) which will givo satisfaction to the tastes of both, without making more than a very limitod use of the railway or other means of conveyance. London is to be our starting-point. "Scholasticus" has kindlv offered information as to "good and cheap houses for -sleeping, &c.t" and I think any such hints would be of great service.—F. P. P.

L4839.]— CANNON.—How can I alter a muzzle-loarlin-,' nwEia, ?. ft hreech-lo*der? Will soma kind reader oblige?—Gunner.

HlK:1-r«UNP0W?ER--In Mangnall's" Questions on 5, r?ri, bt,,'fed th'1^ ff^Pttwdcr was invented by one t« nn'4^1;IU IhftV0 alw"-vs understood that it bW £? «',? U?ed m Chiim ai»d other eastern countries anga, ^t v!lt'ftJe- iU M,l^aaU (who is considered nS.nrti ♦■ y)iSU.tea thi* witL an>' reservation or qualification I shall be glad ii „uy of your learned readers can throw any light on this subject.-STUD^r. TMLSliJ —SPONGES—c*o any one tell me how to andflS S*tT*Z J Qse 0ne ^ in A sponge bafh" D Nte * yeRra timo tt iaU* *° Pieces.

divide ^IX^??111^ l flud U Bomewhit dimcultto who will be a)ln t T ".*! 8omo rea,lerB °' thi3 J°*"»l ifb«*«.- Ii? ° solve ihii Problem for me. I give an illustration of the piece of land. B BW1

AB =1033links, A C =* 244, C C = 630, and B D =

[graphic]

840 links. The diagonal line from B to C = 1138 links; the perpendiculars D x 482, A/210.

N.B.—Each person's share of tho land to fall perpendicularly upon the aide A B, and also the number of links in length for each person upon the given line AB.—An Amateur Land Sukvkyou.

[4813.]—MUSICAL. — Wrould some correspondent kindly tell mo where I can procure an old song on tobacco, eaoh verse ending with the refrain "Think of this when you smoke tobacco "?—D. N. E.

[4844.]—NUMISMATICAL.—Will our good friends Mr. Henfrey or Mr. Batty give us some information as to tho best practical method of displaying coins in a museum, taking into consideration safety, expense, and educational use, the best mode of affixing names, dates, &c.? If they, or any of ourjnuinisniaticsl friends will do so they will much oblige—Samuel Smith.

[4845.]—ELECTROLYSIS.—I have repeatedly tried to effect the decomposition of water by using six linnpen'scellis. quart size, and a common ** shucking coil," but have failed. Will " Sigma " be good enough to put me right?—Wobk.

[4846.]— LOGARITHMS. —Will any brother reader kindlv solve the following in full ?— Given log 7*5014 = -8751423, log. 7'5015 = -8751481, find the number correspouding to logarithm 3*8751461*. Ans. -007501467.— Work.

[4847.]—NATURAL FORCES.—TO •• SIGMA."—! desire to thank '* Sigma" for his ready, kind,and complete answer to rny letter, and if I do not trespass too much on his time I should feel obliged if he would indicate a book or books which show or treat of the relations of the forces of nature. I have only studied electricity for a couple of years, and of course am not quite so clear on the subject as I should like to bo; however, I cannot help thinking that it is intimately connected with heat, and am very anxious to read a good authority on the subject. I nave read a great number of smaller books; but none of them seem to generalize. I should also feel greatly obliged if '* Sigma," or any other reader, could give me a tolerable description of the machine which Professor Jacobi (in 1834) constructed to propel a boat on the Neva.—Thinker.

[4848].—HYDRAULIC APPARATUS. — Can you or any of your correspondents inform me what the probable cost would be <>f furnishing and fixing, ready for use, a hydraulic apparatus of, say, half a horse-power; and secondly, what would bo the approximate cost per diem for working this power, the water being supplied by meter. The above is required for working a small printing machine.—Sunderland.

[4819.J—MEDICAL.—Would any brother reader give a simple test to find whether medicine in a liquid or other form contains mercury ?—Patient.

