then varies between a 13th and 83rd in different qualities of iron, its general fluid specific gravity, and the diameters of melted spheres thereof, weighing exactly 18lb. or 201b., must be very uncertain. I would advise the querist to make the smaller model 54in. diameter; correct this by trial if accuracy in weight is necessary; and when corrected, add a 28th of itself for the diameter of the other. The smaller the ratio of two quantities a and b, the nearer will their cube-roots approach the ratio of 2a+bto 2b+a; so that to make the weights as 9 to 10, the diameters must be as 28 to 29 very nearly.-E. L. G. [4431.]-MENDING EBONITE BATH (Unnoticed Query). It is impossible to mend an ebonite bath, as the material cannot be melted or softened to cause it to [4438.]-COTTON SPINNING (Unnoticed Query).Doffer and Carding roller, 7 per min., Taker-in 350 per adhere.-SAUL RYMEA. min.-SAX. [4447.]-BOGIE ENGINES(UnnoticedQuery).-These engines are used on the North London Railway for their facility in traversing curves, which are numerous on that line. I do not know that they sare anything, but the weight is equalized better, and I suppose as they travel round a curve easier there is not so much wear and tear by the wheels grinding against the rails. One of those in use on the Nort's London was illustrated in No. 243, Vol. X.-SAUL RYMEA. [4463.] ROTATORY MOTION (Unneticed Query).I cannot imagine what mode of producing motion "Young Engineer" can have regarded as applicable to a heated fluid, and not a cold one. If he would explain this, the query would doubtless become intelligible. -E. L. G. [4471.]-INSULATING VARNISH (Unnoticed Query). The practice of electricians seems to indicate that no mere varnish has been found to answer, as they would not, in that case, go to the trouble of covering wires with silk, paper, &c. "Insulator" may be sure his attempts have been often made before so cheap an expedient was abandoned.-E. L. G. [4174.]-HORSE POWER.-I beg to thank "G. W. A." for drawing my attention to the omission in my reply to "R. W." (p. 5-18), which I did not discover until my letter was beyond recall. I ought to have said that the rule, as given, only applied to cylinders whose stroke was double their diameter. From this, of course, the power of any other stroke may be easily calculated by simple proportion. So that a 6in. cylinder, whose stroke is 12in., gives at 401b, pressure, a power of four horses; if the stroke be only 9in, the result will be thus:-12: 9:: 4:3 horse-power required.-VERTUMNUS. Surely this case need not be repeated for every angle, nor 1 sin a 1 cos a commonly used for dividing-compasses. With these at A. B. C. Diagonal: side: : 2 cosine a: radius From the log. of 100 x radius = 19 And log. cosine a (say 67 ) Or, if a be 150 ("Onus ") = 301030 11-698970 = 2-116130 Log. 180-08 9'937531 1-761439 Log 57.78 9-894944 1-714026 Log. 51-76 -E. L. G. [4640.]-FRENCH LANGUAGE.-" Patty's" question cannot be rightly answered without knowing whether he wishes to study French for colloquial purposes, or to enjoy its classical and other literature. A man may make himself able to translate Corneille, Racine, &c., and not be able to speak a word. For instance, I happen to know that Lord Lytton, long after translating Schiller, was unable to speak a word of German. He had in fact worked hard putting German into English, but had never put English into German. If " Patty" wants to speak, let him get " Ollendorf." If he wants to read and translate, let him procure "Levizac" or "Wanostrocht," and a dictionary, and work away in the old style till he is sick of it.-C. DEVANT. [4504.]-ELLIPSES AND OVALS.-If "J. K. P." would take the trouble (p. 618) to clear his equation of the, he would find it a biquadratic one, and the oval therefore a line of the fourth order. When he can find one "no more complex than a conic section," that is, admitting of deducing the from the y, or y from r, with only one extraction of a square root-without being a conic section, he will certainly revolutionize all mathematics as much as the Liverpool Euclid-smasher (p. 606) or "G. H.," the new quadrator of p. 612. That the curve, when the rod exceeds three or four times the crank's length, approaches an ellipse nearer than one would Nicholson's "Architectural Dictionary," 1819, under the suppose without trial, has been long known. In Peter word Oval, it is lengthily but confusedly treated, along with other ovals of the fourth and sixth orders that yield beautiful "eggoids," to adopt his barbarous term and of this connecting-rod oval and the oscillating [4492.]-RAISING WATER (Unnoticed Query).-TheIt is now above 25 years since the author discovered piston rod oval (as they would now be called) he says, easiest mode of reversing the motion is probably by the two above curves, and a machine for describing the three bevel-toothed wheels placed as in Fig. 303, page former has since been exhibited for sale in Cornhill, 584 (Sept. 9), but with C and D both fixed on one hollow which Mr. J. B. Taylor has applied to the art of axis that slides along A A, and at such a distance apart that only one at a time can engage in the teeth of B. engraving with considerable success; and though not in the same time, the quotient will be the pitch of the By shifting them along A, so that each may alternately engage B, it is plain that, if the latter be the driving wheel, the motion of A will be reversed; or if A be the driver, that of B will be reversed. On the question of a substitute for the chain, see new query on this sub ject.-E. L. G. [4504.]-ELLIPSOGRAPH.-A slightly different plan of drawing ellipses is shown in the accompanying figure. BCB is a flat bar, grooved along a vertical B edge, CO is a rod, pivoted at C, a fixed point in the bar, and at O to another rod V O U, which passes under it at O, and who se extremity V runs in the groove in the edge of the bar; CO is equal toV O, and at some point P in V U produced the pencil is fixed. The under slide of the bar B B' may be furnished with steel points, to fix it in position on the paper. Then by the revolution of the rod C O about C, while the extremity Vof the other rod traverses the groove, P traces out an ellipse as indicated by the dotted line. This is based on the same principle as the "trammel," viz., that U V is constant; PU is equal to the semi-axis minor of the ellipse described, that is, to BC; and PV is equal to A C the semi-axis major. One disadvantage of this plan (as of the trammel in certain cases), is that only half the ellipse can be described at a time. But if two steel points, such as were spoken of, be fixed in the bar at equal distances from C, then by removing the instrument and placing it so that these points interchange their positions, each going into the hole in the paper which was formerly occupied by the other, the second half of the curve may be described without much additional trouble. Another disadvantage is that, in consequence of the finite breadth of the bar, the semiellipse will be left incomplete over a short space at each extremity of the minor axis. But this part of the curve might, with what in most cases would be sufficient accuracy, be filled in by hand; or the difficulty might be got over by providing notches in the bar at the places where O and P fall upon it, so as to allow the central line of each of the rods, when in their ultimate positions, to coincide with that of the bar; or, again, by abolishing half the bar, and drawing the ellipse only a quarter at a time. Any mathematical instrument maker could fit a contrivance as the above with shifting pivots, like those mathematically true, it describes a beautiful curve, so this (Sept. 9), I assumed, of course, "length of the line," [4665.]--MATRICULATION PROBLEM.--In answering to mean "length of journey," because it needs no mathematics to show that where the question names no unit of length, or of anything but time, time alone can be determinate in any answer. But the problem is not of answer. It has only one answer-five hours.-E. L. G. "indeterminate," as this implies one admitting variety the vessel, plus the assumed slip in feet per minute, by [4692.]--SCREW PROPELLER.-Divide the velocity of the number of revolutions the screw is intended to make miles per hour, the slip two miles, and the revolutions of screw in feet. Suppose the speed of a vessel be ten the screw 120 per minute, then 10 miles per hour = 880ft. per minute, and 2 miles = 176ft. per minute; 880 + 176 120 8.8ft. pitch.-ESPERANCE. [4704.]-CHANGE OF SURNAME.-It is necessary to find whether the desired name is borne by any of the nobility, as in that case you cannot assume it without the leave of the head of the titled family: thus a person lately complained of great expense he had incurred at the Herald's office to change his name to Brown, which, after all, they were unable to confer on him. Of course it would be equally impossible to usurp that of Herbert or Howard, and Mr. Bugg never did so, but invented the totally new name of "Norfolk-Howard." I would advise the present querist to be more inventive. Our names are far from from being too numerous.-E. L. G. [4760.]-EXPANSION OF STEAM.