the link is derived from the excentrics through the rods, and from them alone; and no matter what part of the link, be it the end or be it the middle, is in gear with the valve-spindle, the nature and amount of its vibration is ever the same; and its position with regard to the valve-spindle has about as much to do with modifying that motion as the handle of the stoker's shovel has. Fig. 2 shows the forward gear end of the link in gear with the valve-spindle, and the reversing lever (not shown) in the end notch of the rack. In this position all the movements, and attitudes, and angles made by the link during a revolution are of course identical with the middle gear position; it is impossible they could differ in the slightest degree; and all that Mr. Harrison says about the centre of motion being 2in. higher up or lower down, and about the disengaged rod receiving all the angles, and about "that end of the link having almost double the vibration," is pure unmitigated nonsense, without a shadow of foundation in reality or fact, and his three diagrams are on a par with the text they are intended to illustrate. I have already said that in Figs. 1 and 2 the centres of the excentrics are placed diametrically opposite each other, and without lineal advance, and the object of placing them so has been explained-viz., to illustrate the impossibility of constructing the ordinary link motion with a motionless centre; but excentrics set in this way are not suitable for working a slide-valve, because all slide-valves have more or less of lap and lead, and, therefore, require the excentrics to be set with more or less of lineal advance. I have also to remark that the excentric rods shown in Figs. 1 and 2 are unusually short as compared with the length of the link and the throw of the excentrics; and I have purposely made them so in order to exhibit in a conspicuous manner and on a large scale the influence which the crossing of the rods has upon the movements of the link, for short rods are more influential in that way than long ones, other dimensions remaining unaltered. JAMES BASKERVILLE. "' in [242] SIR,-Mr. Harrison commences his letter very well, by apologizing to Mr. Wheatley for his unpolite reply to that gentleman's letter. He also confesses that he knows very little about the link motion. Such a confession on his part I think quite unnecessary. But he spoils all by the "would-be satirical way which he alludes to my letter. Allow me to correct his assertion that my diagram (Fig. 2, page 425) is a copy of Mr. Baskerville's; the dimensions are taken from the working drawings of an engine now running on one of the chief railv ays in Ireland. Now, sir, if Mr. Harrison will not agree with either Mr. Baskerville or myself that the link does not swing on a centre, I hope he will accept the authority of D. K. Clarke's "Railway Machinery." In that work he will find a series of diagrams showing the curve described by the working point of the link, in full, backward, middle, or full forward gear, whether hung from the centre or bottom end. Now, one of the defects of the curved link is, that if the motion is set to work with in. lead in mid-gear, it will become 3-16ths or mere when working in full back or forward gear; this difference in lead increases as the rods are shortened, so that the general practice is, in designing motions for tank engines or locomotives in which the motion must be short, to substitute for the lifting link the stationary reversed link with the reversing gear attached to the pulling rod, which works up and down in the link: a constant lead is claimed for this motion. Now, as discussions in your valuable journal should be conducted in all good nature, allow me to say that if Mr. H. would wish for a set of diagrams I would be V most happy to send him a set showing the position of the link in all parts of the stroke. If he will not accept my authority, all I can do is to refer him to the work above. In the mean time, I think if Mr. H. will examine the diagram (Fig. 1, page 425), he will come to the conclusion that the link moves to a small extent along the motion line, on account of the rods drawing the link, top and bottom, towards the excentrics where they cross. This occurs even when the excentrics are placed diametrically opposite. But engineers require the link to open the ports even when in middle gear, and for that purpose they give the excentrics an advance of 1-16in. which with lin. lap on valve, 5 in. travel of excentric, and, of course, all other dimensions suitable, would open the ports in. on each side. As for the letter of "R. H. M.," in which he states that with the excentrics in the position shown on page 425 the rods ought to be crossed, I really do not know what to say about it. Either I know nothing at all about the link motion, or else "R. H. M." has ideas about it totally at variance with all known A HANDY TENT FOR PHOTOGRAPHIC [248] SIR,-I send you a sketch of a handy tent for the benefit of any of your photographical readers who may be contemplating the practice of their art during the holidays. It is taken from the Philadelphia Photographer. Drive a stake in the ground so that it will be about 3ft. high; now take a common umbrella, tie the handle firmly to the stake, then place a double sheet of black and yellow calico over it, leaving a small hole in pellets, &c. A pellet in a ring at the head m the horse. The device is partly surromed br a beaded circle. In very fine preservation G. size, in. by in.; weight, 95 grains. On rim of the obverse are marks, looking like a legend. The type of this coin is the first class of Evans ("Coins of the Ancient B plate B, No. 8), and is very like those in ("Annals of the Coinage, &c.," plate I., No and 4.) This is the first ancient British coin that is bu have been found at Brighton; a copper one of ferent type is said to have been found there Evans, p. 206, plate IV., No. 12), but Mr. Evan not satisfied of the fact. I purchased my ein et man who found it, and myself know the erst spot. HENRY W. HENFREY, MNS.. EMIGRATION: WHERE TO GO-WHO SLI GO-HOW TO GO-WHEN TO G [244] SIR,-If Emigration is still ente space for discussion in your columns, Ian He to say a few practical words on the sal I would divide my observations into four p 1st. Who should go.-I would advise in p have not had some experience as practica who cannot form a society in which the ob the land shall be the principal object, and t individual shall bring an experience in s useful on a farm; this would in no way ente mechanics as smiths, carpenters, wheelwrigs I am of opinion that a practical farmer, a mi carpenter emigrating together (with their famika.s if they have grown-up sons and daughters so muda better) would be sure to succeed if they go to the place. 2nd. Where to go.