[4850.]—THE TELESCOPE.—I wish to thank Mr. Purkiss for his very kind and complete reply to me with respect to the size of the flat. Mr. Purkiss has in. his letter supplied valuable and plain information that will be useful to many of our readers, and which has never been so supplied before. I had bofore writing to him adopted a fifth, but I believe a sixth is generally used. I had a wish to know hi* own plan, but as he justly observes, a fifth or fourth gives a little play. I now wish to draw his kind attention to another matter. I have tested a lOin. mirror oi my own make with his bar test. I used a power as high as 640, which tho mirror stood perfectly well, both before silvering and after, and on the brightest stars, and yet I cannot get a good definition. I have tried the test over and over again, and with good air (for I had my refractor out the same time) and each night trying it on tho stars and Saturn, and it will not give a star disc nor show the division of the planet's ring. I invite Mr. Purkiss' opinion as to whether a bad flat would not allow a good mirror to show the test-bar straight and parallel, and what effect imperfect centering would have? There was one thing I particularly noticed, the edges of the bar was not seeu sharp and well defined like a sharp and distinct shadow, it looked like the shadow of an object (say a penholder) when held nearer to a lamp than to the white blind on which I projected its shadow, I expected to see the shadow of the test-bar sharp and d-iitiuet us when the penholder (is held near to tho white blind. When I looked tit Jupiter, there seemed to be a round shadow of the planet on one side; this shadow was not seen only when the planet was alittlo out of focus (insido the focus). I have sometimes seen the same appearance with the stars. Now this would seem to prove that my mounting was not good, and that the mirror gave a double image, which from the pains I took in mounting the mirror 1 am not willin ; to admit. The flat I have used is only a piece of ordinary plate glass. n>t wUet pieces. How d.-es Mr. Purkis-t succeod in silvering alter failing a few time-? First, I was induced to depart a little from Browning's directions, and have always si.ice succeeded iu getting excellent films, but they are always slightly transparent. I think this should not be the case as there must be some loss of light. Would it not he advisable to strensjthen the silver solution a little, and so get thicker Alms? Lastly, can Mr. Purkiss, or any other of our able correspondents, tell me whether a truly parabolic,d mirror will converge rays to one identical focal point from objects at any distance, as well from an object at 50 or 00 Yards, as from the stars ?—G. C.

[4831.]— AEROSTATICS.-To what space a quart or gallon of coin.u!>u air can be compressed, and what expaudiug power that would be? Also whether there is any gas igaset>j or fluid more compressible, and with a greater expanding power ?—J. R. L.

[4852.]—GOLD CRUSHING.—Copper plate being used iu connection with our gold-crushing machine*, the copper ii coated with quick-diver to retain the gold as it flows over the same with the water and crushed material. After several months' use the plates become

impregnated with tho gold and silver. A certain experiment is used to clean the plates. The plates are painted with a Bolution which is black, and exposed to a certain heat, after which the gold comes off in a thin shale. What is the solution and proper mode of operation to effect the same ?—J. Russell.

[48030 — GEARING FOR BUCKET.—I shall be thankful for a simple rule for striking a pattern or gearing for a bucket, such as used iu a drawing lift (or ;iumpl, say for a 9in. or Gin. working barrel.—J. Russell.

[4854.]—SWIMMING PADDLE.—Some time ago I constructed a swimming paddle, which for some reason or other docs not answer the expectations I formed of it. My original intention was to work it entirely under water, and I thought to avoid tho drag of reflex action by placing the blades at right angles to each other, and feathering at each stroke. I soon found this plan would not answer, .since it necessitated a change in the position of tho hands, which weakened the pull. On the next trial the blades wero made to correspond in position, being lifted out of tho water alternately, but even then candour compels me to admit that it is quite as much a hindrance as a help. Will auy reader kindly tell me what they think to be the cause of failure, or whether in their opinion longer practice with the paddle might render it really serviceable as a means of progression in the water?—Percy Johnstone.

