Distance apart of cylinders trans versely from centre to centre Length of connecting rods between 3 11 Heating Surface. Tubes Firebox .. 670 sq. ft. 60 22 730 The valve gear is of the "stationary "link type, and the motion is communicated to the valve spindles through rocking shafts, as shown. The arrangement of steam and exhaust pipes will be readily understood by an inspection of the engravings without special explanation. The connection between the two boges is effected in the plan adopted by Mr. Fairlie for all his later engines, the two bogie pins being connected by a pair of side or carrier frames. In dealing with such a narrow gauge as 1ft. 11 in., Mr. Fairlie had many difficulties to overcome; but he has shown by the performance of the "Little Wonder," that his system of double engine is eminently fitted for use on narrow gauge lines, and there can be little doubt that as such lines are more extensively constructed, the employment of the Fairlie system will increase also. ADMIRER. MACHINE FOR CUTTING IRREGULAR SIR. I send illustration, with description, of machine for cutting irregular forms, which has recently been patented through the Scientific American Patent Agency Office, New York. The main features of the device are, the attachments for holding, adjusting, and feeding the pillars, balusters, &c., to be cut into irregular forms or plane sides, on a table past a rotary cutter. The invention may be said to consist of a bed, with centres, for holding the blank; one of the centres being adjustable longitud pally, and furnished with a dividing plate for adjusting the blank to the cutter, and a pattern for governing through the table of the machine. A guide plate, I, or pattern adjustably attached to the bed A, serves to direct the cutting. The operator takes hold of the baluster at B, with his right hand, and with his left hand on a hand rail J, pushes the machine from him, and at the same time against the mandrel; the machine is then pulled or drawn back, and lifting the spring Catch G with the left hand, and turning the baluster with the right, one space, another side is presented to the cutting tool, thereby dressing the sides all alike, and making a thousand pieces exactly similar. After the required number have been shaped the straight bits are removed and properly shaped ones take their place, and the guide pattern is changed for one corresponding to the desired ornamental design. When this is effected, one man can do the work of twenty men, and with greater neatness and accuracy than can possibly be done by hand. At the same time the hands of the operator are perfectly safe from injury: For dressing stuff like the piece K. with squares at both ends, the centre pin, seeu at the end of the piece, is inserted in the hole through the centering head B. This machine is capable of dressing not only balusters and chair, table, desk, and counter legs, but can be used to dress hay-rake and grain-drill spokes; and stuff that has to be thrown away when finished by hand on account of knots and curls (the handsomest when finished), is dressed almost as readily as straight grained wood. J. H. T. GLASS BURNING. SIR,-I beg to return my sincere thanks to Mr. Jos. Leicester, for the trouble he has taken to answer my Query on "Glass Burning." The form of oven or kiln is quite correct; the iron slabs or trays that slide in the kiln are first covered with sifted whiting, and then smoothed off with what is called a sand plane, and then the pieces of glass are laid flat on the whiting; the process of burning can be watched by a square hole in front of the kiln, which can be closed at pleasure. I have seen pieces of glass 2in. or 3in. long and in. wide, with the flux painted on, and laid on one of the slabs, and called tests; they are taken out, tried, and by them may be known when the glass is sufficiently burnt. The letter to the Editor, in answer to me, describes the silver melted in a crucible, and antimony as a flux, but did not say whether they are to be melted together or in what proportions; if the writer would kindly say something upon the subject through the medium of the MECHANIC, it will greatly oblige me, and perhaps many others. GUSTAVA KNOX. DARK LINES IN THE SPECTRUM. SIR. In reply to your observations on my letter, p. 183, I beg to observe I did not state my inability to give any evidence at all to Mr. Proctor, as that would not be true, but the spectroscopic evidence required from me in the letter on p. 130. I have, however, no objection to give reasons for considering the dark lines in the solar spectrum entirely atmospheric. When Bunsen and Kirchhoff arrived at the conclusion that the dark lines were of solar origin, they considered the sun an incandescent body surrounded by a luminous atmosphere; but later researches represent it as a non-luminous globe, surrounded by matter in a state of inten-e chemical action. If this is correct, the only foundation for the supposition of the dark lines being solar is the great depth of the photosphere and the outer and less luminous envelope absorbing certain of the rays emitted by the inner and brighter portion. Before adopting this hypothesis, would it not be well to ascertain whether the earth is not also enveloped by matter capable also of a similar, though less intense, chemical action? I apprehend there is sufficient proof that such is the fact; and if so, the origin of dark lines in the spectrum of any luminous body outside the earth's atmosphere is unmistakeable. READINGS FROM THE GLOBES. T. A. SIR,-It may not be out of place at the present tim when some of your subscribers are inquiring abou t globes and longitude, to offer a few remarks (addressed chiefly to juniors), on the uses of those instructive instruments. The proofs of the roundity and motions of the earth which have been lately given in these columns by Mr. Proctor, have shown that the earth is of a globular form, and the phenomena which the globes illustrate, rest upon this supposition, and can be accounted for easily on this principle, for if the earth were not round, the time would of course be the same in all parts of the world at the same time, and we should have no difference in longitude. Different countries take different meridians, as the line from which to reckon longitude; generally speaking, the capitals of their own country, whilst England reckons her longitude from Greenwich Observatory; hence, if we wish to know the difference of time or longitude between two places, we have only to ascertain the longitude of each, which, supposing the globes are accurate, is a very simple process, and then subtract them, if they are of the same name, but add them if one is east longitude and the other west longitude. As the globe turns on its axis from west to east, those who live in west longitude must have their time earlier than those living in east longitude, because they will not come into the enlightened hemisphere so soon. Having, then, ascertained the difference of longitude by bringing each place to the brazen meridian, and then noticing the figures on the equator, we can obtain the difference of time, and vice versa. Longitude may be converted into time by dividing by 15, and reckoning each degree over as four minutes; and time may be converted into longitude, as every sailor knows, and hence vessels take out chronometers with them for this purpose. To convert time into longitude we must multiply each hour by 15, and reckon every four minutes over as one degree. The difference in longitude gives rise to other differences, as periæci, antæci, and antipodes. The periæci, for instance, are those who live in opposite longitudes, but in the same latitude. By noticing the etymology of the word Ept around, and oukew to dwell, we shall the better comprehend its meaning; thus in the figure, suppose we lived at B on the globe, our periæci would live at A, just 180° away from us, and nothing can show more clearly than this, that the earth is round, and turns on its axis, for in consequence of doing so, when it is 12 o'clock at noon at B, it is 12 o'clock at night at A. and vice versa, but since all in the same latitude must have an equal share of the sun's rays during the day, to the other, and of course the seasons to each of these the length of the day to the one is the length of night must be the same, for all those in the same latitude have winter at the same time, as well as the other seasons. The antæci, however, derived from