-To a British colony, or to United States, for practically I think the choice is t limited, as emigration to foreign countries that i say, to non-English speaking countries-for the re nary British emigrant is the height of folly. Th British colonies may be divided into the Australian South African, and British North American. The first and second division are difficult of access on account of the distance and consequent expense of passage, and so for the present I will pass them over, and take Canada as the colony to be compared with the States. It has great advantages. It is prosperous, fertile, rich, well-settled; and, moreover, English, Irish, and above all, Scotch, will find themselves "at home" there. Land is to be had cheap, and the intending purchaser or tenant may rely upon being justly dealt with, both by the Dominion Government and the Canada Company, in whatever engagements they may mutually enter into. They may also be certain that erke cleared and cropped, the land will ultimately amply r pay their labour and outlay; but, oh! the weary ward of clearing a Canadian "concession" (I write andr the supposition that the emigrant has not the ca to purchase or rent a cleared or partially cleared farm but that he simply brings his labour and b money with him). The felling of the forest, and the grubbing up and splitting the stumps is heartening work to those who look upon may so much land to be tilled; whereas, all cleared land is a forest to be reclaimed; adds to farmer has to make and maintain his own road, as his concession extends; and, lastly, all th allotted (Government) lands are far in the back far from towns, villages, or railroads. In this day tion I exaggerate nothing, nor do I suppress a that could brighten the picture. The climate & treme-in summer dreadfully hot, and in severely cold-but, in justice to the winter climat must be admitted it is not disagreeable or unheal It is dry, bracing, and cheering, so that to sum aple not advise emigration to Canada for the class of pr sons I am advising to leave England; but I do t strongly advise such to go to the Western and North Western States of America, and there settle on the prairie lands, offered now on most favourable term most of the great railroad companies. Of these Su and of their advantages and capabilities, enough b been published for every one to have an idea of w they are; but I know how suspicious all EnglishBritish emigrants, are of all American land p spectuses, no matter by whom issued. Now I am r going to select any of the many railroad compan who offer land to settlers, but I know that with hard an exception they are all genuine, and it would be h to advise intending settlers in their selection. 3rd. How to prepare for going, and how to go.-I woul advise (always supposing a society formed) that the farmer should go first and select the land; th on most of the railways he can do by going to the agency of the company at New York, and there seeing on the map the disposable lands, and then before lay ing out one penny, or rendering himself liable in ar way for anything, he can see the lands himself and make his bargain; then, if he is satisfied, let him send passage tickets from America to his friends at home. by one of the great steam lines from Liverpool, Lon don, or the Clyde. He will find this the best way; as if he has English gold or bank notes, he will enjoy the advantage of the premium on gold which exists now in America, and is likely to continue. I do not specify any particular line of steamers, but I most em phatically warn every one against any sailing vessel whatever. 4th. When to go.-Preferably the early spring (say April, and I should say on no account go after the end of May, as later the heat is terrific, and makes a steerage passage, even the best appointed steamer, a perfect misery. At any time on the passage is a discomfort, but in an always crowded steerage, with the thermometer at 80° to 90°, and too little ventilation, the state of things is dreadful. I have had official experience of it. D. G. IGNITION BY ELECTRICITY. [249] SIR,-I saw an enquiry a short time since in our paper about igniting gas by electricity. Perhaps the enclosed cutting from the American Technologist will afford some of the information "W. H. B." asked for:-The idea of using electricity to ignite inflammable substances or explosive compounds is not Lightning, which is nothing but an electric discharge on a large scale, produced in nature's laboratory, has effected this from time immemorial. The ignition of alcohol, ether, gunpowder, &c., by the electric spark, is one of the oldest experiments in this branch of physics, and during the last one hundred years has formed one of the standard experiments in the philosophical lecture-room. Electricity produced by friction was proposed and practically applied to the lighting of gas; the small amount developed when the feet are rubbed on the carpet in a very dry room is often sufficient to charge the person, so that by touching the gas jet a small spark will appear, which will ignite the gas readily if the latter be turned on to a proper degree. Many devices have been contrived for the development of this made in Groningen, Holland, with a glass disc, the frictional electricity. Thirty years ago machines were whole being enclosed in a glass case, nearly hermetically closed, and provided with chloride of calcium or other hydroscopic substance, which would absorb all moisture, and thus keep it dry, so as to ensure the obtaining of a spark in all states of the weather. Batchelder, of New York, patented a small friction machine, which was hidden in the ornamental globe attached to the lower central part of a chandelier. When the gas was turned on, and a knob which rotated in an inside disc or vulcanite three inches in diameter was turned, a spark was conducted to the burners and the gas was ignited. Vance, of New York, invented a gas lighter in which a similar machine was placed above the handle, and turned by means of a small handle. The insulated metallic rod attached to the lighter was thus charged, and when brought against the gas burner it emitted a spark, thus lighting the gas. Cornelius, of Philadelphia, patented a small cup, lined inside with silk, and closed with a stopper of vulcanite, the whole being attached to the gas bracket. When the gas was turned on and the vulcanite stopper lifted out of the cup, friction enough was produced to develope an electric spark, which was conducted to the tip of the burner by means of a small insulated metallic chain. In 1860 Van der Weyde, of New York, presented to the Smithsonian Institution, at Washington, a simple syringe of vulcanite, which, by sliding the piston along the interior of its cylinder, produces electricity enough to do the same thing. It was, in fact, a small and very convenient instrument for developing small amounts of electricity for experimental purposes. In 1863 Wesolewski patented a very neat and very small frictional machine of vulcanite, in which a lamp 11 1 320 Hence-I ing to the careful examination of some "bitter I found no trace of acetic acid by optical and saw some isolated cells of Torula and, horri choose the fraction of D E, to reduce error on the