-If I wanted either the hyperbolic or the dual logarithm of any complex number I should, as the quickest way, take its common tabular (or Briggsian) logarithm, and multiply it in one case by the hyperbolic logarithm of 10, in the other by dual logarithm of 10. The dual logarithm of 10,-correct to 8 figures, which I cannot now turn up,-will be 1 (2) It is no blame to the ENGLISH MECHANIC to 30103 say that a table, such as " A. W. E." desires, would be certain to be misprinted, as certainly as the same amount of "cryptograms," and more so than algebraic formula. Instead, therefore, of any tabular figures I will put him in the way of computing them for himself. The kind of logarithms most easily found are the hyperbolic, and through them we arrive at all others; but in no system are the logarithms of whole numbers obtainable directly. They must be built up, as it were, from those of fiactions. Thus the log. 2, of any system, will be the sum 34 of the log arithms of and of because = 2. Now the logarithms of fractions are found with less labour the nearer the fractions are to 1 (or the logarithms to 0) and is really the highest number whose logarithm we need obtain directly. The rule is to make a new fraction from the difference and sum of the two parts of that whose logarithm we seek. Thus from make There only remain the two flat-ended beam-compass [4605.]-OLD MICROSCOPE.-If "F.'s" old micro- [4616 & 4792.]-PROBLEMS; RESOLVING A FORCE INTO TWO EQUAL ONES AT A GIVEN ANGLE. = 2 8-2 1 5 will be half the hyperbolic logarithm of ginning our operation on 2 instead of 1, to save the need 4 8 This, added to the above,gives hyp. log. 2; or added to twice the above, it gives hyp. log. 3; or the same if we subtract it from twice log. 2, that is, from log. 4, because 4÷ = 3. Thus, with these two, you get by addition only the hyp. logarithms of 4, 8. and all powers of 2; of 9, 27 and all powers of 8, and of 6, 12, 18, and all intermultiples of such powers. But now, to get the log. of 5, or of 10, 15, &c., we have either to compute that of and add it to 6 5 4 those of 4, 8, &c., or compute that of (which is easier) 5 and subtract it from those of 6, 12, &c. So " A. W. E." will now seelthat, if he would deduce from the hyp. log. of 4-75 that of 47, he has but to compute and substract from the former that of or of (which is very easy because 94 4.75 4-7 95 [4788.]-DISSOLVED BONES. -For my garden or field I should prefer the bones crushed into pieces about the size of a hazel nut, or ground to powder. I should mix these with all other manure produced in the establishment adding sufficient drysoil to absorb all moisture. To be kept under a shed and turned over frequently. This was the plan I followed when living in the country and enjoying the pleasures of a large garden and some acres of meadow adjoining. Nothing was wasted, and the ample crops of fruit, grass, and vegetables well repaid our trouble.-H. B. M. [4790.]-COPYRIGHT.-All printed matter should be form can be obtained for one penny; trade marks are registered at Stationers' Hall, London, where the proper also registered there. For the registration of designs the office is at Whitehall.-H. B. M. angles, the problems can be put in the following form:[4792.]-PROBLEM.-Observing the supplementary (a) the chord of 120° is 100 (or the sinus of 60° is 50), what will be the radius of the circle? Tables give sinus 60° 0.866; hence 0-866: 50:: 1: R=57-6 (b) Chord of 150° is 100 (or the sinus of 75° is 50), what will be the radius of the circle? of A B with your scale, and that gives the answer read inf. quired. If you want to calculate it, say as Sin AB E: sin BAE:: AE: BE. In first example Sin 60°: sin 30:: 50: B E, or by a table of natural sines 1 1 1 + -+ 1 x 2 1 x 2 x 3 and is commonly called e. Now as it is the principle of the Briggsian ones to make 1 the log. of 10, as soon as we have the hyp. log. of 10 we can get all Briggsian logarithms, because every number's Briggsian log. is = its hyp. log. x So likewise, its dual log. is hyp.log. 10 hyp. log. 2 1 = its hyp. log. x 1 These multipliers, are called the moduli of hyp. log. 10 hyp. log. 2 Briggsian or of dual logarithms, and are the log. in each system of that number whose natural log. is 1, namely Hence "A. W. E." will see that had we begun the above operations by dividing not 2 but the double of one of these moduli, namely of e. 2 or 2 hyp. log. 10 hyp. log. 2 we should, from the former, or 86858896. 5.., have got Briggsian logarithms, or from the latter, = 2.88539008 have got dual ones; and this is the easiest way of computing either. (3.)' No; but see Rankine's "Manual of the Steam-Engine, &c.," 1859; or his "Useful Rules and Tables," 1867.-E. L. G. [4765.]-PISTON AND PRESSURE.-"One's" engine appears to have three pistons, so fixed on one rod that their intervals are unalterable. He admits steam around A, one of the smaller ones, and between it and the largest, so that, by its excess of pressure on the latter, both are carried forward, and "so far all right." Of course he is right that the large piston has "the same pressure on it as though the cylinder A were omitted;" but what of the pressure on the face of A itself? I should have said that, as he works solely by the difference of these pressures-namely, that upon the margin whereby the big piston exceeds A, the waste of the steam between these two pistons, and of all the iron employed in giving cylinder and pistons this enlarged size, as well as of grease and friction around A, was so far all wrong: but I am only-ANOTHER. [4766.]-STAUNCHING TIMBER JOINTS.-If your canoe is yet to build, paint the laps with good white lead as you fix them; and if they are clenched, or what is, better riveted with copper burs, every 24in., you will find the joints quite water-tight and sound. If it is built, and is worth the trouble, brush into the joints as much white lead as you can get in; do this outside and inside, and re-clench or re-rivet every nail anew; then before the lead paint hardens press or jam in as much good boiled oil-putty as the joints will receive; when that is a little hard you can paint over from time to time and you will have no leakage.-S. H. [4768.]-PLASTER OF PARIS.-Plaster of Paris is not hard enough to polish. If some alum is mixed in the water used, and the plaster when dry soaked in stearine or wax, a piece of cotton as a rubber when cold will give it the best polish it is susceptible of. When some mode of hardening plaster into the consistence, say of marble, is discovered, it will be a great boon to artists, and an invaluable means of disseminating art. Ransome's silicating plan is applicable only to more porous material. It is too glutinous to enter the pores of fine plaster.-C. DEVANT. [4771.]-BRASS CASTINGS.-Borax is the only flux used by brass casters. But there are many causes which produce imperfect castings. The metal being too hot; too cold; the zinc or tin having been, perhaps, all burnt away in previous meltings; the insufficient means of escape for gas, air, steam, &c., from the moulds. 4771 will save money by getting some brassfounder (try for one in sixpenny column) to show him how to do it. An intelligent expert, in a melting mood, will teach him more in a day than he will find out for himself in a year.-C. DEVANT. [4775.]-LUMPS ON HORSES.-Let him first give the horse a bran mash, and on the following day give a dose of physic ("aloes "); the animal must have rest until the effects have passed off, and let his diet be sloppy until the lumps disappear. With regard to the broken lumps, apply two or three times a day the following lotion:-Sulphate of zinc, 2 drms.; water, 1 pint. If there are many broken lumps under the collar get it lined with linen.-VET. 502+ 13:42 = If you have not a table of natural sines you can work the sum out by logarithms, which again you need not do if you have a table of squares and square roots to help you, as you can find the natural sines from the logarithmic ones by looking out their values in the table of logs. of natural numbers. The first plan with a scale is near enough for many purposes.-J. K. P. [4795.]-ENAMELLING SLATE.-The patterns are painted in spirit colours, varnished and hardened in a stove. Many of the imitation Greek vases are done in the same manner, especially those with black ground. In Warwickshire, I have seen stone chimney-pieces, after having been fixed, rubbed repeatedly with linseed oil until the stone would absorb no more. They were then varnished and rubbed to a brilliant polish, which brought out the veining of the stone and looked exceedingly well.-ENGRAVER. [4796.]-UNIVERSAL SWIVEL GAS-JOINT.-Perhaps the friend who requires information respecting the above will be able to understand from the enclosed sketch. The swivel shown is a single one, having swivel will be two single swivels either made purposely, a horizontal motion from right to left. A universal or for temporary purposes, coupled together by a nipple screwed inside the outlet A; the second swivel would be screwed to the one shown in the sketch in such a section of boiler and pipes; Fig. 2, plan of top of boiler. They are not drawn to scale.-R. B. [4807.1-REFLECTOR STAND.