[48550—BATTERY CONNECTIONS.—Iliave twentyfour Grove's batteries, and am puzzled as to making the connections. I have tried slips of copper, bent tight on to the platinum, but this tears and wastes it. I do not wish to incur the expense of purchasing binding screw*, and unfortunately I had the platinum cut too short ti> allow of its being bent over against the next zinc. If any brother reader could inform me of some simple method I should bo greatly obliged.—R. T. Bell.

[48560— WENHAM'S PARABOLICAL REFLECTOR. —Would Mr. Pocklington nay if Wenham's "paraboloid reflector " can be used with low as well as with hi^h powers? The idea mentioned by your correspondent "A. A. F." of organizing an " English Mechanic Microscopical Society "is, I should think, a good one, and will, I do not doubt, bo acceptable to many of your subscribers.—A. L. B.

[4857.1—MODEL WINDMILL.—"John James" {see 4605) will oblige if he will say where his model windmill can be seen, or givo a sketch in your paper; also cost for a boat 25ft. long and 5ft, Bin. beam —Inquirer.

[48580—THAUMATROPE.—Will some one tell me how to make a thauinatrope ?—J. M.

[48590—LOCOMOTIVE DRIVING.—What ii the causo of a train progressing by a series of jerks? Is it due to bad driving or bad management of the firing '.'— Steam Rider.

[4860.]— REGULATION OF COMPASS.—Will any one tell me how the compass is tested and regulated in iron ships? Is it absolutely necessary to put tho ship with her head to the north ?—Nautis.

[4861.]—INCLINE.—What degree of inclination would stop a locomotive drawing four times its own weight ?— 8. B.

[4862.J—LEAD POISONING. — Can any of your readers furnish me with an antidote against white sugar of lead poisoning ?—W. E.

[48080—GLASS ANALYSIS.—I shall feel obliged if Mr. G. E. Davis will give me plain directions for analyzing glass.—J. M.

[48640—MANGANESE BATTERY FOR IGNITION OF POWDER.—Will " Sigma" or Mr. Jarman kindly inform me whether they consider that six quart-cells of this batterv would suffice for tho purpose of igniting gunpowder? In that case would a piece of platinum wire passing through tho powder effect the explosion, when the circuit was closod? I also wish to know whether constantly shifting batteries about, taking out of their boxes, &c, iu anv way etfacts their electrical condition ?—C. H. B.

[48650—LACQUERING BRASS WORK.—Canyou tel me how to lacquer small brass work so as to improve and brighten the metal? I find tho lacquer dulls and spoil* the work, rather than do it good. I made tho metal warm and applied the solution with a camel-hair brush, but the surface comos ont so dull that I must bu wront,' somewhere. lunedwhatis called best gold lacqwer; if this be the right stud*, please tell me hoty t>est to use it? —Stick -in -thi -mud.

[4866.]—WATERPROOFING TIMBER ROOFS.—I should feel obliged if any of your readers can inform me how to render a wood roof of shed 40ft. long water proof. I have tried tar and sand, and after bngs nailed on and tarred. I want something cheaper than felt.— H. Seymour.

[43070 — AUSTRALIAN NUGGET. — Being the possessor of a sruall nugget sont to me by a verv dear friend in Australia, with the request that "i would* have a hoop mni'e of it and wear it tor his sake, aud being anxious that the hoop should be mude from that particular piece of gold (without the slightest doubtj I wish, if possible to make it myself. My object in troubling you is to inquire if any of the readers of voui invaluable paper will oblige me with ade.scription of the process required to accomplish tho object I have iu view.—A NitW Subscsiheu.

[48iK]- TRUMPET STOP.-Will any harmonium correspondent kindly inform ine whether n trumpet stop (worthy of the name) has yet been introduced on the harmonium; and if so, bv whom, or on what maker's instruments to be found?—Raka Atis.