late, a goodly number of bacteria and vibrion appeared to be in the liveliest condition. T 4th, &c., the spectacle was most edifying and. containing bisulphide of carbon was lit by a spark, the longer and quicker, becoming at least, whole throughout all possible arcs. Mr. Drach's very curious discoveries were not proposed, I conceive, as geometrical approximations, but as arithmetical abreviations of the process of multiplying or dividing by 3.14159265, &c., for which they are surely most remarkable, and up to these first nine or twelve figures, very useful. In fact, he represents the above nine by a combination of factors that contain but five significant figures; thus (3-3008007) × 1:05. Pushing the principle further, he shows how the effect of these twelve, 3.14159265359, may be got from the same 5, and two more, namely, adding (3-'008007) × 00000000012. This is perhaps the limit of utility; but if exactness to 16 decimals (that is, to a thousandth of = W. R. RECTIFYING THE CIRCLE APPROXIMATELY, [250] SIR,-There must be many ways, equally simple and much more exact than any lately described, for obtaining with ruler and compasses alone the approximate length of a given entire circumference, or aliquot parts thereof. Thus, Hutton erects at the ends of a diameter two perpendiculars, one = 3 radii, the other tan. 30, and the line joining their tops is within a hundred-thousandth part nearly the semicircumference. But I conceive that the real problem, to be usefully solved, must apply to every arc. whether commensurable with the circumference or not; and comprises three cases. 1. To rectify particularly any given arc. 2. To lay off on a given circle an are practically of a given length; and 3, to construct an are subtending a given angle, and practically of a given length. For the first of these I venture to doubt if the following has been, or will soon be surpassed. It is probably new, being derived, bat considerably improved, from two invented and published as new by Professor Rankine in 1867. a hairbreadth in the circumference of the earth) should ever be needed, he obtains it by one figure more, subtracting from the last factor 0000000000002. The extensions he has contrived beyond this, to 18 and to 31 decimals, are wonderfully curious, and that is all; but we must remember the arithmetical processes are abridged in exact proportion to this reduction of the number of significant figures, or rather of figures above unity. E. L. G. P. S. As far as the above number is quoted at all, it should be correctly 3.1415926535597932384. Though the 17th and 18th places might be 01 without greatly affecting society, the sixth must not be a 1, as twice printed in Mr. Proctor's letter. [251] THE SATELLITES OF URANUS. SIR, I have endeavoured to comprehend the movements of these bodies as described in astronomical books, but I cannot succeed in making the data given by Sir W. Herschel agree with certain statements of other excellent observers of these distant bodies. Sir W. Herschel in 1798-the epoch of the ascending node in long. 165 -found the plane of their orbits to lie 81 south preceding, and 79 north following. These, in our modern method, would be Pos. = 189 and 11; this would make the inclination to the ecliptic abont 80 on the W., and 100 on the E. side respectively. He had previously found the motions to be retrograde. Now when half a revolution of Uranus had been performed-say in 1840-the ecliptic would be similarly inclined to the circle of declination on the other side, so that near the descending node the plane of the orbits would be inclined about 10° to the meridian, in Pos. = 170 and 350. In figs. 1 and 2 the apparent orbits are E FIG. I Given the arc A B, whose centre is at C. To lay off on the tangent A G its approximate length. Bisect the arc, and bisect again the half next A, by the secant CD, meeting the tangent at D. Draw the chord, B A, and produce it to E, so that A E = half of B A. Join E D, and make D F = two elevenths of D E. (This division is only necessary in the case of very large arcs, approaching a semicircle, or at least a quadrant. For any under an octant there will be no sensible difference if D F be as little as an eighth, or as great as a quarter of D E). From F, with radius F B strike an arc B G, which will cut from A G the required length. The error is positive, or A G longer than the arc, when this is a quadrant or anything less; but at some arc I have not determined, between 90 and 180°, the error vanishes; and for arcs approaching a semicirele this is reversed, or the line A G too short, the defect, however, barely reaching a ten-thousandth in the extreme case of rectifying a whole semicircle by one operation. By distinct calculations I find 1798 184-0 W W shown as projected on the meridian, the strong lines denoting the plane of the orbits, the thin lines the meridian and circle of declination, and the dotted lines the ecliptic. The arrows indicate the direction of the motion of the satellites (as I suppose) in the half of their orbits nearest the earth at the nodes. A telescopic view is, of course, obtained by an upside-down view of the figures. Now, in 1851-2-when the apparent inclination was on the same side of the meridian, as in fig. 2-Mr. Lassell observed the satellites at their greatest elongations to be in Pos. 823 south preceding, and north following, say 1871 and 71°. How does this agree with probably never reaching 30,000; and then so decreases with further increase of curve that the quadrant is rectified more truly than an octant. In still more curved arcs it decreases to nothing, passes to the opposite side, and thus barely reaches a sensible amount for any arc, even up to a semicircle. For ares below 60° the errors would be even less if we made D F DE, and the positive maximum be less; but as it MICROSCOPIC EXAMINATION OF ALE. would occur at a lower are the change of sign would [252] SIR, It may interest "John Barleycorn" to be at a point below 90°, and the negative error increase hear that I devoted a few spare minutes the other even = CALLAUD GALVANIC BATTERI [253] SAR,-There would seem to be aflost your readers an error as to the name of thr of the so-called "gravitation" galvanic battery. "What is in a name ?" will not hold in t for the mistake has already caused a misco the mind of at least one correspondent. The should be Callaud not Calland. In the year 19thland, of Nantes, called the attention of t Academy to his new battery, in which the pr was absent, and the liquids were kept from "superposition." Verité, of Beauvais, te m the wonderful astronomical clock of Best dral, hit upon the same idea some time l Both these inventors requiring electrial clock-work motion, had not to trouble the a the great objection to this battery-that su not be shaken; otherwise, it is stronger, and uses less sulphate of copper than Dan [254] SIR,-Your correspondents "Bernare a "Oceola" are, I think, in error in regard to tra ments about the non-existence of a mammoth sh in Great Britain. There