-It has for many years been a crotchet of mine that all mounting of reflectors of 6in. aperture or greater should be superseded thus:-Fix the speculum and tube (if any) permanently looking to the upper celestial pole. On the tube's mouth which must be shorter by about one diameter than the focal length), or at the corresponding place if there be no tube, a ring or collar, fixed in an equatorial plane, must support another turning in the same plane; and perpendicular to this plane must rise from the turning collar two cheeks or arms to bear, like a dressing-glass, an elliptical flat of plate glass as wide in the minor axis (on which it is to turn) as the speculum, and twice as long. I have no doubt that about the centre of most of the manufactured plates of 16ft. by 8ft. portions may be found sufficiently plane, though small pieces could never be ground separately true enough. The internal quality of the glass would matter no more than in the speculum, both being silvered on their faces. The centre of this flat to have a small perforation through which the rays proceed to focalize just above it, the nearer the better; and to be viewed through a fixed eye-piece looking towards the depressed celestial pole,-in this latitude about the direction we fix microscopes by choice. The telescope then would be Newtonian, with this difference, with no motion of anything but the flat glass, you can that rays are turned by the flat reflection before convergence instead of after it. The advantage is that, bring equally into view any object whose North Polar distance exceeds 60°, and then follow it with no motion but that of the collar and what it carries. The speculum and eye-tube are alike fixtures. For objects within 60° of the elevated pole it would be better to reverse the whole arrangement and look towards that pole, but the above more compact and easy fixing would in all latitudes give us the command of the solar system and all the more interesting half of the sphere.-E. L. G. had better put £2 more to his £3 and buy Solomons' £5 [4808.]-THE TELESCOPE.-"Amateur Astronomer" telescope rather than spend it on attempts to produce one himself. He will then have the foundation of an excellent instrument with a power of 40 day and 80 astro., with which good and interesting work may be done; and extra powers of from 20 to 250 can be added according to convenience at any time. The day power of 40 will give admirable views of the sun; and discs of blue and green glass (light and dark) roughly cut may be obtained of any plumber, to lie inside the eye-hole, for a few pence. Afterwards revolving glasses, 6ft. stand, &c., can be obtained. The short tripod-stand can easily be secured to a 5ft. stool, and "Amateur Astronomer better exercise his ingenuity on this, and a few other requisites, and he will find himself well started at a small expense.-AMATEUR. had [4810.]-LARD AND SAUSAGES.-For rendering down lard, nothing is better than a bell-metal skillet. To prevent burning, a hot plate is preferable to an open and wring hard. Respecting sausages see 4800, Vol. fire. To press the "scraps enclose in a coarse cloth XI. p. 618. Much depends upon the seasoning, and care should be taken to use sufficient fat to prevent them heating dry.-PATERFAMILIAS. [4813.]-SMALL PLANING MACHINE."Tometer" cannot be taught pattern making by any amount of printed instructions; his only way is to go into a workshop and study there. Planing machines have been already fully discussed in "ours," and "J.K. P." has, en page 99, Vol. X., furnished drawings of as good a one as could possibly be desired. As I happen to be working in the same direction as "Tometer, "and have begun to prepare the drawings of my machine, should that gentleman reside in London, and feel disposed to communicate with me,we to work out the patterns together [4819.]-SCIENCE QUESTION.-Locus of (y - 2)2 + (x - √2)2 = ? Comparing with (ra)2 + (y-3)2 tions," No. 79). I see the locus is a circle, the centre of =R2, equation of a circle, (vide "Salmon, Conic Sec 2, x = 2, and radius which has for co-ordinates: y = 4/2 1,187.-BERNARDIN. = manner as to have a vertical motion up and down; this may possibly arrange would be a suitable joint for any purpose where there is-S. STEVENS. an unevenness in ground, or even where there is an oscillation, and it is easily obtained from any maker of number, is a first-class joint, but would have to be made gas fittings. The cup-and-ball joint, as shown in a late specially. The plug of the swivel is cast hollow, with an aperture for inlet or outlet, and a groove turned in it right across the steam or gas-way; this allows a free passage at all times. The telescope joint will explain itself. A is the outer tube with stuffing box, B the inner tube, C ring for keeping down packing, D cap. This is a simple arrangement, that any one who has lathe, and has been accustomed to turning and screwing, ca n make in a few hours.-D. CLARKE. [4797.]-TUB-HOOPING." Anon" could easily get the size of his hoops by marking the equal spaces on the tub where the hoops are to be placed; then take the measure with a piece of webbing or stout tape, leaving enough to lap for two or more rivets. The tapering is done by hammering one edge with a thick-paned hammer, to stretch or cause that side to expand, leaving the other side the smallest.-J. MOSELEY. SEPT. 30, 1870.] ENGLISH MECHANIC AND WORLD OF SCIENCE.-No. 288. Diffusion of Useful Knowledge, (48.), a good book; also with crocus.-J. MOSELEY. As to [4825.]-ELLIPTICAL CUTTING FRAME. TO "J. W.J.-You could, I think, obtain a picture of the above by applying to Holtzapffel's at 64, Charing-cross, but it is a toy, merely, like the rose-cutting frame, and not at all the thing that any one but a very aristocratic ornamental turner would think of laying out his money on. I never made one of the first mentioned, but did make A very considerable part of the latter for a friend who had coramenced it, and was gone on a voyage. its usefulness, I may say that I never tried it more than once, just to see that it would "gee;" and I have never seen a single specimen of any work that he did with it since, during the 10 or 12 years that it has been in his possession. The fact is, that you can ornament flat surfaces only with these things, and you cannot turn an oval, such as even a bradawl handle; so the thing is useless.-J. K. P. [4830.]-DIAMOND POINTS IN DRILLS.-I have used these only for drilling china and glass. My method is as follows:-Select a bit of cork the size required, fit into a small brass or tin tube as tightly as possible, keeping the point in the centre, then fasten with a very little solder on the end of tube, to prevent the point falling out. I have frequently managed to make it sufficiently tight without solder.-ENGRAVER. bessi, or Waroe-assay, Sumatra, Borneo, &c., Intsia am- Iron Pao Robinia panacoco and tomentosa. Ironwood, Antilles, [4838.]-PEDESTRIAN TOURS.-By all means take Salisbury in your way; you will be gratified by the will be enraptured with the holy calm that reigns extensive views of the breezy downs, while your friend around and in the grand old cathedral. From the eight springs), a magnificent prospect is obtained. I may here doors (the top of the tower whence the fairy-like spire mention that from there, with Steward's "Lord Bury, No. 8 A," I could read an inscription in Harnham churchyard. I saw the Chapter-house some years ago, beautiful even in its ruins, but now, as restored, one of the most glorious buildings I ever beheld. Nothing overdone, yet ample decoration pervaded by a chaste loveliness, "A thing of beauty once seen to be never forgotten. Admission to the whole of the and a joy for ever." Cathedral, 18.-AMATEUR. [4840.]-GUNPOWDER.-I do not suppose that, at the time Mangnall wrote his "Questions," either he or any of his contemporaries were aware of the fact that the Chinese were acquainted with the use and effects of gunpowder long anterior to its discovery in Europe during the 13th century. Indeed, if I mistake not, the latter circumstance was made known in Europe, for the first time, during the decade 1880-70. It is very difficult, Roger Bacon in his amongst the various contradictory accounts, to affix any treatise, "De Secretis Operibus Artis et Naturæ et de precise date to this invention. Nullitate Magis," cap. VI., published at Oxford, about we are able to make a fire that shall burn at any distance 1216,informs us that from salt petre and other ingredients, we please, which" other ingredients" it appears from some of his other manuscripts were sulphur and charcoal. Robins, in his "Gunnery," considers it as known before the time of Bacon, and that this philosopher mentions it not as a new discovery, but as the application of an old principle to military purposes, to which it had (4832.) ON ZINC, TIN, ETC., FOR not been before employed.-S.. - PAINTING BATHS.-Your correspondent should apply the ElectroMordant to his metal bath, which is sold at 4, Ogdenstreet, Hulme, Manchester, when he will find the paint adhere most tenaciously.-C. LECKIE. [4830.]-DIAMOND POINTS IN DRILLS.-"Holtare zapffel," pages 178, 179, says the pieces used selected from imperfect stones or chips of the same, known as bort, mostly fixed in brass wires by first drilling a shallow hole for the insertion of the stone, which is imbedded slightly below its largest part, and the metal is pinched round it. Shellac is also used for cementing them in, and spelter or tin solders may be fused around them with the blowpipe, but pinching them in annealed brass is preferred." Of course no solder can be made to adhere to the stone, although the stone itself will bear an intense heat without damage. The action of all solders is to alloy the respective metals that have to be joined, to a very trifling depth, just as glue penetrates to a very small depth into the surfaces of pieces of wood that are afterwards rubbed together to exclude air as well as all the glue that can be get rid of by so doing.-J. K. P. [4830.]-DIAMOND POINTS IN DRILLS. - First drill or cut a hole to receive the diamond, then burnish the projecting edges of the metal down on the diamond in the lathe. This will hold with perfect safety. ANGUS. R. [4840.]-GUNPOWDER.-It must not be forgotten 45 3.8751462, to find the number. Referring to the tables we have log. 8751423 = 75014, subtracting this logarithm from the given logarithm, we have 39. In the last column of the tables we have the tabular difference 58, hence see Chambers', p. 7, explanation, divide 39 by 58, for the remaining figures.-T. S. H. [4851.]-AEROSTATICS.