avr, opposite to, and otKew to dwell, are those who live in the same longitude but in opposite latitudes: that is, the antæei to N are those, supposing there are any, the people who live at E. have their antæei at F, and who live at S., and the antæci to 23 N. latitude, are those living at 259 S. latitude, and the consequence is, that their time is exactly the same, but the length of the day to the one, forms the length of the night to the other; that is, if E has two months' day, F has two months' night at the same time, but their seasons are opposite, because they live in opposite hemispheres, and when Boreas, bringing snows, reigns in one, the mild breezes of summer blow in the other. But again, if people live in opposite latitudes and longitudes, they are called antipodes, from avri opposite to, and TоUÇ, the foot, because their feet are opposite to ours, and as the sun, owing to the rotundity of the earth, can only shine over half the globe at once, it is night with our antipodes when it is day with us; and if their manners and customs are the same, when they are enjoying "Tired nature's sweet restorer, balmy sleep," we are busy at our several duties, either in work, busithe seasons are also different. This interesting subject ness, the counting-house, or the Stock Exchange; and might be carried farther, and although elementary truths, familiar to the astronomer and geographer, they might still prove of service to some whose pur. suits prevent them from consulting and studying larger treatises. Should you deem these few remarks worthy of a place in your periodical, I will follow them up with more observations upon the same subject. T. S. H. THE SALTAIRE LATHE. SIR,-I received your last monthly number only a few days ago, and to my great surprise saw on page 52, an illustration of Titus Salt, Esq.'s, lathe, as it was published without my knowledge or consent. In November last Mr. Northcote wrote to me requesting the loan of the drawings of Mr. Salt's lathe, for the purpose of publishing them, together with a description of the working of the lathe, &c. Mr. Northcote being a perfect stranger to me, I answered that I had a decided objection to do so, unless it was done efficiently, with details, and a full description, accompanied with specimens of work produced by means of the different parts of the lathe and apparatus, and I added that I thought it could only be done in a separate publication, and that I should require some time to put it together, so as to render it intelligible and useful to amateurs and others; these conditions did not meet Mr. N.'s views, and there ended the matter. I afterwards read a letter from Mr. Evaus to the MECHANIC, in which be says that the lathe belonging to Mr. Salt was almost exclusively made at his factory, the outlines of the designs having been prepared by Mr. Smith, of Jersey. Now, I beg to state, the most part of the lathe was made at Saltaire. Mr. Salt, having decided to have the lathe finished in London, went to Mr. Evans, and referred him to me. I give you a copy of Mr. Evans' letter to me : "London, Feb. 24, 1866. "104, Wardour-street, Soho. "Sir,-Some days ago I had the honour of a visit to Saltaire, to consult with Titus Salt, Jun., Esq., respecting the making and completing his lathe, which he had begun under your directions; we inspected all the drawings you had sent him, and I was put in possession of your ideas upon the several motions and appliestions to be attached thereto, and he has forwarded the lathe to town; he has suggested also that it would be advisable for me to pay you a visit to consult with you, which I purpose doing with your kind permis sion. Since the receipt of the lathe I have received a letter from Mr. Salt, wherein he mentions that without an understanding with me that your ideas should be kept private you are not disposed to give the benefit of your experience. Now, Sir, I trust I shall be able to entirely remove any scruple you may have in the matter. I have been engaged for many years in the making of models and machinery, and carrying out the ideas of inventors and gentlemen amateurs; and I will undertake that mo original idea of yours shall be made public or manufactured without your permission first had and obtained. I hope and trust you will not have any doubt on the subject, but permit me the honour of waiting benefit of a personal interview. From your drawings upon you at your residence, so that I may have the be mature, and of great value. I hope to have the and particulars given in detail, your experience must honour of a reply, stating when it will suit your convenience to receive me.-I have the honour to be. Sir, W. J. EVANS. your most obedient servant, "To John Smith, Esq., Jersey." Now, in presence of such assurances, I wrote to say I was ready to receive him. He came over to Jersey; I showed him my own lathe, and all the apparatus (my own work, and the result of many years' experieace); he had all the information that was necessary: he noted all the details, and made many sketches and memoranda; I afterwards sent him many drawings of details, and the whole of the work was carried out under my supervision; I visited London many times for that purpose, and it was with great difficulty I got the lathe as complete as it is now, having been obfiged to order many parts to be cast aside and replaced by others, according to my original design. I also took Mr. E. to see a lathe that I had made for a friend of mine in Jersey, the same in nearly every point as Mr. Salt's. Now, Sir, I think this is rather more than mere outlines. On page 88, your correspondent J. K. P.," says :"I happen to know that a great part of the lathe which was made at Saltaire, and which came to Mr. Evans', 102. Wardour-street, to be finished, was put on one side, and entirely remade"; this statement is not true. I am not aware that the slide rest has any steel wheels: the saddle has. "J. K. P." hopes that his (Mr. E.'s) mind is not oppressed with the recollection of having made for such a lathe such a chuck as the face plate with four dogs sticking out of it, which is shown on the floor in the picture. Allow me, Sir, to tell J. K. P." that the shuck was not mine, nor made with my consent or knowledge. On page 114, "J. K. P." again states that there are several small wheels in the slide rest. I am not aware that there are either wheels or rack. The saddle was from my design; the slide rest was not what I wished to have made, but very different, and on Mr. Evans' plan. Now, Sir, I will put a question to "J. K. P." How came he to know all this in presence of Mr. E.'s engagement not to show the lathe, or make it public? Either Mr. E. must have forgotten his promise, or " J. K. P.'s" letters are manufactured at 134, Wardourstreet. JOHN SMITH, St. Heliers, Jersey. [Most assuredly our readers have heard enough about the designer and inventor of this lathe.] COMMERCE AND TRADE. SIR,-Questions ia political economy are, I fear, hardly suited to your columns. To admit the discussion of them would be like the "letting in of water. The deduction I should draw-briefly stated-from" S. Rymea's" statistics of the trade of the United Kingdom for the year 1868, is, that for £179'000,000 of exports, we managed to purchase £294,000,000 of imports; a profitable year's business, surely. I have no doubt, however, that there was a considerable export of gold, of which no mention is made in the statistics given, and without which no conclusion can be arrived at as to the net results of the commercial transactions of that EXCHANGE. year. TOOL HOLDER. SIR-The enclosed rude pencil-sketch represents a tool-holder or simple slide-rest which I have constructed. It will be found useful to amateurs in the absence of a regular one. I think the following description will explain it :-A lathe shears; B socket or holder, which can be adjusted to the shears in any position by the nut C; D frame of slide-rest, forged out of malleable iron, gin. by lin.; E slider made of iron tubing, with a square flange soldered to the under side, which slides in grooves or key-seats in the eyes FF; G the screw upon which the slider travels, and which can be brought to bear upon the work with the requisite pressure by turning the handle H.; II two pinching screws, which can be pressed gently against the upper surface of the slider, so as to prevent vibration while at work; K the cutter, which is held in position by the screw L. I have several cutters, all of which are chamfered differently at both enda, so that either end may be used, according to the work required. It will also be seen that the cutter may be placed at right angles to the slide by putting it through the hole M. It will then cut parallel, by tightening up the screw P, and turning the handle. This little slide-rest is particularly adapted to work to be turned on the face-plate, such as small cylinder covers, &c., where ornamentation by beading or grooving is required. As a kind of circular motion may be given by turning the slide-rest on its shank N, all kinds of OG patterns similar to the handle the holder must be bored out true, and the shank may be turned by feeding with screw G. Of course and freedom from vibration; and when required to be turned down to a good fit, in order to ensure stability rigid, it can be held quite tight by the screw P. I have done several jobs with it, and I find it a great improvement on the hand-tool system, as it permits the operator to turn the lathe for himself. I don't know whether this idea is original or not, but I assure you it is quite new to me. CHRISTOPHER FALLON, Barthgate-by-Edinburgh. THE REPUTED FIGURE AND MOTIONS OF THE EARTH.