is a perfect skeleta da mammoth in the Natural History Department da British Museum, and several parts of another skelka together with a specimen of the hair, which was feat embedded in ice. I would advise "Bernardin" to the the British Museum (if he has not already done so, i I have no doubt he will be as much pleased with on English specimen as with any to be seen on the Cant AN ASSOCIATE OF KING'S COLLEGE, LONDON. nent. THE FIELD BOILER [255] SIR,-Permit me to correct a statement in your last issue regarding the "Fisid" boiler, which is likely to mislead. After having stated that upwards of 60,000 Field" tubes are now at work in this country, you say:-"They are not likely, however, to be generally adopted for factory and other uses, wher more liability and neglect exists." In answer to t statement, will you allow me to state that upwarded 370 Field" boilers have been made up to da a this country, and with few exceptions are all empl for factory purposes? The number of tube and boilers mentioned above do not include those Messrs. Merryweather & Sons for their w steam fire engines, as they have the set employing these boilers for that partica 273 In addition to this I may mention that pat number of "Field " boilers are made od amounting to about ten times the number made to la England, one firm alone having turned as malj al 150 boilers a year during the last few years I trust that this statement may satisfy yo your numerous readers that the Field Müre safe and reliable for all stationary and purposes as any other boiler. LEWIS ÚL THE INDUCTORIUM.-IRON IN BATTERIES [256] SIR,-Your readers owe thanks to "Inim torium" for his description, p. 472, even theagh mode of construction described be well known. Ik he would find it less trouble to pass the wire tar the melted paraffin while winding. It is very ea done by fitting a cover to the vessel, in which yog shaped holes or rollers are provided at extreme opp sides; and also a frame carrying a roller, which to the bottom of the vessel, which is then placed s away as is convenient over a regulated gas burner. would find it an improvement, also, to increase diameter of his dises gradually from the ends, the s of the coil being brought to that of the curves of to magnetic force generated by the primary. In reply to his question, I have not particula measured the vacuum my Tate's pump gives; I c know that it has answered the purposes I have used. for better than other forms. In reply to Mr. Preston, p. 497, I think he is corre as I have no doubt that the inner turns of the secouter are by far the most effective; as the onter on d crease in length, their resistance is increased, ault force is used up in overcoming it, and as the force it. diminishes, also, the useful effect is much lowered; the real objection to great length is, of course, the increase primary and resistance to the battery, and, therefor greater battery power is required. Will Mr. Jarman, p. 447, say wherever he got inv great curiosity, as it is about ten times the usual pr from containing 65 per cent. carbon, as it would be portion? The figures of cost given by " Omega," p. 494, as con paring the Bunsen and Slater's iron cell, differ co siderably from my results, but I am unable to compar them, because the conditions are unknown in his ess and so much depends on the actual strength of t.. acid, and accurate results can only be obtained working from the equivalents of the materials. rather suspect "Omega's" nitric acid was weak, # this alone can explain the difference in the amount cl work if the measure capacity of the cells was the same. Of course, independent of local action, zine will consame faster than iron, as its equivalent is 32-6 against 28. Another matter is that the comparison is not a fair one for another reason-viz., that equal numbers of the rells are used; now 24 cells are very greatly in excess of the number which can be advantageously used to decompose water, or, more correctly, dilute acid; and as the electro-motive force of the Bunsen is the highest, this tells most against that battery. With "Omega's" other remarks I entirely agree; and I may add that the electro-magnetic engine for use with which the battery was mainly devised is a very excellent and powerful form. SIGMA. AN "ENGLISH MECHANIC" SOCIETY FOR LONDON," Tometer" says:-" I am much surprised and grieved to find that there are so little hopes of a Mechanics' Mutual Improvement Society being established here in London. I should have thought there must be subscribers enough to form a hundred societies such as that proposed by a correspondent a few months I believe if a meeting were held there would be plenty of attendants, but very few care to write, as they seem all to think there will be plenty of others write without me,' and, therefore, none write; so the thing drops. I really do hope something will be done in reference to this important subject, and, I should say, the sooner the better." ASTRONOMICAL NOTES.-I trust the "Fellow of the Royal Astronomical Society" will not be moved by Mr. Frith, or any one else, to falter in giving us his kind and valued "Notes." Let him be assured that there are lots of quiet-going fellows like myself, who, though they may not express it as I do now, enjoy those "Notes" particularly, and scan them always with keen appreciation.-GIMEL. MECHANICAL MOVEMENTS.-This part of our paper is very interesting, and I have no doubt when it is completed, it will go into the form of a book. True, the ENGLISH MECHANIC itself is a convenient "book," size (not too big), but still the "Mechanical Move ments" would form a nice neat volume; and some of the more attractive items could be expanded by a system of notes, copious and explanatory, and a full index would (as ever) make the book complete. GIMEL. MIRAGE.-Mr. W. L. Carpenter, writing to Nature, mentions a mirage which occurred on the coast of Portugal, on the same day as the remarkable one seen in the Firth of Forth, July 22:-"A reference to my journal shows me that on the same day we were dredging on the Portuguese coast, within sight of the Ferilhoc and Berlinga Islands, about forty miles north of Lisbon. The bearings of these islands and their exact distance, calculated by the aid of the known height of the lighthouse, gave us, of course, an exact position, which our dead reckoning' also confirmed. Several solar observations, both for latitude and longitude, were taken by two of the officers during the day, both of whom always arrived at the same result, but this was so widely different from our position as previously determined by two other methods, that we were forced to the conclusion that there was a very false horizon. It was the only instance of the kind during the inouth I was at sea." AN IMPROVEMENT IN GALVANIC BATTERIES.