-The compressibility and expansibility of air may be said to be unlimited; theregreater compressibility or expansibility. If we take a fore there is, practically, no other fluid which possesses tube, 12in. long and lin. diameter, with the bottom sealed, and a perfectly air-tight plug at the top, the to 15lb. If we put 15lb. weight upon the plug it will pressure of the atmosphere upon the plug will be equal descend in the tube 6in., squeezing the 12in. of air into 6in., at which point the plug will have upon it 30lb., that is the 15lb. weight, and the weight of the atmosphere, will squeeze the air into a space of 2in. Now, the 75lb. which is equal to 15lb. If we put 75lb. upon the plug, it is equal to 5 atmospheres; added to the weight of the atmosphere itself, make together 6. If we divide the 12in., the result is the number of inches into which the air is The weight of the the length of the tube, by 6, the weight upon the plug, compressed. In like manner 24 atmospheres will reduce external atmosphere must always be included in the the 12in. to half an inch, and so on. weight upon the plug. With expansion, it will be observed that air in its natural condition around us has an elastic force of 15lb. to the square inch. If we suppose the 12in. of air in the tube to be so expanded as to fill 24in., its elastic force would be reduced to 71lb., 36in. 5lb., and so on to any extent. We see the 36in., to which the air is expanded, contains the original 12in. three times; so if we divide the original elastic force (15lb.) by 3, we get 51b., as the elastic-force of the air when expanded to 36in.-J. BUTCHER. [4852.]-SWIMMING PADDLE.-I have lately been trying some experiments with a swimming paddle shaped like an oval hairbrush. I find it of little or no use in swimming forwards in the ordinary way; but by lying on my back and working a paddle in each hand, after the manner of sculling a boat in the stern, I find I can get up a speed backwards attainable in no other sides.-S. P. J. LIZARD. way. The arms should be kept straight down by the DRIVING.-In reply to [4859.]-LOCOMOTIVE "Steam Rider" the jerking he mentions will occur and engine, and from causes over which the best of drivers or firemen have no control; as when the rails are not be attributable to either the driver or fireman of an damp, but not thoroughly wet, they are then in a very slippery state, and the wheels of the locomotive will not properly bite, consequently when the regulator of the engine is open the wheels will revolve at a great speed, but the progressive power of the train will be diminished; the driver is then obliged to shut off the steam, and open the sand pipe to sand the rails and cause the wheels to would be brought nearly to a stand, and the engine bite. If he kept the regulator open, in time the train would, in all probability, be greatly damaged. The jerkting of the regulator alternately. Jerking will also be caused by the couplings of the carriages not being proing in this instance is caused by the opening and shutThis will allow the carriages too much perly and tightly screwed up; or if they are properly play and cause them to oscillate, which will be very unscrewed together and not tightly screwed to the tender of the engine. [4833.]-TO RENDER CALICO AIR-TIGHT AND WATER-TIGHT.-Make a dough by dissolving indiarubber in coal naphthațin the proportion of 14lb. aphtha to 1lb. of best Para rubber. Spread this dough on your calico as thin and as evenly as possible; put on five coats; double the cloth together, having the rubber in side, and you will find it will be thoroughly air-proof the nitre and sulphur may be superseded, but in no case comfortable for passengers; whereas, if the train is and water-proof.-AUGUSTINE. [4837.]—FOREIGN WOODS.-In reply to "Lignum Vitæ," in your last, I may state that he will find it very difficult to obtain detailed information respecting the various woods about which he inquires. In the year 1855 and 1856, I contributed a series of articles on Colonial woods to the Building News, having been officially connected with all the Great International Exhibitions. I made it a point to collect samples and all the published information possible, about various colonial and foreign woods, and the special catalogues and the reports of the juries contain much valuable information. I had thought at one time of bringing out a work on the commercial products of the forests of various countries, for which I have ample information, and there is no book on the subject, but I doubt if much sale could be obtained for such a work.-P. L. SIMMONDS. cealing in his anagram.-E. L. G. the carbon-the element our mouk thought worth con- [4842.]-LAND QUESTION.-If this were given in N at A and D; giving me the measures of these, and at [4843.]-MUSICAL-" D. N. E." will find "Think of [4837.]-FOREIGN WOODS.-This query requires a long reply, many woods being named in it. The inforabout woods are in hundreds of reviews, mations botanical works, catalogues of exhibitions, &c. I will try to give some particulars about those mentioned by "L. V." This time I only speak of the American woods and of the different sorts of iron wood; the notes on American woods I took principally from catalogues of the Canadian produce at the London and Paris Exhibitions; the details on iron wood I took from my own notes collected from numerous works on foreign produces. In a future number, if my spare time allows it, and Mr. Editor thinks the matter worth the space, I will say a word more about the other woods mentioned by the querist. 1. American Woods.-Elm, rock elm, Ulmus racemosa, found in Canada, &c., averaging 150ft. in height; much used for keels of vessels, piles, &c.; specific gravity 0-59. American or white elm, Ulmus Americana; wood tough and strong, used for the naves of wheels, and preferred by wheelwrights to the English elms. Black oak, Quercus tinctoria; one of the largest trees of the American forests, 100ft. to 180ft. in height, 4ft. to 6ft. in diameter. The bark used in tanning, and for obtain[4843.]-MUSICAL.-"D. N. E." will find in "Gospel ing quercitron, used in dyeing. White wood, Liriodendron tulipifera, growing in Canada, &c., 130ft. in height; Sounets," by Rev. Ralph Erskine, of Dumfermline, what words "Thus think, and smoke tobacco." It is also He died a hundred called also tuliptree, and sometimes, erroneously, yellow I think he wants-a poem each verse ending with the poplar. The wood is extensively used as a substitute It is easily published with his other works. for pine for building and cabinet purposes. made wrought, durable, and susceptible of a fine polish; years ago.-W. FABER, Inverkeithing. [4846.]-LOGARITHMS.-Has not "Work" specific gravity, 05. Mangrove of Trinidad, Rhizophora some mistake with this question? According to his data Mangle; wood used for making sugar hogsheads, and the number must consist of four whole numbers, and not Does "Work" for ship building; bark for tanning. 2. Iron wood is a general name given to many trees, producing hard, a decimal, as given in his answer. ponderous, close-grained wood; I forward a list of the meau 3-875, &c., instead of 387, &c. ?-C. H. W. B. [4846.]-LOGARITHMS.-Subtract the logarithms, principal of them, with their common and scientific names and their native countries. Iron Woods (a) of divide the remainder of the one 39, by the remainder of the Indian Archipelago.-Kajoe manbouf, Bantam, &c., the other 58. The quotient 67 annex to the natural The last logarithm should be written Pahudia sp. Oenglen or belian, Sumatra, &c., Eusi- number 75014. deroxylon Zwageri, T. and B. Nani-meira, Moluccas, Nania rera, Mig., a precious wood for maritime construc and printed, 3-8751462, and the negative index 3 shows 007501467. It is, in fact, a proportion sum tious. Kajoe Djocar, or iron wood of the west coast of two noughts must be prefixed, it then becomes log. Cossambie, Capania 8751462 Cassia florida, Vahl. In other words, given the logarithm sideroxylon, a very useful wood. Linggoen, Ceram, in decimals stated thus:-If 0000058 give 1 what will Pterocarpus sp. Iron wood of Moluccas, Inga sp. Kajoe 0000039 give? Sumatra, the train steady. Again, if the engine which is attached tightly coupled together, the weight of the engine holds to the train has not a balance weight fixed in the driving rod, it will cause a very great amount of jerking; as when the side-rod is descending the impetus of the engine wheel to counterbalance the weight of the crank or sidewill be greater than when it is ascending, consequently the complete revolution of the driving-wheel will cause two distinct jerks to the train it is drawing, which is very annoying, and especially when the train is running at a high speed. Most likely this is the kind of jerking which "Steam Rider" has noticed.-AN OBSERVER. [4862.]-SUGAR OF LEAD POISONING.-I officially visit a large manufactory of white lead where the firm have on the premises a constant supply of lemonade made from the subjoined recipe, and the workpeople can drink the lemonade whenever they wish, at any time of day. In addition to this, all persons are required to wash their hands before leaving work, for which the firm provide every requisite:-Sulphuric Acid Lemonade: 1 dozen lemons, 7lb. of sugar, 14oz. (fluid oz.) of strong sulphuric acid, 20 gallons of water. This is fermented with yeast, and becomes a pleasant acid beverage. The active principle is the sulphuric acid, which acts upon the lead and forms an almost insoluble sulphate of lead. As lead is largely absorbed by the skin, it is of the greatest consequence that the skin be kept free from lead by frequent and effective ablutions, rendered all the more necessary from the tendency which lead has to accumulate in the system; and, for a long time without being suspected. I believe contherefore, lead-poisoning may be going on insidiously stant unremitting cleanliness, with the daily use of the sulphuric acid lemonade, to be the best antidote to lead-poisoning.