-THE EARTH'S ROTATION. (Third and concluding Letter.) SIR,-I shall have occasion again to revert to the optical deception I noticed in my last, when I come to consider the question of "Parallax," and will not now say anything further on the measure of a degree; except just to notice that if we take anything short of the true diameter of the circle as the base, the division of less than one-half of that circle into 180 parts is an error, and that the arguments adduced by Mr. Proctor in his fourth chapter on the "Determining the Shape of the Earth," are consequently equally erroneous. I have noticed Mr. Proctor's arguments on the "Diurnal Motion of the Sun and Stars," and also his admission with reference to the system advocated by Tycho Brahe, which, to a great extent, renders further reply on my part superfluous, I shall therefore at once examine his arguments on the gyroscope and pendulum experiments, in proof of the earth's rotation. Suppose we set a pendulum swinging due north and south in a carriage running due south, and suppose the horses' heads are all at once turned to the west, is there anything wonderful in the pendulum (freely suspended) still continuing to oscillate due north and south? Would not the force caused by the falling weight be still in the same direction, although the direction of the course pursued by the carriage be changed 50 times? Such direction of such force would be the same, and the greater wonder would be if it were not 80. But how does this argument fit when examined fairly? If we are really passing from west to east at the rate of nearly 1500 feet in a second of time, how comes a pendulum, set swinging due east and west to continue to do so? Would not such a speed cause a greater impulse to be imparted to it one way than the other? As we must bear in mind that the point of suspension is attached to the supposed rotating body, and also with a string from a suspension of 17ft. 9in., as in the experiment noted. When the pendulum was at the limit of its swing to the east, the support will have passed nearly 1500ft. in far less time than the pendulum swing will complete the proper arc of a circle B C (Fig. 1). For instance, let WE be the direction of the earth's rotation, as shown by the arrow, then supposing the penduJum bob is at B, the support will have passed nearly 1500ft. towards E in far less time than it will take the said bob to reach C. We will suppose, for the sake of easy illustration, that the pendulum makes one swing from B to C in a second of time, how is it possible for it ever to reach D, to say nothing of its reaching C, when we find that the support itself has travelled more than 80 times as far as the length of the pendulum during the time taken by one motion of he same? But we will further suppose the pendulum to be set swinging due north and south, and the earth rotates from west to east, how are we to account for this great speed not interfering with the oscillations of the same? us the current of motion will act directly across the plaue of its oscillation, and, as a matter of course, would materially interfere with its so-called gravity, and alter its course to the west and not to the east, out of all proportion to anything noted in the experiments adduced by Mr. Proctor. I am aware that it is said that the pendulum experiments prove that the alteration in the plane of oscillation, proves that the earth rotates about an axis, causing our day and night; that if a pendulum could be adjusted at one of the poles, or at the equator, the oscillation would continue true, and that because we earth's surface, this alteration in the plane of oscilla are situated midway between these two points of the east; but, as I have before shown, it is impossible tion is attributed to the earth's moving from west to between our position and the equator. I now ask, would it not be strange (putting aside the question of rotation altogether) if a pendulum, such as Mr. Worms made use of, did not vary in its oscillations place it where he will, with a ball of brass 40lb., and a steel wire 17ft. 9in. long, both liable to magnetic influence. The greatest wonder is that we find men so wedded to theory as to apparently overlook perhaps the most important and least understood principle in nature, and by silence disclaim, as it were, the existence of such a force and principle as terrestrial magnetisin-a force continually changing both in direction and power-a principle whose source and mode of action our best philosophers cannot explain. The gyroscope is but another repetition of that force and direction of motion we have seen depicted by the pendulum experiment. Who ever imagined that if any disc or wheel, for instance, was firmly fixed to an axis, and free to rotate upon it, that it would not do so, if sufficient force were given to it? And we know well where force is applied to weight, and this moves in a given direction, force must be applied to alter that direction, or it would continue to move in the same course until such force is spent. It is when a combination of forces and motions are called forth, which renders the matter somewhat perplexing, as the gyroscope, for instance. But to treat of this principle fully would occupy a volume itself, and cannot, therefore, be satisfactorily treated here, but I may just say. when the action of the gyroscope comes to be fully understood, and worked out in detail, our present dynamical theories will not only be found wofully incomplete, but erroneous also. If this experimental gyroscope had been placed on a rapidly rotating sphere, which is the only way in which the experiment can be fairly tried, would it "travel against " the sphere in rapid rotation? I maintain that it will not. Suppose the direction of the earth's rotation is from west to east, and that the speed is after the rate of 17 miles per minute, and let the line of motion be perfectly straight, for the sake of simplicity, what instrument, supported on a "pointed pivot," could remain true for an instant, or withstand the directive force of such a motion? But how is it that this instrument gives the same result relatively, no matter in what direction it is put into action, if its motion is "against the direction of the earth's rotation?" How is it that it can travel at all in other positions with such an enormous speed to overcome, especially when we consider the great nicety, and such slender connection through its supports that it has with the earth? Again, there must be continual application of power if the motion of a gyroscope is to be of long duration, otherwise the disc will cease to act. Here, then, two questions present themselves:. 