— Mr. W. Poole Levison, of Cambridge, Mass., in a letter to the Journal of the Franklin Institute, says: "In the spring of 1869, while making use of a small bichromate of potash battery, I discovered that the addition of nitric acid to the mixture of potassic bichromate and sulphuric acid, contained in its porous cups, conferred upon it the virtue of steadiness, without involving the evolution of annoying fumes. For over two months, during last summer, I had in almost constant action a combination of twenty-three large Bunsen cells charged with dilute sulphuric acid and the triple mixture mentioned, and set up' openly upon the floor of my room. Not only did I work about it with perfect comfort, but left choice brass instruments in its immediate neighbourhood with impunity. Its energy never fluctuated, and after remaining for some time steady, declined, precisely as if the electro-negative plates were bathed in nitric acid only. To a cooled mixture of potassic bichromate solution and sulphuric acid (perhaps preferably in atomic proportions) add nitric acid. The proportion of nitric acid may be greatly varied, as its office is merely to transfer oxygen." corre in the least. The prints at this stage have rather a REPLIES TO QUERIES. **IN their answers, Correspondents are respectfully requested to mention in each instance the title and number of the query asked. [3983.]-ENGINE INDICATING.-As nobody else appears to answer this query I will try, though only a learner myself. Before you begin to adjust the indicator, see that it is perfectly clean, free from grit, and well oiled with the best oil. Next fix your indicator to the taps in the ends of the cylinder if possible, as the sides are objectionable; next gear your band to some convenient part of the engine to get the required stroke for the indicator. If a beam engine, the radius bar; if a horizontal, you must gear a lever from the crosshend to the roof of the engine-house; then fix your band towards the tap, so as to get about a 5in. stroke, more or less, to suit your indicator; then carry your band towards the cylinder on small pulleys, over the indicator; then couple your band, but be confident your band is long enough at first, as you can shorten it with a running loop at pleasure. You must be careful and see that your stroke is not too long, so as to cause the indicator barrel to stop at each end, in which case it would produce a defective figure. This done, wrap your paper round the barrel, sharpen your pencil to a very fine point and let it touch the paper as lightly as possible, but before you take the figure see that your indicator is in working order by letting it work a few strokes. Should the diagram, when taken, resemble the above, [4011.]-PRICKING ORGAN BARRELS.-" C. W. A." reach London (not to say Ipswich), the aggregate thicknosses have summed up to about ten miles, and as the most rapidly shoaling parts of present sea-bottoms, the Gulf receiving a foot of sediment per annum, "Veritas" may of Venice, or the mouths of great tropical rivers, are not reckon a minimum of time for the deposition of these ten miles, but only a minimum. The fished-up cable showed that the Atlantic is not depositing half an inch of its chalky mud per annum. Certain sandstones, that there is much reason to believe are the quickest deposited strata, show laminations about forty in an inch, that were most probably each the effect of a twelve hours' tide. These are about all the data that geo-chronology has to theorize on.-E. L. G. [4283.] WARPED CABINET LID. I fear that "J.B." (the second) will find that even if he succeeds in straightening his warped cabinet lid by "Cabinet Maker's" method it will warp again. Because as the part which he swells by damp in the manner proposed gets dry it will naturally shrink as before, and so twist as before. In order to prevent this, therefore, I would advise him if and when he gets it straight by the mode prescribed, which would be helped by a few weights, to have grooves made across the grain of the back of the lid to the depth of half its thickness, and in width and number in proportion to the size of the lid, and if into these he fits with glue and screws, slips of perfectly dry wood, I think he will find his work likely to stand, which otherwise I doubt.—J. B. [4361.]-METHYLATED SPIRIT.-This composition is not allowed to be used in the preparation of any medicine to be taken internally-i. e. to be drunk; and several parties have been heavily fined for selling it flavoured with various essential oils so as to render it potable. It is prepared by mixing nine parts grain spirits, generally from 60 to 65 o.p., with one part wood naphtha. Both its preparation and sale are hampered with stringent fiscal regulations. T. L. H." has misinformed the querist in this case. I have had less or more to do with methylated spirit ever since the act came in force-now thirteen years since.-A REVENUE OFFICER. [4380.] - - COLZA OIL.-" Bernardin" is mistaken when he says that colza oil is the same as rape oil. Colza is extracted from the seeds of Brassica oleracea or B. campestris oleifera, which yield from 86 to 40 per cent. of oil. Rape is obtained from the seeds of several kinds of Brassica, but principally of B. napus, which yields about 33 per cent. (sp. gr. 9128), and B. rape, which yields a smaller quantity, but of a specific gravity but as might be expected, it is extensively adulterated. of 9167. The specific gravity of the true colza is 9136; The mistake seems to have arisen from the Customs' returns classing all seed oils under the one head of "rape oil."-REBAF. of [4381.]-COURT PLASTER.-The following is the method described by Dr. Paris:-Black silk is to be strained and brushed over ten or twelve times with the following preparation:-Dissolve oz. of balsam benzoin in 6oz. of rectified spirits of wine, and in a separate vessel dissolve loz. of isingglass in as little water as possible. Strain each solution, pour together, and let the mixture rest, so that any undissolved parts may subside. When the liquid is cold, it forms a jelly, which is warmed and applied to the silk. When the silk coated with this mixture is quite dry, it should receive 4oz. of chian turpentine, to prevent its, cracking.-H. U. a coat of a solution of 6oz. of tincture of benzoin and 14882.] COPPER COINS.-The first coin named by "Hastings," (query 4382, page 454), is one of Faustina junr., empress of Rome; if the hair is put up something after the way of the present chignon; if not so, one of Faustima sen. The second coin is one of Hadrian or of Vespasian, emperor of Rome; if the head on the coin is very large it is one of the latter emperor, if not so, one of the former. They are called first or large brass.W. J. EGGLESTON, Dewsbury. [4383.] THREE COINS.-The first of the three coins described by S. S. Wright is a shilling of Elizabeth; the other two are 17th century tokens, struck in Antrim and London, by R. Young and J. Evin, during searcity of copper coins in the reign of Charles the First; none of them are worth much above sixpence over their intrinsic value.-W. J. EGGLESTON, Dewsbury. [4384.] COPPER COIN.-The copper coin of "W. B." engraved in query 4384, is probably a very early British or Gaulish coin, too early to be assigned to any ruler.W. J. EGGLESTON, Dewsbury. [4396.]