-GEO. H. L. RICKARDS, Factory In spector. [4862.]-LEAD POISONING.-In reply to "W. E." these are antidotes for poisoning by sugar of lead:Phosphate of soda, Epsom salts, plaster of Paris, aud Glauber's salts.-S. J. ROSE. [4865.]-LACQUERING BRASS WORK.-"Stick-inshould be brushed quickly, as it dulls on cooling. He must use the lacquer very sparingly; the lacquer is no the-Mud" did not heat his work hardly hot enough; it doubt all right; it requires practice, but he need not despair.-J. MOSELEY. [4865.]-LACQUERING BRASS WORK.-There are various methods of finishing brass; as, by turning and polishing on the lathe, finishing with the file and burnisher, or covering with a coat of coloured lacquer, immersing it in a bath of acid. Oftentimes portions of brass which we wish to ornament cannot be finished in the lathe, or will not pay the cost of hand-finishing. We may cast such portions of the required forms at once, and then produce a beautiful surface most indipping acid." This bath is made by mixing together nitric acid, sulphuric acid, and muriate of ammonia, or geniously and cheaply by immersing it in a bath of oil or grease, may be heated to consume such grease, sal-ammoniac. The work, if it has been in contact with and it will then be discoloured and dirty; it must be pickled in a bath of dilute nitric acid, which may be one part of acid to three or four of water. The articles must not be permitted to remain too long in the pickle, as injury will result by the acid eating holes in the work. To clean the surface of the metal is all that is required. Remove the articles from the pickle, and wash them clean, so as to remove any adhering dirt and the acid in which it had been immersed. The dipping bath is composed mostly of nitric acid, the sulphuric and the muriate of ammonia being present in inferior quantities. There is no certain rule to mix them. Much depends on the concentrated character of the acids. A little experience will enable the operator to judge for himself of the proportions he needs. Strong nitric acid alone will do, but many prefer to add a quantity of other ingredients. The mixture should be so strong that a momentary immersion will be sufficient to make the work bright and clean, no matter how rough it may be. Remove the work from the bath, and immediately plunge it in cold water and wash it well to remove the acid, and give it a final and thorough washing in hot water. If a little crude tartar be added to the hot water, it will more effectually remove the acid. To dry the work it may be embedded in fine hot saw dust. The surface produced is beautiful, and may be protected with a coat of clear varnish or lacquer; but without the lacquer the surface will be retained for a long time, and withstand considerable wear and handling.-G. VALENTINE. [4866.]-WATERPROOFING TIMBER ROOFS.-I have made a very good waterproof roof by covering the rafter with thin boards and laying on a coat of coaltar. I then covered the boards with sheets of brown paper before the tar dried, and laid on another coat of tar, sifting over it some fine sand or cinder dust. This makes a thoroughly waterproof roof, and is very cheap. SAUL RYMEA. [4869.]-PENDULUM.-In answer to "Electro Magnet, No. 1," if you want a pendulum to beat two seconds, it has to be four times as long as a one second one; also, if you have a pendulum beating two seconds, say, 15ft. long, and you want one to beat one-third of that, it must be one-ninth part of that length. So the whole resolves itself into this:-Having the length of a one second pendulum, which Dr. Denison gives as 89-1893in., you have to take four-ninths of that length for your second pendulum. Denison says, moreover, that "if the expansion of wooden rods could be depended on the simplest of all compensations would be a wooden rod with a lead bob 14in. long." "Electro" must remember that the length is not measured to the bottom of the bob, but to the "centre of oscillation," which is somewhere rather more than half way down such a bob as he proposes to use. Denison is averse to putting brass cases to lead bobs, as it increases the diameter and resistance of air and the expense more than it does the weight, which is a great thing. I should think lin. diameter and 7in. long better than 2in. diameter and 4in. long; either way it must be supported from below; not have the rod fixed to top of bob. Mine is 3in. din meter and 8in. long on a one second pendulum, and weighs 22 lb., with a in. hole through the middle for the rod to pass through, the total length being 432in. from the bottom of chops to bottom of bob. In casting your bob, don't do as I did, viz., use lead and solder mixed (being the lining of an old sink), particularly if you manage to introduce (as I did) some rosin, using a bright iron bar as a core for the hole down the middle. My result was a fine solid bob, stuck so tight on the central core that I had to melt it off again. I should think mahogany that has the appearance of the socalled cedar that you see cigar chests made of, or still better a great deal, hickory, would be the stuff for a rod. Any gunmaker or fishing-rod maker keeps hickory in stock sufficiently long for what you want. Still no doubt deal will do very well. 9-32 diameter of hickory or 5-16 of deal should be ample.-J. K. P. [4869.]-LENGTH OF PENDULUM,-If the train of wheels in the clock movement of "Electro-Magnet, No. 1," is really calculated to make 90 beats per minute, the pendulum should be 17:422in. long, measuring from the point of suspension to the centre of the ball or bob. If with that length of pendulum the clock does not keep correct time, the train is not as described, in which case if" Electro-Magnet" will give the numbers of leaves in all the wheels and pinions, I shall be glad to give him further information.-THOMAS ARMSTRONG. [[["Clock Pivot" has given a similar answer.-Ed.] [4882.]-VIBRATING CONTACT BREAKER. - It may be made to vibrate many hundred times in a second. It depends on the proportionate resistance of the spring and weight to the power of the magnet and the purity of the iron in the magnet and armature which enables the magnet to be formed and discharged with little resistance. The rate of vibration may be ascertained by the musical note produced.-SIGMA. [4883.]-MAGNETO-ELECTRIC MACHINE." A. Sutherland" is working on a delusion. Unless his magnetic machine is very powerful, and the coils of large wire, he canot hope to generate an electro-magnet with the current it gives off; as he will see, if by means of a galvanometer he compares this current with that of the few galvanic cells" he expects it to do the work of.-SIGMA. [4887.]-DIATOMACEOUS EARTH.-Perhaps Dr. Carpenter's recipe will answer "F. G.'s" purpose. It is to first wash the earth several times in pure water, which should be well stirred and the sediment allowed to subside several hours before the water is poured off. The deposit is then to be treated in a flask or test-tube with hydrochloric acid (muriatic acid or spirits of salts), and after the first effervescence is over a gentle heat may be applied. As soon as the sediment has subsided the acid should be poured off and another portion added, and this should be repeated so long as any effect is produced. When hydrochloric acid ceases to act, strong nitric acid should be substituted; and after the first effervescence is over, a continuous heat of 200° Fahr.should be applied When sufficient time for subsidence has elapsed, the supernatant acid must be poured off and a fresh portion added; the process being repeated so long as any effect is produced. The sediment is then to be carefully washed until all trace of acid is removed. This recipe will, of course, only apply to calcareous earths, organic deposits, as guanos and the like. For siliceous deposits Professor Baily's plan must be followed. This is to boil the deposit for a short time in as weak an for some hours. alkaline solution as possible (carbonate of soda as well as anything). It must be borne in mind that this solution will act upon the frustule as well, though not as much as upon the cementing matter. "F. G." must not expect to attain to Mr. Topping's pitch of excellence "all in a hurry."-H. P. [4891.)-MATRICULATION.-In reply to " Inquirer," I may state that Todhunter's "Mechanics" is sufficient. for the above examination; but as it requires a knowledge of trigonometry, is not suitable for the beginner. Use Wormell's, published by Groombridge. For the chemistry, I should strongly recommend Gill's, published by Walton & Maberly; also Williamson's, published by Macmillan. Get up the former well before commencing the latter. For English literature read Angus and Latham; if time permits Marsh's "Lectures" and Shaw's " English Literature." The publishers of these are respectively Walton & Maberly, Longmans, and Macmillan. For French, get Baume's "Grammar,' or Schneider's. After reading these, and carefully working the examples, get Dr. Beauvoisin's "Anecdotes," (Marlborough), and for longer extracts, &c., any of the French classics edited by G. Masson (Macmillan). The whole of these works have been thoroughly tested by the writer. Let "Inquirer" recollect that no special French subject is selected; he is supposed to know that language nearly or quite as well as English. Practice translation from English into French; although not wanted for matriculation, it is the best way of making yourself thoroughly acquainted with a language.