[4869.]—LENGTH OF PENDULUM.—I have the movements of a clock, the escape wheel of which ha* 45 teeth, and it revolves once por minute, making iu that time (H) beats, each beat, therefore, according to my calculation, being two-thirds of a second; uow I wish to know what length the pendulum should be? I purpose making the hob of a brass cylinder, about 2in. in diameter and 4Ln. long, filled with lead, and the rod of seasoned deal, well varnished. I understand that "the ti.ne ot vibration oi a pendui'im varies as the square root of its length," but not being up iu mathematics I caunotfind the length for myself, and will thank anv of my fellow readers for the information.—Electko-maoNet, No. 1.

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ANSWERS TO C0REESP0NDENTS.

%* All communi cation a ehould be addressed to the Editor of the English Mechanic, 31, Tavistockstreet, Co vent Garden, W.C.

SOMNAMBULISM.—Two instances are recorded in Le* Mondes oí somnambulism being perfectly cured by the administration of bromide of potassium. In one case, a woman of the age of twenty-four who had bceu Hubjcct to attacks two or three times a week for ten years, was operated upon; the dose given was two gramme« of the bromide in seventy-five of water per diem, gradually increased to six grammes; the attacks became at once less and lees frequent, and entirely ceased at the end of two months. In the other case, а girl of eight was the subject; one gramme was given morning and evening, and the cure was complete and immediate.

A CAUTION.—R. Bennett says: "In the English Mechanic of the 26th A ngust last, page 546, under the head " A Valuable Table," arc given certain dimensions of boxes, which it is stated will contain the several measures or quantities there mentioned. These dimensions are in every case erroneous. The statement is not true, even on the principle that "you can put a pea into a bushel," since there are errors of defect as well as of excess in the table. Subscribers will do well, therefore, to put a note of warning against reliance upon it in the margin of their copies. I give an instance of error. A pint really contains 84*659 cubic inches, plus a very small quantity which may be disregarded. The table states that a box of 4 x 4 x 4| ( = 68), cubic inches will contain a pint. So it will, and nearly another pint ; but that is not, I presume, what the author of the table intended. In any view, the table is calculated to mislead and hence I am induced thus to address you."

[We obtained the above mentioned paragraph from a journal culled the American Artiaan. As it appeared to contain what is simply a matter of calculation, it did not undergo the customary editorial criticism. In future we shall hesitate before we insert any " valuable " tables found in our Transatlantic contemporaries.—Ed.]

COMPOSITION OF CHINESE L AC QUE R- WORK.— According to Dr. Wiederhold, genuine Chinese lacquerwork is done over tin-foil, and consists of a mixture of two parte of copal and one of shellac, molten together. When fluid, there are added two parts of boiled linseed oil; and, after the vessel containing this mixture has been taken from the fire, there are gradually added ten parts of oil of turpentine. If colour is required, gummigutta, dissolved in oil of turpentine, yields yellow, and dragon's blood, dissolved in the same liquid, yields red.

IODINE FROM CHILI SALTPETRE.—Professor Wagner says that the manufacture of iodine from Chili saltpetre already amounts to 80,0001b. per annum. The method invented by Thiercelin for its reclamation from the crude material is as follows: The mother liquors resulting from the manufacture of saltpetre arc treated with a mixture of sulphurous acid and sulphite of soda, in proper proportion, and tho iodine will be precipitated us a black powder. Tho precipitated iodine is put into earthen jars on the bottom of which are layers of quart/, sand, fine at the top, and coarse at the bottom : from this it is removedjby earthen spoons into boxes lined with gypsum, and a greater part of tho water thus removed. It ie яогаейглрч sohl in this impure state, or further purified by sublimation.

A CHEAP BATTERY.—Dr. Golding Bird describes a cheap form of battery with which an energetic current can bo evolved, sufficient to decompose water, ignite wire, charcoal points, &c. Procure the bowls of six tobacco pipes, and Btop up with sealing-wax the hiles left by breaking off tho stems; next get six email toy tumblers about an inch in height; place in each a cylinder of amalgamated zinc, put a pipe-bowl in each cylinder, and in the pipe-bowl a thin slip of platinum mil half-an-inch wide, connected to the zinc of the next cell by a platinum wire; fill the pipe-bowls with nitric acid, the tumblers with dilute sulphuric acid, and the battery is complete. When platinum cannot be obtained copper will work.