1st, Does the continued application of power tend to alter the direction of the axis of the disc; and 2nd, Does not the influence of motion by a species of centripetal force give the results as seen? It is plain it is more owing to the unexplained laws of motion than to the earth s rotation. I come now to consider the other reasons given by Mr. Proctor in support of the assumption that the earth is globular, aud, therefore, that it rotates about its axis. He remarks that the "sailor voyaging in the southern seas, estimates his progress strictly according to those results which follow from the globe figure of the earth," when the sky is clouded. I may ask, Is there anything remarkable in his being able to accomplish this, with proper means and appliances at his disposal? He knows by the chart the relative position of one country or island to another, and whether he goes in a straight line, or straight round, it really matters not, so that his position is clearly known and the relative distances correctly recorded. The greater wonder would be if he could not do so. The fact that the "upper masts of a vessel " outward bound "may be out of focus when the sea horizon is brought into focus" is fully explained in my remarks on Fig. 3, iu my last letter (ENGLISH MECHANic, page 135), and has simply reference to the limit of vision as the observer's horizon. But in order to show clearly that the lines of vision generally appear curved, we must examine their bearing in reference to I say "generally," because there is on distance. record extraordinary peculiarities in some people's power of vision (see Dr. Ussher's papers on "The Eye, The man in the Mauritius who "was and Something About It," ENGLISH MECHANIC, Vol. X., page 295). able to announce the approach of vessels days before they arrived" had a peculiar power of vision, which, so far from being general, is entirely exceptional, and the fact of our gifted author recording this, in keeping with his extensive knowledge of the organs of vision, point clearly to the cause proceeding from the peculiar formation of the human eye. I am afraid I may have done wrong in alluding to Dr. Ussher's admirable paper in support of my position, but I, at the same time, hope Mr. Proctor will not sharpen his ironical sword for use upon him. I cannot resist a smile when I ask Mr. Proctor if the man, when he announced the approach of these vessels (when no other eye could see them), saw through the ocean, which he must do if the surface is really convex. It is not necessary that I should enter at length into "the shape of the earth's shadow as seen during a lunar eclipse." Enough has been acknowledged by Mr. Proctor on page 242, Vol. X., of the ENGLISH MECHANIC to cast a doubt on the minds of most men as to the correctness of the present theories, especially when we find it acknowledged by our author that" nothing but the complete survey" (described in Chapter IV. of his papers)" can be held to be a satisfactory proof." When that shall be shown to fail, what is to become of our boasted system of modern astronomy? The "peculiarity noticed by balloonists" is accounted for by natural laws. When he ascends from the ground the earth gradually assumes more of a concave shape, until it has the appearance of a huge basin. If he looks down upon the earth below him, the rays of vision pass perpendicularly through the atmosphere; but if he casts a look at the distant horizon, at C or D, the rays of vision are bent towards the perpendicular; while if he looks upwards into a rarer atmosphere, the sky assumes a convex appearance, as the rays are bent (looking towards C or D) from the perpendicular, A B. In short, many of our theories are based upon wrong conclusions, which the plainest principles of vision will illustrate and explain. I have now brought my remarks on the Earth's Rotation to a close. I might have adduced other arguments in favour of my position, but I think I have produced sufficient to induce serious thought on a matter too much confined within the sphere of dogmatic teaching. JOHN BEARDSLEY. [At the foot of Mr. Beardsley's last letter we offered an apology for inserting it; now we must say a word or two in explanation. Almost immediately after the appearance of Mr. Proctor's admirable series of articles on the Earth, we received a letter from Mr. Beardsley, saying that he was preparing, in a series of letters, an answer to Mr. Proctor, and asking us whether we would insert it. Believing in free discussion, and believing also, from the tone of Mr. Beardsley's letter, that he had something worth saying, we said "Yes." Having given a promise, we felt bound to redeem it; but we must say that had we any notion at the time of the probable character and quality of Mr. Beardsley's reply, we should not have consented to allow him space. Possibly, however, the insertion of the letters will do good, as they show on what a narrow and shaky basis the theory of the earth being a plane rests upon.-ED. E.M.] THE MOTIONS OF THE MOON AND EARTH. SIR,-Will you allow me a small space to give my views respecting the motions of the earth and moon, as they differ in one or two particulars from the generally-received system of astronomy? About the year 1854 I felt a wish to construct a machine which should truthfully represent the motions of the earth, more particularly with reference to the changes of the sea sons. duced. Another most interesting fact in connection tion. ON VELOCIPEDE CONSTRUCTION. is a moderately good travelling machine on the fevel CHOOSING ONE'S BELIEF. SIR,-In the current number of our journal is a letter from "Saul Rymea "on the rotation of the earth &c., which, though an admirable letterin most respects, contains one statement which is decidedly wroug; he talks about people choosing their belief, now it is possible for any man to choose his belief; for instance, just let "Saul Rymen" try to believe, say for half-an-hour, in the theories of Parallax," John Hampden, or any of that fraternity, and he will see the impossibility of any one choosing his belief. but I cannot do so, the evidence is too strong the other There are many things which I should like to believe, way. I do not believe the earth to be flat like a pancake, but it is not from a wish to believe it globular, or rather spheroidal. I can no more doubt the form of the earth than I can doubt that the sun will rise to-morrow morning, and this is the case with everything else, from the greatest to the smallest. We must believe according to the evidence presented to our senses, and not according to our own wishes or choice. T. COOKE. ASTRONOMICAL. SIR,-I thank "Omicron " for the explanation given as to the formula respecting the brilliancy of Venus. If he had time I could wish him to insert anew the formula given at page 614, Vol. X. for finding the longitude and latitude of a heavenly body from its right ascension and declination, it being impossible for young astronomers to make anything of it as there printed. Of course I am a little versed in these things or I should have been puzzled with it too. G. FIRTI. QUADRATICS REDUCIBLE TO QUADRATICS (Continued from page 131.) SIR," Bernardin" is correct in his supposition, but I intend simply going the shortest way to work in order to get the answers given by Mr. Todhunter. I think without egotism that I may say the solution given by me is similar to that which would be given by Mr. Todhunter himself, or I greatly mistake his letterpress upon the subject. But (7.) x + 2 (a x) + c = 0 x + 2 √ α √ x + {√ ap2 = a - c (8.) 3 24 (9.) 8 x 3 xn + 2 xn = 16. 3 xn HYGIENE OF VENTILATION. SIR,-Many plans for effecting this desirable object In considering the subject with this view, the have been carried out, both in public as well as in conviction forced itself upon me that the earth has a private buildings, and many more proposed, but all I should be glad if "Bernardin "would explain why third motion not taken into account by astronomers- have, more or less, met with objections on various such examples as the above are inserted. Like namely, an annual rotatory motion on an axis perpen-accounts, with the sole exception, I believe, of the "Gimel," I do not for the life of me see their utility. dicular to the plane of its orbit, and on the same prin- Silvester system, adopted in the infirmary at Derby. As a tutor I know pupils hate and detest the sight of ciple that the moon has no axial motion. I am aware The method proposed and published by me some the public papers some short time after I first pro- manufactories, is simple in its character, and if pro- the use, therefore, of giving solutions to such questions, that a controversy on this question was carried on in years since, for the ventilation of phosphorus match abstract questions containing the nth or any powers not expressed by arithmetical numbers. I scarcely see pounded my theory, but I never got a sight of any of perly carried out, would scarcely meet with objectors, but to such as wish it the above may be solved by the correspondence; therefore, I am entirely