-C. H. W. B. [4892.]-CHEMICAL ACTION ON LIMESTONE."B. S." had better put his specimen under a gentle fall of water, intermitted by exposure to the atmosphere, and in time he will obtain his weathered encrinites." The geological student must learn to make full allowance for time when he attempts to follow in the footsteps of Dame Nature. A very weak solution of hydrochloric acid might aid our friend in his praiseworthy efforts.-H. P. [4895.]. ELECTRIC RESISTANCE. - The B. A. unit is the now recognized standard. It is impossible to define it satisfactorily without entering into a general discussion of principles which will be given in my series as soon as the description of the instruments necessary for it is completed. It is equal to 10,000,000 of Weber's absolute electro-magnetic units; practically it is 1-25th of Varley's unit, which is one mile of No. 16 common copper wire, and is as 1 is to 10456 of Siemen's units, which are 1 metre of mercury, 1 millimetr e in section at the freezing point.-SIGMA. [4896.]-SULPHATE OF MURCURY CELL.-The size of the elements depends on the nature of the work, but in general the plates are small, from 2in. square to three times that surface the carbon, the largest, because it requires to pass to the bottom of the cell or nearly so, in order to be well in contact with the mass of the salt; 5. The cost would probably be 4s. or 5s. 6. tion ne eded. 7. Its failings are that it only gives a small and fast-failing current, and therefore is suited only to special work; its advantages are considerable electro-motive force, little trouble, and no fumes. SIGMA. No atten [4898.]-NEPTUNE.-On the subject of the (by some) supposed ring of Neptune, "R." will find some information in "Hunt's Solar System," p. 137. Chambers's "Descriptive Astronomy," p. 160, (1867), says :-Lassel, Challis, and Bond, had at various times suspected the existence of a ring, but nothing certain is known on the subject.-G. J. W. [4899.]-THE MOON.-If "R." will observe what is the width (angular) of the apparent field of any telescope, rarely more that 30, he will see his question really has no meaning; for the eye and head must turn to take in successively the parts of an object of 150 diameter. Of course a telescope of the power named can only take in at once a portion of the moon, or of any object, about 6 of a degree wide; rather more, because the magnifying power applies not to the angle but to its tangent. The precise angle, the object subtending really 6, will appear to subtend, will be twice the angle whose taugent is 300 times the tangent of 3. This will not be so much as 900 evidently. It is as if you went 300 times nearer the object, which would make its half-width subtend 300 times the tangent it previously did, not 300 times the arc.-E. L. G. [4899.]-THE MOON.-"R." is right in his conclusion that a power of 300 makes the moon appear as if it covered a space 150 diameter in the heavens.-G. J. W. [4902.]-VARIATION OF THE COMPASS.-I think "North Pole " will find the variation given in that excellent little book-Gutch's "Literary and Scientific Register and Almanac." It is a pity that it has not the clearness and sharpness of type of years back. In 1866 the variation, I believe, was 20 25 W.-G. J. W. [4902.]-VARIATION OF THE COMPASS.-I was in the same fix as "North Pole," but found a table of approximate values in Symons's Meteorological Magazine (Stanford). Unfortunately I cannot recollect the date, but think it was a year or more since. The variation changes every month. and in different parts of England. I suspect at Greenwich now it is between 1930 and 20. S. C. [4910.]-POROUS CELLS.-The white. For full particulars, see No. 269, page 195, of last volume.-SIGMA. (4912.)-CRACKED GLASS.-Mix equal quantities of wheat flour, finely powdered glass, pulverized chalk, with half the quantity of fine brick-dust, and a little scraped lint, in white of eggs. This mixture must then be spread on linen cloth and applied to the crack of the glass; it should be dried before putting it to the tire.W. KIMMIS. [4912.]-CRACKED GLASS.-The only cement that Iam acquainted with, to stand the heat required, is finely sifted freshly burnt lime made into a paste. With this I have successfully repaired teapots, cups and saucers, and lamp glasses.—A READER. ing spirit for any purpose whatever, whether for sale or [4918.] ILLICIT STILL.-Any person manufacturnot, would be liable to very heavy penalties, unless licensed as a distiller.-A SUPERVISOR OF INLAND REVENUE. [4915.] Antoninus Pius, Emperor of Rome ;lworth about 1s, Gda.-W. J. EGGLESTON, - SILVER COIN. A silver denarius of [4916.]-BRASS COIN.-In answer to "San Sebastian," the coin which he has is a Chinese halfpenny; they are very numerous; value very triffing indeed.-H. J WARREN. [4918.]-BICHROMATE BATTERY.-The process of carbon connection is given in No. 272, page 269, last vol. (see also p. 388.) Brass wire is not so good unless large, as it is a much worse conductor than copper.-SIGMA. [4924.]-INSULATING.-The paraffined paper (see p. 2) answers excellently for condensers; it is superior to glass, which is, however, effective as in the Leyden jar. The candles melted down would do, if they are clear. Many of them are made of a mixture with stearine, which is not so good; but the material is to be got at any drysalter's, or dealers in oils, shellac, &c. SIGMA. [4926.]-TOMATOES.-A " fruit" is the "seed" of a vegetable. The popular use of the words is exceedingly vague.-H. P. [4931.]-CUTTING STONES.-There is no tool for this purpose equal to the lapidary's lathe. Illustrations of the machine, and a list of the various cutting and polishing materials requi red are to be found in Holtzapffel's "Mechanical Manipulation," Vol. III. This question has been many times asked and replied to in the ENGLISH MECHANIC, ride Indices.-A READER. [4932.]-BIOLOGICAL.-Let "A. T." consult any good physiological work, such e.g., as Carpenter's, and he will get a better knowledge of this distinction than from a short answer given in these columns. If "A. T." cannot get such a work, let him take a sheet of paper and write down in one column all the distinctive properties belonging to the higher forms of animal life, and in an opposite column all belonging to the higher forms of vegetable life. Above all let him notice the difference between the food of each, and the mauner of taking that food.-C. I. W. B. [4936.]-TEMPERAT URE OF PROJECTILE.-"Hon. Sec's." iron ball would have the heat augmented 206-942 Fahr. upon striking a target with a velocity of 1115ft. per second, supposing all the heat were conMotion," by John Tyndall, LL.D., F.R.S., &c., 3rd centrated in the projectile. See Heat a Mode of edition, pp. 43, 138.-C. W. STIDSTONES. [4940.]-MOSS AGATE.-" The name given to those kinds of agate which enclose dendritic or moss-like markings. Found in large quantities at Oberstein in Saxony."-Brande, "Dictionary of Science."-A READER. [4941.]-MARBLES-are made of various kinds of stone, by firstly cutting into cubes, knocking off the angles, finally rounded by being placed between revolving horizontal plates or stones. Not being a manufacturer, I quote this from memory, having hunted Museum shelves without finding my through the authority.-A READER. [4941.]-MANUFACTURE OF MARBLES.-The stone is first broken into blocks nearly square by blows with a hammer. These are thrown, 100 or 200 at a time, into a small sort of mill, formed of a flat stationary slab of stone, with a number of concentric furrows upon its face. A block of oak or other hard wood of the same diametric size is placed over the small stones, and partly resting upon them. This block is kept revolving, while water flows upon the stone slab. In fifteen minutes the stones are turned to what are henceforth termed "marbles." Agates are made into marbles by skilfully chipping the pieces nearly round with a hammer, and then wearing down the edges upon the surface of a large grindstone.-W. J. L. [4942.]-ALUMINIUM.-It is to be obtained of metal refiners, especially Johnson and Matthey's, HattonGarden, at 5s. per ounce. It is invaluable for surfaces of contact, when no spark is produced; equal to platinum, as to inalterability in the air. It is not only one-seventh the price, but as its specific gravity is so sinall, it covers three times the surface for equal weights. There have been many experiments as to the force and laws of electro-magnets, but I cannot at present indicate the best source of the information. With ample, that is, unlimited, battery power, a magnet might, I imagine, be made to sustain very nearly as much as the tensile strength of the iron would permit ; but it would hardly be a practical, that is, an economical proceeding. With a given piece of iron the force varies in the ratio of the quantity of electricity, called by some the intensity of current circulating; and if the wire is varied also in the ratio of the number of turns, these being best arranged to equal in resistance that of the battery.-SIGMA. QUERIES. [4943.]-DYEING AND SCOURING.-In the weekly issue of your most valuable journal dated June 29th one of your correspondents, writing under the initials of "J. K.," refers to Thos. Love's "Dyer and Scourer" as being a most useful work. Will J. K." say where I could obtain the book referred to, and what is the cost ?-S. G. [4941.]-HORSE'S HEAD.-Can any one explain to me the nature, construction, and use of the horse's head in the manufacturing of candles ?-TIMIRUNASUK. [4945.]-CYLINDROIDS.