The following are the initials, 4c., of letters to hand up to Taesday morning, September 6, and unacknowledged, elsewhere :—

W. and T. P., R. F., R. R., J. H., P. C. V., J. O'Connel!, Edward B. Fenuesey, H. Pocklington, J. R. Alleu, Ed. James, T. W. В., Rev. E. Kermm, James Williamson, T. C, W. Kinmiis, J. B. Primas, H. P., A Young Man, George, Welby, U., Unit, Argent Sable, J. J. В., F. В. White, Zeta, Espérance, Alpha, Scraper, S. Dixon, G., A Student, Totnesian, Deri Errac, Cuthbert, T. В , A New Subscriber, A. S. C, G. W. A., F. J. Walker, R. N., Harry G. Newton, A. E., E. W. A., M. W. G., Paterfamilias, Ivory, Vulpécula, H. P., G. Valentine, Cabinet Maker, С. H.Wvnn, Mechanician, T. L. H., J. A. M., Augustine, Thos. Fletcher, Argus, Farmer, A Mere Novice, A Runaway, Z., G. J. W., T. A., A. Childs, Scio, Idea Cather, W. Pocklinton, H. H., H. W. Henfrey, J. A. H., J. Andrews, Student, Rupert, John Hewitt, G. L., H, W. Reveler, R. D., A Morayshire Man, Mr. Batty, Epps, A. P., W. E. D., G. Prew, J. E. Y., E. Cooper, Atomic, Chemicus, Quill Pen, R. A. M., T. M. Simkiss, North Pole, Graham, F. S. H., Sigma, J. K. P.

Henry W. Hentrey, of Brighton, says :—" I think that with such improved printing, engraving, and paper, the English Mechanic ought soon to double its circulation."

The Phantom Wheel.—Additional letters confirming the views of preceding correspondents, from "Bicycleist," James Thompson, and "J. R." They all repeat the same story, that the "Harmonious Blacksmith" spoke from insufficient experience.

W. S. Owen.—Advertisements for Sale Column must be prepaid.

Mb. Browmidge.—We don't answer queries through the post.

T. H. Soîierville.—Next week.

T. O'connor.—All received from you haa been inserted.

J. H. N.—Thanks. We have had tMo many «irte* of articles of late, and cannot promise to insert yours at present.

T. W. Boord thanks "Urban" for pointing out the uiiatake in his answer to" Young Photo." qy. 4622. He "carelessly mistook the solution he nitnuoned fcr an old photograph bath '' and gave details accordingly.

F. Darkin.—See Mr. Tydemau's letter, 301, p. 467, and the note thereto. Ail correspondents tell the same tale.

Canadian.—Such a letter should be stamped with some authority.

G. Firth.—With every disposition to gire the widest latitude to correspondents, we really do not see the practical use of writing or inserting letters which are inoro as a pedantic criticism thar affording solid information to our readers. Let '*ti. F." imitate "F. R. A. S." and Mr. Proctor, in sending us substantial contributions, and we will insert all ho scuds. He evidently possesses great ability, and his last letter is not inserted because we have no desire to encourage corresr-imdenco spiced with provocative innen dos.

Tau Tau.—Dr. Grindrod'g " Hints to Dyspeptics" was published many years since and may now be out of print. The Doctor was uncourteous in not answering your letter, and particularly when you wanted to buy his book. Perhaps this hint may meet his eye.

R. Baldwin.—No stamps enclosed.

C. A.—Krankentrager means " bearer of the sick," as a porter attached to an ambulance.

Е. Smith.—Copper melts at 1996 Fabr.; brass, at 3807- Fah. ; tin melts at a lower heat than lead.