ignorant and is quite independent of doors and windows. The multiplying by 3 xn, then dividing by 3 and workof the nature of the arguments employed either pro or principle is to cause the vitiated air to pass out through the floor, and the fresh to enter through as extremely useful, as, iu some future numbers, i will ing as a quadratic. Unlike con.; so that my ideas are entirely original, so far as Gimel," I believe algebra I am aware. The new theory, as discussed at that fiue pierced ceiling in the following manner, namely: endeavour to show. time, I believe, had reference only to the case of the From the space between the floor and the ceiling moon. The principle of my theory involves some below, lead off a tube or trunk into a chimney or air very interesting and important results as regards the shaft, rising above the roof, capped with a directearth, and which are well worthy a thorough investi- acting cowl, that is to say, mouth from the wind. gation. But to the point. Astronomers tell us that In a similar manner lead off a flue from the space the fact of the moon always presenting the same face between the ceiling and the floor above, into another to the earth proves that she turns on her axis in the chimney or air shaft, capped with a reverse acting same period of time that she performs her revolution cowl, mouth to the wind. round the earth. I maintain that this fact proves the contrary; for if the moon turned on its axis as described, each hemisphere would be successively presented to the earth. The phenomena presented by the moon are entirely the results of its orbital motion in conjunction with its annual journey round the sun. I will give one illustration of my view. Suppose a ball fixed to one extremity of a rod, the other being held in a person's hand, the arm and rod being maintained in a horizontal direction, the person turns round, carrying the rod and ball with him. The ball makes a revolution round the person, and while the same hemisphere is constantly turned towards the person, it is successively presented to each point of the compass. The ball has a motion about a centre; but where is that centre? Not within itself; it cannot turn about its own axis in the way supposed without being detached from the rod. The centre of motion is the person holding the rod, about which the rod and ball turn as a common centre, and producing precisely similar results to those produced by the moon's revolution round the earth. 5 (10.) x + = 3 (multiplying by 2 x1) 13 2 x1 + 5 = (dividing by 2 and taking 4 across). In order to obtain a fine pierced ceiling, all we have to do is to leave out all the plastering on the laths, which in this case should be sawn, not split, and set close. Sawn laths would present an even surface for colouring in distemper, or other ornamentation. The pierced floor is produced by laying down a border of fine pierced thin metal, of sufficient breadth for the size of the room. If the automatic action of the atmosphere should be deemed inadequate to perform the office of perfect ventilation, a smail stove may be placed somewhere in the upcast shaft, as is usual in our collieries. In more important cases, it may be advisable to adopt exhausting apparatus, set in motion by steam, gas, or water pressure, as in the present mode of blowing large organs; and it may be observed at the same time, that the friction of rarefied air in the exhausting process, is greatly less than that of compressed air in the blowing tubes, as proved by the fact that after a certain length, the most powerful blast will fail to put out a candle at the farther end, but by exhaustion it is immediately extinguished at the same distance. p. 167, an account of a new planisphere by a sepaI will now endeavour to state my views respecting There is an obstacle to the introduction of this mode of Greenock. I beg to say I have or the motion of the earth. In order to produce the of ventilation, that it cannot be the subject of a changes of the seasons, I maintain that it is necessary patent right, and therefore it is not very likely that it two discs, one opaque, and ts: these conclutt on the way for years, upon the der it intelligible and to suppose a third motion, such as I have described in will ever be brought to bear. The products of the which, when it is complete, connection with the annual journey of the earth round combustion of gas, or other lights, should always be number of interesting problem And here a most interesting fact presents carried off independently of ventilation by any mode altitude and azimuth of any at the lathe belog By supposing a slight discrepancy in the by the arrangement perfected by the late Professor luminary. When the British Agely made at his fa periods of the orbital and the axial motion that I Faraday. Contend for, the precession of the equinoxes is pro HENRY W. REVELEY, Reading. wich, August, 1868, I applied ving been prepar SILVERING GLASS SPECULA. SIR,-In reply to letter by Mr. James Gray, at p. 163, I beg to inform him that in silvering by the Rochelle salt plan, I found a marked improvement by suspending the glass in the liquor instead of covering the glass with it. I found in the latter way that a thick film formed on the upper surface of the pool of liquor, and this seemed to keep the light from the surface of the glass, and stop the action there, but when the speculum was reversed and hung as in Browning's method, the sun shone strongly through the glass; and by this means several very decent films have been obtained. With respect to his query about the size of small mirror, if the question is not undeserving of a formula, I beg to send the following: Let A the aperture of speculum f its focal length a = aperture of field lens (lowest power) me semble qu'on est force de considérer les étoiles qui of great good. It is in no fault-finding mood that I beg to draw your attention to one or two slight errors which occur in a letter, pp. 157 and 158. First, the Howe and Thomas shuttles are exactly the same in size as regards thickness. I measured a B Howe and What you say you have indicated is precisely what a No. 2 7-16 Thomas, those being the corresponding was first suggested years ago by Sir W. Herschel, and, machines. Thus, in this particular their virtues are as I said before, was actually discovered and published equal. Then, as regards the quantity of thread the in France several years ago; therefore it is not a different shuttles hold, I find Singer holds most, novelty. Thomas next, and Howe the least, the Thomas shuttle "J'ai été amené à remarquer que le groupe nom- reel being in, longer between brass ends, and also breux d'étoiles autour diy de Persée sitrouve presque larger in diameter than Howe's. I quite agree with exactement à l'intersection de la voie lactée et du all that is said respecting the Singer shuttle, or crank grand cercle qu'on peut appeler l'équateur du mouve-action, it being far from correct. At the same time, ment solaire, cest-à-dire, du grand cercle qui a pour the cams of the machines he mentions, in my opinion pôle le point vers lequel se dirige le soleil. Cette cirare far from being up to the mark. Let me begin constance pourrait faire regarder ce groupe, plus qui with the Thomas cam. This moves the shuttle to its celui des pleiades, comme le centre du système sideral, furthest extremity before the needle moves upwards; si ce système avait un centre que nous puissons shuttle carrier and shuttle, when the shuttle thread is hence the needle thread is pulled up between end of reconnoitre." Certainly the sidereal system has a centre, and not only we can, but we do know it, and at its tightest. This must injure the upper thread to we can see it with naked eyes; but it is not in the a certain extent, and forces the operator to keep a direction of of Persee, which, relatively to our sun, loose tension in shuttle. χ Again, in the Howe the upper thread is pulled from between driver and shutis almost in the same direction as the Pleiades. The tle at an angle, which also has the effect of injuring the upper thread, and causes irregularity in the stitching if the needle thread should be uneven. Now, I have a machine on Howe's principle made by Messrs. Jones and Co., in which all this is obviated. The action of the cam forces the shuttle forward directly opposite the needle, then pauses while the needle in its upward movement, disengages the upper thread from between the shuttle and carrier, then, simultaneously