- Will some one of your kind readers of the MECHANIC give me some information about cylindroids? The sections obliquely taken of cylindroids, also the way of developing the oblique sections? All information on this subject will be gratefully received.-J. HOOPER. Tometer" for his kind reply to my query, 4694, p. [4946.]-SIZES OF WATCHES.-Many thanks to 620, the only misprint to it is that the printer has put 9 m's instead of inches; thus, 1m. 10; but if you will kindly refer to my query, 4440, p. 487, of Vol. XI. you will find it more explicitly put. I thought that there were 7 sizea of watches, viz., from lin. 10 8 size to lin.10 8 9 =20 size, and that they were thinking of reducing them to 9 5 5 sizes, viz., lin. 10 = 8 size to lin. 10 = 20 size, skipping 3 every size. A reply will greatly oblige.-B. E. LoDDY. [4947.]-SIPHON.-Will some fellow subscriber kindly give me a description of the siphon used for filling bottles? I believe they are used for that purpose, but should like to know to what extent.-D. U. F. [4948.] - SMOKING.-TO "SAUL RYMEA."-Smokers ought to thank "Saul Rymea" for his note, 357, in your issue of Sept. 19th. I am a smoker, and should be glad to learn if it is possible to get the entire paper read by Dr. J. Murray, at Newcastle, with the discussion. Could "Saul Rymea "inform me, in your next issue, if the paper is published, &c. ?-A READER. [4949.]-HEARING TUBE.-"Saxon" described one in the ENGLISH MECHANIC of January 28, but I cannot find that it is to be had in any shop. Will some kind reader inform me the best acoustic instrument to enable a deaf person to hear a lecture or concert, and oblige one who is-AS DEAF AS A POST. [4950.]-CEMENT.-Will any one inform me how to dissolve gutta-percha in chloroform, so as to form a cement for uniting broken china, &c. ? It is said to be the best for the purpose, and will resist the action of hot water, which no other cement will do.-W. G. [4951.]-WORKS ON CARVING.-Can any of your correspondents oblige me with the names of any good works on wood carving, with designs and the publishers' names?-CYMRO. [4952.]-TOOL HANDLES.-I should feel obliged if any reader would give me the name of the varnish (or mode of polishing) used on the best description of tool handles, such as Buck's ?-CYMRO. [4953.]-BURNISHING IRON, BRASS, Erc.-I should be glad of information as to the usual mode of burnishing iron, &c, and where the necessary tools can be procured ?-CYMRO. [4954.]-FOUCAULT'S EQUATORIAL REFLECTOR. -I was told, some six years ago, that the form of telescope described in answer to [4807] had been tried on a large scale by Foucault. Can any reader refer me to an account of this experiment?-E. L. G. [4955.]-MEDALLION MACHINE.-As I hear that a very clever medallion machine has been invented by a Mr. Lome, of somewhere in this district, could any of your readers inform me where I can see one at work, or who has one anywhere in Lancashire, or surrounding town?-EARLY BIRD, Bolton. [4956.]-LONDON.-Will any reader inform me if there is any plan of London published which gives a description of the soil in the different parts, whether gravel, clay, or chalk, and the heights of different spots above the sea level or Thames ?-2. [4057.]-MACHINE FOR WASHING CLAY.-Can any of your renders kindly inform me how I can make, or where I can see, a machine for washing clay free from stones ?-E. C. AUSTIN. [4958).- DISCOLOURED COIN.-I have a half Sovereign which has lost its colour, and turned nearly the colour of the Australian coinage; can any kind correspondent inform me how to restore it to its original colour?-SERGIUS. [4959.1-DYEING WOOLLEN.-I have a small piece of woollen which requires to be dyed brown; it is now white. Full particulars would oblige a reader.J. B. N. (4960.)-AMATEUR CLOCK-MAKING.-As winter draws on I expect to have plenty of leisure, which I have rather set my mind on employing in trying to make myself an 8-day clock to go with weights and pendulum. If any of your readers could givo me any information on the subject I should be very much obliged. I would propose to divide as follows:-1. An inexpensive work on the subject which shall give the number of teeth in the different wheels and pinions. 2. The tools required, their cost, and where to get them (I have a 5in. centre lathe). 3. Where to get the necessary brass castings and the teeth cut in the wheels; and about the cost of same?-IGNORAMUS. [4961.]-SULPHATE OF MERCURY BATTERY.-I am about making a sulphate of mercury battery, but before doing so wish to ask "Sigma" whether the mercury is likely to evaporate and prove injurious to the health, as I am acquainted with several looking-glass silverers who suffer fearfully from the mercury. I wish to know whether I could make a bottle battery and her metically seal each cell to prevent the vapour getting into the room, and could it be charged to last two years? -2. [4962.]-OXIDE OF IRON.-Will some of our chemical correspondents (who are also "practically acquainted" with the manufacture of iron) state their opinion as to why it is that if bars or plates of iron be rolled at a white heat the scales assume a blue colour when cold, whereas if the iron be allowed to become partially cold before the manipulation be finished, the scales when cold are red? Is a different oxide formed in each case? If so, what is the composition of the oxides? An explanation of the above will oblige several of my fellow-workmen, who are also fellow-subscribers. -FERRUM. [4963.]-HARMONIUM.-Having succeeded in making an harmonium of 2 sets of vibrators I find that two or three notes in the treble have a very wavy tone, as though the wind were of an unequal pressure, which cannot be, otherwise, I think, it would affect the other notes as well. Can any of your readers tell the cause, and sug gest a remedy, as it is a great nuisance, and greatly oblige ?-WAVE. [4964.]-LATHE.-Mr. Boord has kindly given the data asked for; but the inquirer doubts whether the pitch of screw on Buck's lathe has not been given as 10, by mistake for 9,-the latter being the usual pitch for the diameter in question, which in my lathe, by Buck, is 4th. Several of your correspondents have lately stated their views as to the most useful numbers for a division plate; but in none is the number 100 advocated. I have frequently required that number for dividing the heads of micrometer screws. How can this be done with the division plates in general use ?-AMATEUR TURNER. [4965.]-VERTICAL DRILL.-Will some one oblige me by a description with illustration of a vertical drill to be driven by a fly-wheel with handle? in. would be about the largest hole it would be required for.-R. T. [4966,1-VARNISH FOR SKATES.-Will any brother reader kindly inform me how to make yellow varnish for varnishing shates? I have tried it, but have failed. -CONSTANT READER. (4967.]-ELECTRICAL.-Will "Sigma" kindly ex plain a thing which puzzles me completely? The positive pole of my battery dissolves so in the sulphate of copper solution as, when moved, to make the solution turbid with reddish copper. The copper used for the positive pole is pure-electro deposited.-E. DEVANT. [4968.]-GEOMETRY.-Thanks to Mr. B. Fenby for his paper on "Reciprocal Geometry," which, with the assistance of Stokes' Mnemonics for the Multipliers, I do not think I shall ever forget. Can he and will he extend it by some remarks on the cylinder and cone? I, and perhaps others, find great difficulty in remembering formula expressed in powers of a and r.-J. H. M. [4969.]-PLUMMER BLOCK.-Where can I get details of the best and most scientific form of plummer block or pedestal for shafting? A thoroughly well considered drawing, with dimensions given for various sizes, based on the diameter of the nick, would be a great boon to younger subscribers.-G. W. T. spondents inform me of the process of printing or copying [4970.]-PRINTING ON JEAN.-Can some mats: it is a bouquet of maiden's hair and other fern of fern leaves, upon fine jean, made use of for toilette leaves, apparently laid on the jean, and other parts made darker all over, except where the leaves are; and even they are shaded in different parts, and appear as if they were at the back of one another. They are dark in the centre and the ground-work gradually verges to a light shade at the extremities.-A BOTANIST. [4971.]-PHOTOGRAPHY.-Thanks to "Operator' for his kind intimation to supply information where needed. I wish to enlarge an ordinary carte to a size, say a double page of the ENGLISH MECHANIC, by sunlight, but as this medium will become scarcer, perhaps "Operator would not object to give us the process, both by sunlight and artificial light too. If he would also give us the process for copying prints for exhibition in the magic-lantern, I should be glad.-LEX. corre [4972.]--THE GEOLOGY OF NORTHAMPTON.--Could some of your geological readers kindly inform me how I could best obtain a good knowledge of the geology of Northamptonshire? I am a student of this interesting science, and find difficulty in ascertaining to what particular series of rocks certain fossils of my collecting from the neighbouring quarries belong. For instance, I find in one parish specimens of Rhynchonella, Terebratula, Modiola, Ostren, Belemnite, Lizards, Ainmonites, teristic of any particular series of the Oolite, and if so Pecten, &c., and wish to know if any of these are characto which-for this formation has as many as fifteen divisions by geologists. I am pretty well satisfied that all my specimens are from the Oolite, but can't satisfy myself as to which bed. I wish likewise to know if the various beds of ore worked in the county at different places are the same geologically; and likewise to learn the particulars of the strata passed through in the Kingsthorpe shaft when sunk in search of coal. Are there any books or maps published with reference to the subject ?