Egrec,—The value of a t baler, either in Prussia proper or Germany, is 3s. English money. It is divided into SO silborgroechen.

A Suggestion.—"Bcriro'' suggests that the English Mechanic And Mirror Ok Science should be called *• The Amateur Philosopher." The reasons given arc that in inducing others to become subscribers it was supposed the English Mechanic was tilled with descriptions of machinery and such like, and that "the highly intellectual class " will not take in a paper supposed tobe produced for mechanics. There is nodoubt much in what "Beriro" says. But it is not an easy thing to alter the наше of a paper. Neither do we think we should improve matters much if we called it "The Amateur Philosopher." The English Mechanic is to all intents and purjioses a scientific journal, and we have often regretted tl.at a more generic name was not given to it at the commencement.

Aviarían.—The chough, or mountain crow, is seen in considerable numbers in Scotlaud, Wales, and in Cornwall. It is found in abundance on mos t of the mountains of Europe, and particularly in Spain. Tho scientific паше is Fi'ty'tlti* ¡/racu'.us. It is known by its long arched beak, which, with its short-toed toot, is a brilliant scarlet colour. The eyes are dirk brown, and the plumage glossy black. It "is about loin, long by 31iu. across the expanded wings.

J. Т. B.—The Marquis of Worcester's perpetual-motion wheel was exhibited in the Tower about 36*8.

Т. H. Rogan.—Any queries on tho subject you mention, should appear.

A Young Beginner.—Simply limejuice and glycerine;

Pressure.—Write to Jabez Francis, Roch ford, Essex, or Fairbairu & Co., East-passage, Long-lane, Suiitnfield, London.

Francis Nash.—No.

Un Jeune Belge.—Mo-it of the numbers in Vols. VII. and XI. are to be had.

The " Sixpenny Sale Column" is the only place in which can appear queries by B. W. J. Williams,

C.B. T.—See back numbers.

Oliver Cromwell.—Much i information on gilding is to be found in back volume, especially numbers for September 24 and October 1 and 8, 1869.

Pompey,—Write the publisher.

J. W. Green.—A moment's consideration must conrince you that we cannot be responsible for recipes and other directions given by our correspondents. If

yon want us to look further into the matter you mast refer us to the number of the reply. W. Whetter.—No stamps sent with exchange. Inquire at the Architectural Association, 9, Conduit-etr«*, Regent-street. J. David«.—Such a discussion has taken pince, and the

majority appeared to think electricity beneficial Tometer.—We hare not received them. John T. Neelron (Windsor, N.S.W.).—The sub scriptum,

with extra postage, is 17s. 4d. per annum. R. B. Scott,—See back numbers for information respecting construction of aquarium. A. H.—A sheet of copper 1ft. square by l-16in. thiek

weighs 2Hlb.; the same in zinc, 2Slb. T. Smith,—Patents are granted in the United States for

seventeen years, and cost £21 10s. J. B. Ï).—No. A Prussian mile contains 24,712*5 En-dL-b feet. The Swedish is the longest, containing 35,£€гЗ English feet. Inquirer.—No. According to the Chartered Gas Con> pany, some specimens of Boghead Cannel coal produce 15,000 cubic feet of gag per ton, with an illuminating power of 87*75; while Dr. Fyfe, with other kinds of Boghead, has obtained 15,486 cubic feet, and an illuminating power of 53*0. Newcastle coal averages about 11,000 cubic feet, giving a light equal to thirteen candles. W. R. Bi Rt writes: *' WTill * Foreigner ' kindly communicate with me at Cynthia Villa, Walthamstow, in order that I may append his name to the lunar catalogue as the authority for the intersection of the fissures webt of Fonteuclle, discovered by him on the 20th of July. 1870?" G. B.had better consult "Chats on the Constellât ions" Id