with the needle, draws its thread tight. This, in my opinion, is the correct theory, and practice confirms it, as I find I can do tighter and better work on a machine of this description than on any of the others. Hyades would be nearer still, as the real place is in d the distance the image is thrown out from the direction of the neck of the unicorn. the axis of telescope Then x= minor axis of small mirror TO R. A. PROCTOR, ESQ. SIR,-I am only a most unfortunate lover of science, and, as such, I most earnestly endeavour to keep myself apace with what appears in the scientific world, as much as I possibly can. Of course, I read your very able productions, both in English and French periodicals, and mainly in the ENGLISH MECHANIC. Not knowing your personal address, I venture to write to you through the medium of the latter most valuable paper, in the hope that these, my lines, will reach you. Being French, I beg you make allowance for my incorrect language. Some time since I was struck in reading in a French review a few words on your new theory of the milky way. As it was but an abstract, I could not make much of it, and could guess nothing as to the principle aud law upon which it stands; but I remained convinced that you are not acquainted with the physical law applicable to this great sidereal circle and its mode of formation, as when the law of a phenomenon is known all theories respecting it are at an end. I hope it will not be trespassing on politeness and personal respect and consideration to humbly tell you that such a law, such a mode of formation, are known, have been printed and published now for several years, and that, for me, at least, they do away with all uncertainty respecting the real nature of the galaxy, its form, composition, rules, &c., and its absolute mathematical connection with the universal sidereal system. The publication of the great work in which the details are contained was began in 1858-12 years ago-but the part of it specially relating to celestial bodies and the galaxy, appeared in 1866, under the title Physique Céleste;' it consists of about 300 pp. Svo., forming 3 volumes. When at Exeter, at the meeting of the British Association, in August last, I had the pleasure to present a copy of it to Mr. N. Lockyer. Since this I sent one to Mr. Warren-Delarue, and I should very much like to know the opinion of these savants upon works affecting so high a preten sion. I do not think it necessary to enter into any more details on the subject, and beg respectfully to refor you to the annexed vouchers. How fortunate you are in England! Whoever has a new idea or conception upon any hitherto unexplained subject is sure to find a press ready to make it public Day, to take up matters so as to set forth any parcel of truth it may contain, and discussion never fails to anyone. Not so in France, I am sorry to say. Money is the only god now worshipped. No Editor will publish anything, however valuable, unless he is largely paid for it; and even under such conditious, if the new idea is likely to disagree with M.A.'s or M. B.'s theories, as these autorités savantes ordinarily bring water to the mill, there is no hope of our obtaining anything like publicity, were it for a Newtonian discovery. No one can form an idea of the check that science receives in France from the extinguishing power of esprit de corps and journalism. If we are principal causes. I tried to contend against such a now so far behind other nations, this is one of the regrettable state of things in creating the Reforme Scientifique, of which I here send a few numbers for your inspection, but I was not sufficiently supported. ful, is that English subscribers were my best supA thing worth mentioning, and for which I am grateporters; some of them went so far as to offer me to double the price of subscription to enable me to go on, which, however, I did not do, being alone. Should you think proper to answer this letter, and have used the Thomas, the Singer, Howe (American), JUMPING FROM A TRAIN. SIR,-The view expressed by "O. W. W. G." is I had not touched on the undoubtedly the true one. way in which the backward jump should be effected; only of this I was and am certain, from experiments of my own, that by jumping energetically backwards (really backwards as regards attitude, as well as regards motion of train or carriage) an important aliquot part of the forward motion may be neutralised. to make any remarks upon its contents, I should be from experiments I made some years since from In the case of a runaway open carriage, I am certain, trucks moving at different rates, that a very sharp very glad to see it in the ENGLISH MECHANIC. spring over the back of the carriage, all the energy of the body being employed to give motion horizontally easy fall, because one can neutralise the forward from the carriage, would result in a very safe and motion almost wholly. I am sure that in some instances where I tried the experiment, the velocity of the truck must have been very nearly equal to that of a runaway carriage; but the truck had no back, so that it was easy to give an energetic spring. R. A. PROCTOR. If M. CH. RABACHE, Morchain, Somme, France. PLATINISED GAUZE BATTERY. by " Sigma," can be made with two pieces of gauze DARK LINES IN SOLAR SPECTRUM. nothing to be said by me on the point you deal with. SIR, Your comments on "T. A.'s" letter leave As regards "T. A.'s" doubts, I could have resolved them at once, had he, in his first letter, simply asked the dark lines in the solar spectrum are not due to our on what evidence physicists grounded their belief that own atmosphere. Long before Kirchhoff's great discovery (admirably MECHANIC), Brewster had noticed that certain dark described by "F.R.A.S." in the last number of the lines make their appearance when the sun is low. there are certain lines and nebulous bands (doubtless These are doubtless atmospheric. On the other hand, resolvable into lines) which are only seen, at least with ordinary spectroscopic power, when the sun is high, These are doubtless true solar lines, so faint as to be very readily obliterated. The remaining lines continue grow narrow, as "T. A." supposes they should when visible whether the sun is high or low. Nor do they the sun sinks low. It is contrary to the very essence and principles of spectroscopic science that they should grow wider as the sun sinks low. do so, or, conversely, that the atmospheric lines should, What really hap-pens is, that the latter lines grow darker, because as the sun sinks he shines through a greater and greater, depth of our atmosphere, and so the atmosphere more" completely absorbs those rays which its vapours have power to affect. Rays of greater or less refrangibility (that is, rays falling on either side of any atmospheric dark lines) our atmosphere cannot affect, let its density be increased ever so. In another number of the same French periodical I found, as translated from you, a "Mémoire préliminaire sur certains mouvements de translation des étoiles." This being more extensive, can fix one's mind upon its purport. After having read it, I feel convinced that you are yet seeking after a centre round which all the other sidereal bodies gravitate-a thing, again, that, unknown to you, no doubt, has been determined, printed, and published, long ago. In 1867 I took the liberty of sending to Mr. Glaisher, with a letter, a copy of a pamphlet entitled "Le Grand Soleil visible au centre du Système du Monde," with a celestial map representing the galaxy, with all the constellations, &c., and showing the universe in different aspects, according to physical laws. of course expected from Mr. Glaisher what I never failed to obtain from English gentlemen-that is, at least an acknowledgment of the compliment paid him in my letter, and also of the receipt of the pamphlet. I was deceived in my expectation. Mr. Glaisher remained silent-which was very easy. I send with this letter one of these pamphlets, with a rough sketch (I cannot draw) of the celestial map, for your perusal. Now will you allow me to present a few remarks "Mémoires," from which I will make some your potations in You are made to say:-"J'ai trouvé que dans published. Allow me to remind him, that at the lines do undoubtedly, pro tanto, diminish in discertaines parties du ciel, les étoiles manifestent une meeting of the Society, January 14, 1870, and pub-tinctness. tendance bien marquée à si mouvais suivant