-GEOLOGIST. [4973.]-COLOURING PI ANS.--Will any one of your art correspondents be kind enough to instruct me as folows:-In the business I follow I have to make plans or maps of my work, consequently I make use of watercolour paints. Now, so far as I am equipped in the work (for I am self-taught, but am yet a learner) I find a great difficulty in laying on my colouring matter so as with a degree of success I have to give a pale tint. I find to give a uniformly coloured surface, and when I do so it expedient at times to colour highly, or thickly-here comes my difficulty of colouring uniformly. Also I have seen water-colour paints exhibit a fine smooth and polished surface. How is this accomplished? If by mixed with the paint, say what? Also be kind enough varnish, say what kind, and price? if something is to inform me how to choose paper best suited for this kind of work.-YOUNG YORKSHIRE READER. [4794.]-GLOBES.-If any of the good-hearted contristructions how to construct the body of a globe, viz.: What it is made of, and how put together; where the paper covering is to be obtained, and for what diameters varnish used; they would very greatly oblige one who it is made, and the probable cost; also the sort of has received much information from its valuable pages. butors to the ENGLISH MECHANIC will write out full in -S. H. [4975.]-MODELLING.-I have unsuccessfully tried pipe-clay, can any friend kindly inform me what is the best material to use ?-FOLIAGE. [4976.]-SCRATCHES ON PLATE GLASS.-Can any subscriber tell me if I can remove scratches from plate glass, and how ?-W. J. RAYLAND. [4977.]-LUBRICANT FOR BELLOWS ACTION.Can any organ correspondent inform me whether black lead or grease ought to be used as a lubricant for bellows action, swell pedal, &c. ?-W. J. RAYLAND. [4978.]-ENAMEL.-Can any of your readers inform me of an enamel that will dry without being heated in an oven, as I want a recipe for something of this sort, that when set it appears white and hard, like the white enamel used for earthenware ?-ARDASIER. [4979.]-ACHROMATIC CONDENSER.-May I ask one of the gentlemen who write on the microscope if there is any inexpensive way of adapting a fin. French object-glass as an achromatic condenser?-R. E. G. [4980.]-LATHE.-I have a 26 in. driving wheel, with three motions each, of an inch each less, and I have two wheels for back centre,with 40 teeth, pitch,--would some one tell me what size, or what number of teeth, the other two wheels should have for back-gearing, and what size the smallest groove should be on the cone to get the right speed to turn iron ?-GEORGE BELL. [4981.] with much interest Mr. J. W. Baskerville's remarks on feed-water heaters, and the economy to be derived from their use. quite impossible to save as much in fuel As his calculations clearly show, it is as Mr. Crompton asserts, viz.25 per cent., by the aid of feed-water heated by 55lb. of steam, but he does not say whether a nearer approach to this estimate may not perhaps be made by using steam of a lower pressure, say 30lb. Is this possible or not? If Mr. Baskerville would kindly reply, and illustrate his remarks, if possible, by a table, showing the temperatures of steam at varying pressures, he would greatly oblige-VERTUMNUS. FEED-WATER HEATERS.-I have read [4982.]-HEAVY FLUID-I am in want of a Anid whose specific gravity is greater than that of water, and if much less than that of mercury it would answer my Is object, if, like mercury, it would not mix with water. it possible to make an amalgam with mercury, that would be volatile and the alloy not liable to separate ?-H. HINDLE [4983.]-PIANO. A Collard cabinet piano, come recently into my possession, stands in tune very badly. It will fall a whole tone in three or four weeks. Can any means be used to obviate the constant tuning thereby entailed? The green silk front is rather faded. Could it be dyed without taking it off its frame, and how? I should be obliged if "W. T.," or any of our musical readers would reply early.-PENTA. [4984.]-FURNACE.-Will any reader inform me how make a small, cheap, and portable gas or spirit furnace, suitable for melting small quantities of iron or brass, also cost of the same ?-H. F. O. H. [4985.]-LIFTING PUMP.-We wish to force water into a boiler with 401b. pressure, with the same pump is 1in. wrought-iron. Will anything more than an that lifts it out of a well 21ft. deep. The pipe from well from pump to boiler ?-APPRENTICE. ordinary lifting pump be required, and what size pipe spondent inform an amateur how to take spots out of [4986.]-SPOTS ON MAHOGANY.-Can any correpolished mahogany supposed to have been caused with water? The spots are white.-D. A. [4987.]-SPUR-WHEEL TEETH.-Would some exout spur-wheel teeth, describing the epicycloidal curve; perienced pattern maker show the best mode of setting and the making of template and gauges? Name a good book on the subject. Will one of our mathematicians recommend to me a work on mathematics suitable for a practical engineer? Is Olinthus Gregory's the best?PRACTICAL ENGINEer. battery described by you on page 624, attributable to Dr. [4988.]-AMALGAMATED ZINC.-The little galvanic Golding Bird, will probably be very useful for general purposes, and pleases me much. If any courteous correcerning the "amalgamated zinc," its composition and spondent will kindly give me a little information conhow best to prepare the cylinder, I will endeavour to manufacture a battery.-W. R. [4989.]-COATING IRON PIPES.-Can any of our numerous readers tell me the ingredients of Dr. Augus Smith's preparation for coating iron water-pipes?-W. J. [4990.]-FEED-WATER HEATERS.-I would like to ask Jas. Baskerville (in reference to his letter on the popular delusions concerning water heaters) a few questions. First, how is it that (the melting point of lead being about 600) my lead plug on the furnace crown, and the sheet lead seating under the safety valve of my boiler does not melt away with steam at 40lb. pressure, or 1,200 of heat as he tells us we have, one being under the water, and the other exposed to the full heat of the steam, that is at about the hottest place on the boiler? Next, how does he make the average temperature of feed-water 40? I find my well at 28ft. deep is 52, and a pond just by (with a spring at the bottom) is 67° at the present time. I find Regnault gives 287 of heat for 401b. pressure, and Ure about the same.-ONE EYE. [4991.] - BITTER ALE. Would some courteous correspondents kindly state how bitter ale is made, the process it goes through, and the ingredients of which it is composed ?—T. O'BRIEN. give me directions as [4992.]-HOME GROWN TOBACCO.-Will some one method of preparing the above, for cigars or shag?— to the time of cutting, and KNOWLEDGE IS POWER. [4993.]-CRACKING OF HORSES' HOOFS.-Can any correspondent inform me what I can do to prevent a horse's hoofs from cracking; the horse is constantly on the road ?-L. S. [4994.]-GALVANIC BATTERY.-Would "Sigma" kindly answer me this question? I am constructing a medical coil of 2lb. No. 16 copper wire. Now instead of attaching a power to every helix, which is the common mode of proceeding, involving a deal of connections and extra care and trouble, could I not regulate the power of the coil by means of the battery, and employ only one mate, or, as you call it, bottle battery, with a regulating unbroken winding wire? The battery I use is a bichropiece of zinc.-W. A. [4995.]-DYEING GOLD COLOUR.-I want to produce a bright gold colour on manufactured dyed material, such as silk, and mixed silk and cotton-for instance, ribbons or velvets. It must not rot or destroy the fabric; must be what is termed jast, and must not, as it is called, run. I do not require the mode of application, only the ingredients, with the proportions necessary to produce the desired effect.-T. S. L. [4996.]-THE SATELLITES OF URANUS.-I believe I may conclude, from Mr. Proctor's remarks, that the apparent orbits and direction of motion are correctly shown on p. 522. If so, I am afraid I have not rightly apprehended Mr. Lassell's data. Would any other contributor, equally obliging but with more leisure, than Mr. Proctor, look into the matter? Some of Mr. Lassell's observations are recorded in "Monthly Notices" Vol. VIII., p. 44; XII., p. 152; XIII., p. 148; Mr. Dawes's paper is in Vol. VIII.-ETUDIANT. [4997.]-ANALYSES OF MINERALS.-I have a great desire to learn to make analyses of minerals, such as ironstone, coal, and coke. I don't know anything about chemistry to begin with, and only have one leisure hour per day to devote to my study. Will Mr. G. E. Davis be kind enough to assist me by stating how I am to proceed with my study? What books and apparatus I shall require, and the cost of same? By so doing, he will extremely oblige-A COLLIER LAD. [4998.]-SCHOONER YACHT.-I want to build a model schooner yatch. Would any correspondent be kind enough to give me particulars as to form of ribs from stem to stern and other lines?-SCHOONner. [4999.]-OPERA-GLASSESWITH SIX AND TWELVE LENSES.-I often see these advertised, but am at a loss to understand on what principle they are constructed, considering the wide difference between the focal length of a small pocket telescope and the ordinary opera-glass of two lenses only. I should be glad to know their magnifying power? What is the shape of the lenses, and how is it that when so many are used all the light is not absorbed, and how are they made effective in so small a space ?-AMATEUR. [5000.]-SMOKED MARBLE.-Can any one inform me of a material that will erase the black or cloudy |