English Mechanic. R. T.—Your query is incomplete, write again. William Stevens.—There is no such book. The nearest approach to such a work is made by the *' Repliée and Queries " contained in the pages of this journal. Sabar,—Write to any London toy-maker. For secoDd

query sec back Nos. A Very Old Subscriber.—Without more particulars it is impossible to identify the figures engraved on your seal. T.welsh.—Any polishing material with a little exertion will brighten tin dish-covers. Possibly the tin iworn off, in which case the covers will need re-tinning. Bernardin has sent a similar replyto query 4511. Weight

of brills, ns W. Moor, jun., last w'eek. S. J. Northington.—Consult a reliable man who has

capital, and who understands such things. F. F. Henbert.—Too theoretical for the space thefeifer

would occupy. Why not ask a query? Rev. E. Kern An in a private letter ьаус—" 1 must congratulate you on the unmistakable rewA-so -jou have so fearlessly announced of cutting off discourteous letters. I have every confidence that the effect will bo just what you say in your note on the letter of 'Lex.'" H. W. J.—Send your address.

A. L. T.—There are 225 sheets in a box of 1 С tinned plates, each sheet measuring 13$ x lOin. ¡ the weight is 1 cwt. Brush.—No. Schwoinfurth green is a more beautiful and velvety pigment than Scheele's green. Equal parts of a boiling concentrated solution of acetate of copper, and of arsenious acid are mixed, and when the resulting olive-creen precipitate is boiled in the liquor from which it was precipitated, a new deposit takes place in the form of a flense granular green powder. It is also readily made by adding to the boiliug solutions, their own weight oi cold wafer, when, in the course of two or three days, crystals of Scbvrcinîurth green are formed. Foretelling Events.—" W. B." draws our attention to a prophecy of Zadkiel in relation to Louis Napoleon. The following is the paraded prophecy:— "But let him not dream of lasting honour, power, or prosperity. He shall found no dynasty, he »ball wear no durable crown, bat, in the midst oi deeds of blood and slaughter, with affrighted Europe trembling beneath the weight of his daring martial hosts, he descends beneath the heavy hand of fate." To profess to tell a man's future by the light of the stars in such vague language ae this, without fixing a time for The event of his Life, is, to our minds, pure charlatanism. This prophecy, as it was called, appeared in 1853 or immediately after the coup d'etat. Nothing could be easier than to intimate in loose Language that the man whose imperial career began in violence and blood would end some time or another in a similar fashion. This miserable prophecy is now being paraded as an advertisement. But tho impostor does not state a word about the prediction relating to the Emperor which appeared ш his Almanac this year. "The year 1870," he says, *' opens favourably for the imperial native. In March he finds much to occupy him with the matters of State. In June he is troubled by thp press, and he will be Likely to meet with quarreM and be rather sufferiug in the head and brain. Ш August he increases his armies and will be Ш ot warlike dispositions, and if at war he will gain semebattlc. About the middle of October he will have many sudden changes favourable to his wishes*, bul. about the 23rd day let him beware of hurts and accident. This vear is prosperous to bfm generally.*' Zadkiel says that this year will be generally prosperous to the Emperor, when^it has hitherto been the most disastrous year of his life. Wo have only pity for the deluded purchasers and readers of such a miserable publication. E. Muohey.—1, Lausdowne-tcrrace, Wandsworth. T. J. C—We have nothing whatever to do with tho prizes oueied by the now absorbed journal. Wo expressed our opinion about them at the time. It is also, we think, useless to apply to any one else, as the proprietor of the British and Foreign Mechanic was obliged to pass through the bankruptcy court, f A Clergyman writes us a touching letter in reference to hi-* reply to "F. F. 0." He says, " My letter, a>2, was no sooner beyond my reach than I wished it where it ought to have been-behind шо îire. However, I still hoped the yawning waste-basket—the dreaded enemy of so many—might get to be nnc- ч friend." He therefore asks pardon of fc\ F. C. (see " Answers to С r.*espondeuts,"r- O00),for any !i...»u yr u^wum. marks he шаг ha-, с written. A Clergyman says; "li we cannot write something useful, encouraging, and kind, it were far better not to write at all."

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