une direc-lished, Mr. Buckingham said, he had been observing tion déterminée." May I be allowed to say, that many years ago, the very celebrated W. Herschel had observed it, not as a tendency, but as a fact; and that this great man for a long time sought for a central sun, which he considered as existing, our own sun baving an orbituary motion round it? Later, Argelander made researches, but at a distance so far as 90 from its real place. He could not find it, and was then contradicted by J. Herschel, who was in the right; but as his father had attributed the movement of the bright stars to that of the sun, he dared not go text? farther. le fait que dans une grande partie du cieli adityair "On ne peut que regarder comme trés significatif mouvement commun, tel que je l'ai indiqué. I THE TELESCOPE. MR. BUCKINGHAM'S Jupiter before coming to the meeting, with the teles SEWING MACHINES. Now, it might seem that, by parity of reasoning, the solar dark lines should grow fainter as the sun sinks, but on consideration "1. A." will see that they will continue relatively as strong, whether the sun is high or low; for our atmosphere neither adds to nor subtracts from the quantity of solar vapour through which these rays have passed. The spectrum grows I cannot close this letter without gently reminding "T. A." that our physicists are too earnestly engaged in seeking after truth to overlook such very obvious considerations as are sometimes urged against their theories. Let me quote one passage, in which Kirchhoff presents a portion of his results, in order that the spirit of the true man of science may be recognised by T. A." and others : "The observed phenomenon may be explained by the supposition that the rays of light which form the solar spectrum have passed through the vapour of iron, and have thus suffered the absorption which the able cause of this coincidence, the supposition appears vapour of iron must exert. As this is the only assignto be a necessary one. These iron vapours might be contained either in the atmosphere of the sun or in that of the earth. But it is not easy to understand how our atmosphere can contain such a quantity of iron vapour as would produce the very distinct absorption lines, which we see in the solar spectrum. And this supposition is rendered still less probable by the fact that these lines do not appreciably alter when the sun approaches the horizon. It does not, on the other band, seem at all unlikely, owing to the high temperature which we must suppose the sun's atmosphere to possess, that such vapours should be present in it. Hence my observations of the solar spectrum appear to me to prove the presence of iron vapour in the solar atmosphere with as great a degree of certainty as we can attain ia any question of natural science." minder of an old discussion, as to his last remarks on which some time since I intended to have said something. He refers to a letter in Nature arguing the probability that the Moa existed during comparatively very recent periods, and was knowu to the present aboriginal races. It is, of course, impossible to come to any certainty on such a subject. and I do not pretend to any actual knowledge. The discussion, if it can be called such, arose from a joke of mine as to the cause of cannibalism being the want of animal food; "Urban" suggested that the cannibal New Zealanders had the Moa in abundance. The letter now referred to was called forth by a report of a German saran who has been exploring New Zealand, and come to the conclusion that the Moa had been This patient labourer in the field of arduous research, extinct many hundreds of years, which is my view this cautious and clear-sighted reasoner, this modest of the matter, and, further, he says that he had exaand unpretending philosopher, is one of the tricky mined the remains of ancient encampments, analaknaves," the "shifty, dodgy liars of Mr. Hampden; gous to those our savage ancestors have left in old is" one of the class of men who, next to horse-dealers caves, and found many bones of the Moa, but mostly and jockeys, bear the unenviable reputation of being of the small species, and with them those of dogs, the most tricky and unscrupulous in their assertions." gulls, and whales, but found no buman bones, indiAnd of Mr. Hampden let me say this, in passing-Icating the probability that the race which had these sources of food were not cannibals. think nothing he might write, or say, or do, could by any possibility cause scientific men even a passing annoyance; but I do hope that he will never so far try their patience as to endeavour to fix on them the stigma and deep disgrace of his approval. R. A. PROCTOR. COILS. He SIR,-Seeing D. Forbes's description of his coil (8715, p. 160), I think it a wise decision on his part to let his coil alone, for it is a very disproportionate-sized one, and I doubt if he could lengthen the spark either by winding over again, or adding more wire. The size core generally used for a coil 12in. long is about lin. diameter (8 times the size of his wire. The variety known as "soft charcoal," is the best for cores. seems to have rather a queer notion with respect to the secondary. He says" he made his coil... with a disc in the centre dividing the secondary in two, joined by a piece of copper at the bottom of the centre disc going through the disc." The usual way to divide the secondary is to wind a layer the whole length of the reel, insulate it all along with about 6 layers of tissue, then slip the disc over it and fix it there with paraffin wax, and wind away back to lin. or in. of the disc. This is rather different to joining the sec. by a "piece of copper," which, I presume, means a slip of copper. I make it a practise to seal up the edges of the tissue which are left against the sides of the ends and disc with paraffin. The spark, which might other wise travel along the tissue down to the next layer by the absence of insulation (being prevented by the thickness from going through it) would (by sealing the tissue up against the sides) be prevented from passing. I should recommend him to use a glass or vulcanite tube in. thick to enclose the core, and wind the primary directly on to it, covering the wire when wound well with insulation, and then wind the sec. on this, dispensing with lignum vitæ reels altogether. He ought to put 8lb. instead of 4lb. of sec. on a coil 12in. long, and get a 7in. spark from it. He could not use a better wire than No. 36; if he used thinner the spark would certainly be longer, but it would be thin and wiry-of no use in some experiments. I was much interested by "Urban's" last letter on the subject referring to Arabic records, but I must say that, in my present state of information as to these, I feel a strong conviction these are misunderstood. My acquaintance with Arab seamen, and especially Arab vessels, even of the present day, does not induce me to think it likely that they had explored the southern seas in the 13th century. These early Arab navigators were but wandering merchants seeking markets, or else pirates looking for goods and people to steal as they do to this day; but they were miserably equipped, provided only for short coasting trips, and without incentive to urge, or knowledge to give them courage to traverse unknown seas out of sight of land: and, further, they were unmitigated liars, as also they remain, and their tales have little more value than those of the celebrated royageur Sindbad, whose "roc," by-the-bye, was no doubt based upon some accounts of these very birds, and others of similar magnitude, natives not of New Zealand, however, but of Madagascar. At the same time it is just possible that creeping about among the eastern islands, some stragglers might have found their way through Torres Straits or round New Guinea, and then blundering on the north of Australia, been blown out to sea and struck New Zealand, The difficulty would be, in such a case (and by such means these islands were probably peopled), how they got back again, with the then existing knowledge of navigation, and unaided by the compass, unless they picked that up from some far travelling Chinese junk, as that now stagnant race of early in ventors claim to have known this instrument from very early times. However, if the Arabs spoke truly, all they prove is that the Moa existed while New Zealand was uninhabited. That by no means prevents the conclusion that they were soon killed off by the early settlers, most likely shipwrecked and starving, and that cannabalism arose after the supply was exhausted. SIGMA. tion. I was anxious to see a reply, but looked in vain, I have since tried several experiments with acids, and find the best stain to be equal parts of American potash and pearl ash-24. worth of each to about a quart of water. This will give a strong stain, it requires careful application, as the American potash is a strong solvent and will blister the hands; it softens a good paint brush once using, so I get a very common brush, and apply the staining with it. I keep it corked up in a bottle, and it is always ready for use; if it strikes too deep a colour add more water." THE HARMONIOUS BLACKSMITH."