-ELECTROS.-I am sorry "Faber" does not find my composition suit. I think he is sparing of the rotten stone, but remember I had failures in casting off metal of large diameter, as the stuff stuck in deep places. I do not remember having over much trouble in blackleading. I suppose there is blacklead and blacklead at the shops. The recipe was given me by a relative M.D., F.R.S., who got it from a professional, but so long ago (1812), that I do not remember quite all about its success or otherwise. I do recollect that I soon gave up electroI think the stuff is all the worse for remelting repeatedly, typing, and that some of my early casts were very good. at least my impression is that I was more successful at first than afterwards.-J. K. P. [4181.]-SUN-DIAL.-Whatever serves as a gnomon (let the dial face how it may) must have an edge or edges parallel with the earth's axis, that is, in this hemisphere leaning from south to north, and in London FIXING PHOTOGRAPHIC PRINTS.-A 384 from the vertical; moreover to be available throughspondent of the British Journal of Photography gives oat some hours, it must have its chief planes or sides the following method for fixing prints: Allow the facing due east and west. What "W. H. C." means, prints to get saturated in a solution of hyposulphite of therefore, by "supposing it to be placed exactly opposite soda, three ounces to the pint, and then well squeeze June 21st," namely, something like 40 north of east, I the point in the horizon where the sun first appears on them. This two or three times repeated is quite sufficient. The prints, after the first pressing, on being cannot tell. Any object will cast no shadow on the separated, immediately absorb a fresh supply of hypo. longest day at noon, if its north side reclines (in London) solution, as a sponge would do, which in its turn is elimi. 28 from the vertical, and its east and west do not overnated by pressure, carrying with it all the salts of silver: hang. The difference between "mean noon" (or twelve understand the last words of " Faber's" query (p. 455). [4397.]-SCREW TOOLS.-I am sorry not quite to and, as the pictures are such a short time (five or six o'clock) and apparent noon (or twelve o' sun) being on The words "and in top," appear a misprint. I suppose minutes) in the fixing solution, the tone is not lowered tion, because there are always two full minutes during the only way to make an inside screw tool from a that day only seventy seconds, will not affect the queswhich neither the east nor west face casts a shadow, this screw plate is to screw in a piece of steel, as in making a curious washed-out appearance, caused by the paper time being taken in their turning through the half degree/ tap, and then filing it thin by removing half the mateon drying, and are in the best possible condition for dials (and those of elegant forms) may easily be made to side, and all the thread, and more than that, say half of the sun's diameter. It is not generally known that rial from the top side and one-quarter more from unde a great saving of time, ditto of material, and an approxi- the year; and even to a second (except in a few days of tool. I have made an inside screw tool-viz., for a nut show clock time, exact to a quarter minute, throughout the breadth, from the back, to form an ordinary screw midwinter and fewer at midsummer) by having two 1ğin. diameter and fin. pitch, by flattening the end of a gnomons, used alternately for nearly half a year each. I steel bar gin. square, and drawing it out on one side just propose this problem to the ingenuity of some of your ends, and treating it as if it was a bar, with an outside like the "bit" of a key, and then centering it at both readers.-E. L. G. screw to be cut on it in the ordinary way, and it acted perfectly; really could not have been wished to be better. I may as well mention here, as many a workman (socalled) is not aware of it, that inside screw tools should be cut on a left-handed hob, and I have seen many from first-rate shops that were not done so. Also, I cannot see what "Faber" can want with screw tools so small as in., as the internal screws are so much more easily being semi-transparent; but they resume their brilliancy effectual washing. The advantages of this method aremaation to, if not perfect fixation." COAL FORMATION OF THE LOFODEN ISLANDS (NORWAY).-It appears that in the Island of Ando, one of the Lofoden group, a seam of coal has been discovered, which, in physical and other properties, bears a strong resemblance to the well-known boghead, but the thickness of the layer is irregular, and does not, as far as has been ascertained, exceed 20in. The diameter of this coal basin is about 2,800 metres. [4174.]-GEOLOGY.-Fossil plants from the coal measures grew at some period between half a million and three hundred million years ago, but which of these dates may be the nearer the truth no means exist of guessing. As the Cumberland strata dip in leaving that county, and are overlaid by others, these again by others, and those by others in succession, till, by the time we own. tapped, and I think any pitch whatever, up to about 30 or 35 to an inch, is kept in stock at Buck's, besides some finer ones, so that he can hardly be obliged to make his I do always make mine, having formerly been to the trouble (and very great, too) of making a set of hobs, and think nothing of making more if requisite, as I want them, but in those days aliquot pitches were not to be had at the shops.-J. K. P. [4399.]-INTERNAL GEARING.-I do not much approve of this plan in a general way, but to anyone intending to use it I would remark that the pinions should be as large as can be got in. Also, that internally geared wheels are commonly cut with a circular cutter in a frame specially made for the purpose, and are attached afterwards to the plate or rim of wheel that they belong to; of course it is difficult to make small ones this way. "G. W. A." has very nearly hit upon the best plan of making an internal wheel, when he says, "drill a series of sixty holes, &c.," but the chipping away neatly" is the difficult part. The way to get over this is to have a driller similar to mine figured November 12, last year, (and which you must have in order to slot drill any part of the teeth any way), mounted on a plate attached to the slide-rest, so as to be itself on the radius of the work, and slot drill the teeth by traversing to and fro, not on the line of the radius of work, as "G. W. A." proposes, but parallel to axis of lathe mandrel and lengthwise of the teeth. The tool referred to will work comfortably inside a wheel of 8in. diameter, and another I have intended for a different purpose would go inside a 4in. wheel. Of course a drill or grinder" made to the right shape is required. All this is not easy to describe without a drawing, and I cannot stop to make one now, but will give more particulars if called on to do so.-J. K. P. [4402.]-TELESCOPES.-Most telescopes have the screw parts cut so as to act as springs upon and retain the sliding tubes in any position. If "G. F.'s" telescope is so made a few slight blows with a haminer on the beak of an anvil, properly applied, will set these springs in and make them act more strongly; if, however, there are no such springs, and there are no means of cutting or making them, a ring of thin kid, fastened with shellac, and oiled, will give the required stiffness of draw.-J. B. [4409.]-FIXING IRON CRAMPS.-"J. W." will readily fix his cramps or other ironwork in stone by the use of Roman cement and bits of scrap-iron driven tightly with punches into the hole to jam the cramp. When the cement is set it is quite as strong as lead. J. B. [4410.]-TURNING SPHERES.-Q. Yorke advocates boxwood for chucks. I do not. Maple is much better wood for the purpose. Nearly all our chucks are made of the bottom ends of maple poles, and last for years. If "Young Amateur" finishes one side of his backgammon men before he cuts it off the cylinder he will have to chuck once instead of twice. "J. D. L." had better get a practical workman to turn his billiard balls, as I can assure him it is no easy job to turn a perfect sphere. He will only spoil his ivory.-WooD SPOON. [4412.]-WRITING INK.-Let “J. G. M." put two or three drops of carbolic acid into his inkstand, or about thirty to the pint of ink. The ink cannot then go mouldy, nor will this addition spoil the ink.-SPERO. [4412.]-WRITING INK.-" J. G. M.", will probably find that a small piece of camphor placed in his ink bottle will prevent the growth of the "mould" fungus.H. P. [4412.]-WRITING INK.-A few cloves (say two or three) put into an ordinary-sized inkstand will prevent it from going mouldy and also preserve its liquidity.WAHSROF. [4414.]—HEIGHT OF OBJECT.-If "Enquirer" will take two tubes and connect them in such a fashion as shall enable him to case them to form or any angle, he will provide himself with an instrument which will enable him to get approximately the height of any object, or width of any river. He may use it thus:Suppose he stands on the brink of a river, the width of which he wishes to know, let him measure on his side a given distance in paces right and left of some tree or building on the opposite bank. From each end of his measured base-line let him view the tree, keeping one tube parallel with his base line. This will necessitate his adjusting the other tube to a certain angle with regard to the other one. He must register these easily done by a piece of string fastened midway between the ends of each tube; then turning his face landwards, let him describe a precisely similar triangle, which will be pretty nearly an equilateral one-if the process be accurately gone through, it will be quite and measure the distance from its apex to base. This will give the width of the river. Or he may measure the angle in degrees, and reproduce the triangle on paper to scale, and work the problem out at home. Some years since, I interested some school-boys much by putting them up to the dodge. I hope it may be useful to "Enquirer."H. P. [4415.]-CURIOUS PROBLEM.-"Saul Rymea" asks us, in page 478, What would be the result if an irresistible force came in contact with an immovable body? In the first place, I should like to know how this gentleman proposes to define the expression, an "irresistible force;" at what point does anything obtain the property of being "irresistible ?" Secondly, What is an immovAll bodies with which we are at present acquainted are both movable and moving.-S. A. R. [4415.]-CURIOUS PROBLEM.-Very! An "irresistible" force comes into contact with an "immovable" body-well. Why, sir, it would be a case of the Kilkenny cats-only there would be no tale to tell.-H. P. able body? [4415.]-CURIOUS PROBLEM.-If, as I presume, "Saul Rymea" supposes his "immovable body" to be also "perfectly hard," the force with which the "irresist ible," by which I understand" perfectly hard" body would impinge upon it would be infinite, and therefore impossible in nature and inconceivable to the human mind; under such circumstances, therefore, his question is unanswerable. But if either of the two bodies be capable in the slightest degree of alteration of form by impact the "energy" is expended in producing such alteration.J. B. [4416.]-PHOTOGRAPHICAL.-Test your bath with litmus paper, if acid, add a few drops of ammonia until it is neutral; then test the strength and make it up to diaphragm of copper plate pierced with numerous small 50 or 60 grains per ounce. Take care that you do not holes, and the apparatus, for the sake of convenience, float the paper too long; one minute is quite long is usually arranged in two columns:-1, the analyzer enough for the present warm weather. I do not float 2, the rectifier. It is worked by steam at a pressur longer than 30 seconds in summer with the sample of of 5lb. or 61b. to the square inch and produced su paper I use. I should recommend " John" to change ordinary boiler. When the analyzer is under ful the paper, as it is a very bad sample if it discolours the pressure the wash is introduced at the top thro bath to the extent he says. "John" must also take pipe, to be afterwards referred to, and flows in an care that the paper is perfectly dry before printing it.tinuous stream through the holes in the diap By attention to the above points he ought to succeed; meeting in its passage with the steam, which gra strength of bath, description of toning bath, &c. Regard- the spirit which it contains. The steam, carryi if not write again and give particulars of make of paper, raises it to the boiling point and causes it to pat ing brown negatives he must give more particulars it the impure spirit, is next conveyed by messed before I can recommend a cure, but I fancy he has been close pipe to the bottom of the rectifier. This is traversed by another pipe whose convolutions an messing his bath until it is useless.-OPERATOR. [4416.]-PHOTOGRAPHICAL.-"John" may find ad- ranged horizontally throughout its entire lengha vantage in adding a little, or perhaps a good deal of end being connected with the wash reservoir and the fresh silver to his solution; 60 grains to the ounce of other with the top of the analyzer. The wash, is the water is the thing, and with this strength three minutes first instance, runs through this pipe to the s will sensitize the paper. Also make a new toning bath and, being cold, causes the watery particles de as follows:-2 grains bicarbonate of soda (common bread mixed steam and spirit to condense upon the oral soda), 2 grains gold, 8oz. water. This will give a good the pipe, whilst the vapour, richer in alcohol, ha and rapid tone. When the exciting bath becomes brown, one compartiment to the other, gradually pa the remedy is kaolin. Blend a very small quantity, just the water until it reaches the "spirit plate what will muddy the bath, and filter. The quantity of collected, and contains about 95 per albumenized paper has a good deal to do with brown alcohol.-A REVENUE OFFICER. baths. Try some other house for paper. Are you buying cheap chemicals or dealing in a second-rate house? Don't do either.-PADDY. [4418.]-SILVER COIN.-In answer to "A Young Beginner," I beg to inform him that his coin is a Roman denarius of the family of Antonia. It is one of a series struck by Mark Antony in honour of his legions. They bear: Obverse, a galley and rowers. ANT. AVG. III. VIR. R. P. C. (for Antonius Augur Triumvir Rei Publicae Constituendae; Antony Augur Triumvir, for the reestablishing of the Republic). Reverse, three military standards, the centre one surmounted by the Roman eagle. LEG. (for Legio, Legion), and the number. The first legion has LEG. PRI. (very rare); the 2nd, LEG. II.; the 3rd, III.; the 4th, IIII. or IV.; the 5th. V.; the 6th, VI.; the 7th, VII.; the 8th, VIII.; the 9th, VIIII. or IX.; the 10th, X.; the 11th, XI.; the 12th, LEG. XII., or LEG. XII. ANTIQVAE; the 13th, XIII.; the 14th XIIII., or XIV; the 15th, XV.; the 16th, XVI.; the 17th, LEG. XVII. or LEG. XVII. CLASSICAE; the 18th, XVIII. or XIIX. or LEG. XVIII. LIBVCAE; the 19th, XVIIII. or X(X.; the 20th, XX.; the 21st, XXI.; the 22nd, XXII.; the 23rd, FIG.I XXIII.; the 24th, XXIV.; the 25th, XXV.; and the last, the 26th, XXVI. One has CHORTIVM PRAETORIARVM, and another has CHORTIS SPECVLATORVM. Legions II. to XXIII., are common, and worth 2s. or 3s. each. -HENRY W. HENFREY, M. N. S., &c., &c. "" also answers this. [4423.]-PHOTOGRAPHY.-" John" and "J. B." both complain of bad tone to their photos. J. B." should not try to get his tones too black, or they become cold with my formula, which they will find in some of the and raw. I like a nice purple tint and always get it back numbers of the ENGLISH MECHANIC, and to which I dare say many of our readers can testify. The reasons may not be enough silver in the paper, or gold in the of the brown, leathery appearance may be many. There toning bath, or too much sodium, or a badly salted paper, or under-exposed priut. Old nitrate of silver baths are better than new if treated as follows:-Pour the bath permanganate of potash in 1oz. of water, and pour in (a into a large-mouthed bottle, then take about 1gr. of pure drop at a time) every three or four minutes. The reason for not pouring it all in at once is, because then it would turn nearly all the silver in your bath into permanganate of silver. Now shake this well and let settle. When you see the bath has a slight pinkish tone you may be sure that all organic matter is expelled the bath; place it in strong sunlight for about a week or in diffused light for a fortnight. There will be a precipitate; decant or filter (always keeping the bottle steady). This done, add fresh bath to make up for loss, at the rate of 60grs. per ounce for positive, and 50grs. per ounce for negative. Now test your bath for sensitiveness; if not sufficiently sensitive add more silver, always weighing. In fact, weigh everything. "John " need not be at all surprised at the bath discolouring after a dozen sheets, when I tell him that the same thing has occurred to me after two sheets. All that has to be done is to filter the bath through kaolin and add silver to make up for loss. What does "John" want with black negatives? Nothing can be finer than a good brown negative, always providing, of course, the shadows are clear. And now let me once in back numbers, and success to them and all other more advise them to look at my descriptions of formula fellow-workers in the "black art." If they have not enough, let them "ask for more," like Oliver Twist.Mus. [4424] COFFEY'S APPARATUS FOR DISTILLATION.-This apparatus differs in construction from all ordinary forms of still, for by its use a pure marketable spirit can be produced from the fermented wash by one distillation. It consists of a number of rectangular frames of wood about a foot each in depth, and of an area proportionate to the quantity of wash to be distilled in a given time. These are superimposel horizontally upon each other, each being furnished with a [4427.)-CASE HARDENING.—If “W. H2*£ zake his cylinder red hot and then plunge it a pers with powdered prussiate of potash, he winkiel enough to resist filing.-SEMPER PARATUS [4427.)-CASE HARDENING.-I do not in! mo case harden with prussiate of potash, in p your work would scale in the fire. But it mad smooth afterwards, and what will a little s then? If it is of iron a little hardening woal bat perhaps, but it should be of steel, and cast as shear. I once made one of the latter, and will another. If of cast steel, as it should be, and wel ta, it need not be hardened at all. It is not like a m that is everlasting by running with heavy pressin E it. It never does more with any stress on it except t drilling, and very little then, and at all other ans held fast by its set-screw. I would rather fit th double-bearing mandrels than one hardened back ceme cylinder.-J. K. P. trical perspective with a circle on each fa the lines then, ON√M N2 + M 02 = J2 and, A N = √A M2 + M N2 = √3′′ angle N A M and, therefore, A A M N is similar to AO AN, and the = angle ON A. Now to find the s portions of the projected circles. As every circle be supposed surrounded by a square, the side of squ obviously equals the diameter of the circle, or JF O B, or, that is to say, J F is the measured diameter of the circle to be projected. Measure off A P = JF, 62 draw PR perpendicular, then G K = PR and SL A R, and this holds good for any sized circle, as the are all exactly in the same proportion. Of course isometrical drawing comes out larger than a perspecti one, as the vanishing lines are not foreshortened, he exhibited of their full length, and the amount of this √3 1.782 No2 1-225, or 221 per cent. larger 1-414 lineal dimension. I do not give the proof of the last two sentences, as any one may easily make it out for himsel with a slight knowledge of geometry and of the princi ples of projection.-J. K. P. crease is = [4433.]-MARKING COTTON CLOTH.-If "B. D. F." will get some ordinary, but clean, gas tar, and put it into an iron pan, and slowly drive off by heat the gas re maining, he may then apply it to marking goods of any sort by a stamp or otherwise, and it will resist a attempts at discharge by acid or alkali, but it will not show white. (This is used by all bleachers and dyers in Lancashire.)-WAHSROF. [4434.]-TAPS AND DIES.-TO W. REED.-A lefthanded male screw may be made from a right-handed tap, with a specially made screw-stock or equivalent contrivance in which the blank to be screwed is steadied on one side by a blank die, and has the teeth of a righthanded tap forced against it on the other. It is not worth doing, as it cannot be done well, and there are other and cheaper ways of getting a screw made if it requires doing decently. Workmen are, or used to be, supposed clever, if they knew this trick. I accidentally struck a triple thread with ordinary dies a short time since, but then I was using them only for the purpose of |