-"P. A. F., Rugby" writes:-" Thanks to our harmonious friend for his extract from non-historic times' on ancient architectural remains in India,' but why did he not give us the source from whence he drew his ideas? unless the "H. B." is in reality either Sir John Lub. bock or the Quarterly Reviewer' in disguise." [Possibly the "H. B." is the latter.] THE PEDESPEDE.-S. F. Shakespeare, of Thrapstone, says "I see your remarks in the MECHANIC of May 6th, inst,, about the pedespede invention. I regret you seem doubtful, and appear to think it must be hurtful to any one using them. I, however, beg to assure you this is not the case. By the appliances I make use of in those I constructed, no danger would arise, whilst every comfort is allowed for the person using them, as he is able to use his feet and ankles easily, the same as during skating on the ice." ALGEBRA.-"T. J. O'C." observes: - "Since almost every arithmetical solution which appears in the pages of our valuable journal is solved by means of algebra, and knowing that there are several brother readers complete masters of this beautiful science, I hope that soine of them will lend his help"g-hand during his leisure moments, and confer on his brother readers a short discourse on this valuable science." THE "PHANTOM" VELOCE.-The following are extracts from letters just received:-"I wish Mr. E. M. T. Tydeman lived in my neighbourhood (Marlborough), to mount my Phautom just once. He would then be convinced that he has made a great mistake in speaking against the 'Phantom' with rubber tires, as certainly there is no comparison with ordinary wheels. The nearest I can compare is riding in a broad-wheeled waggon full trot and the riding in a carriage."-G. JONES.-Mr. St. John T. Gore, of Eaton Place, Guernsey, says: "Having noticed a letter from Mr. G. Sykes, of Huddersfield, relative to the Phantom, wheel, as made by the Phantom Wheel Company, I think it only fair (especially after a letter from a Mr. Tydeman that appeared in your paper some little time since) to state that having tried a pair of the above wheels, with india-rubber tires, in my bicycle, for the last three weeks, I can fully endorse Mr. Sykes' statements concerning them in every particular, with the exception; perhaps of the weight, although they are undoubtedly lighter than many bicycle wheels."-G. S. Cole, Sea Side, Llanelly, says: Having the front wheel of my bicycle broken, I sent for one of the rubber-tiered Phantom' wheels, with axle, cranks and pedals complete; and I am of the same opinion as Mr. Sturges, of Huddersfield, respecting it; and I may add that several from the town and neigbourhood have sent, and are about sendLancaster," says:-"I have tried the] hantom veloce wheel, and find it much superior to the ordinary wheel, and fully endorse Mr. Sykes's senti The best wire for primary would be No. 12 cotton. description given by Messrs. Turner of their lubrica. ing for the same. "C. H. Maxsted, of Ca-t'e Park, Two layers of this would be sufficient, taking nearly 51b. for the two. If he used a thinner wire, he would have to use more layers to magnetise the core to the same extent with a given battery power. In addition to G. P. tissue, I find paper soaked in melted paraffin an excellent insulating material. Unsized newspaper is the most preferable for this. I hope these will be the suggestions he asks for; being based on experience, I am sure of their correctness. A. E. TUCKER. THE EARTH'S FIGURE AND ROTATION. SIR,-Now that Mr. Beardsley has so kindly come forward to put us right upon the above subjects, I think we must not let him go without getting an explanation of all the appearances, celestial and otherwise, which are commonly said to result from the facts that the earth does rotate, and is of a round shape. For example, the shadow thrown on the moon in an eclipse, the fact of circumnavigation having been effected, coupled with the circumstance that ships are a day out in their reckoning of the time, one way or another, according to the direction in which the voyage is performed, and several other little circumstances which we must not fail to put him in mind of. It is rather too bad to expect such men as Mr. Proctor to waste time and trouble about such matters; it is like getting a professor of six or seven languages to argue with a precocious juvenile who insists that the alphabet is all wrong because the letter O is made round instead of I admire Mr. Beardsley's diagram of the sun's apparent diurnal motion, but can't make out how he brings the sun back so as to start all right in the morning. But this is an "error of vision "on my square. part, no doubt. You see I do not argue on the subjects I mention above. because they are in every book on Natural Philosophy, and do not therefore require repetition. I will undertake to find Mr. Beardsley in things to explain-and some uncomfortable things, toowhich he will find not so easy as he thinks, judging by the style of his letters. To my eye the roundness of a dew-drop is quite sufficient proof of the shape of the earth, considering who was the Architect of both. Mr. Beardsley says he does not hold that the earth is a vast plane. If not a plane, and not a sphere, what shape Sack-bag shape, perhaps, which is neither is she? round, square, nor oval, as I once heard. He ought at least to let us know what shape she really is, as otherwise some nervous individuals may fear to go out after dark, as they will fancy every bank to be an edge over which they may tumble into space. H. G, Salop. THE MOA OR DINORNIS. SIP, I am glad to see "Urban" has returned to the ranks of "our" correspond ents, and note his re TURNER'S ENGINE LUBRICATOR. For the information of my brother engineers, I can The find it was illustrated in our ENGLISH MECHANIC of ENGINEER. EXTRACTS FROM CORRESPONDENCE. COMMERCE AND TRADE.-" Herbert says:the sum of the imports into the United Kingdom for "In answer to the query of Saul Rymea,' who quotes 1868 as £294,693,608, and the exports as £179,677,812, I say that those figures indicate a very lucrative me £18,000, and she brings me back a cargo in lieu of trade. If I freight a ship with a cargo which costs it, of the value of £29,000, I think my trade would be very prosperous.' Now, if I individually should prosper doing a trade giving such returns, so does the nation of which I form an unit. STAINING OAK.-" Faber" writes:-"Some time ago one of your correspondents asked the above ques ments. REPLIES TO QUERIES. [2007.] TEMPERING DRILLS. Once more! "Tis a pity S. T." should pass unanswered, since he took so much pains to get off the printer's shoulders, where he was so considerately placed by "J. B." Steel is hardened by being heated to redness and then quenched suddenly in some cold fluid. Tempering is not hardening, as" S. T." affirms in the sentence led off by that word, page 129, but a means of reducing the brittleness of hardened steel. which unhappily cannot be performed without reducing also the degree of hardness. Annealing either hardened or soft steel consists in beating to redness and allowing it slowly to cool; the effect of which in the case of soft steel is rather doubtful, unless performed in charcoal dust. If "S. T." can either harden or temper by the process bearing his signature, which we have in good set terms and black and white at page 19-namely, “Heat your drill to a dull red, allow it slowly to cool," &c., we can also give him credit for being able to shut his eyes by holding his breath. At any rate, if he will not see now that he is, to say the least, confounding two different things, he is shutting his eyes with a vengeance somehow or other. The whole of his notice how correspondents, when set right, bed, by world but making a rope of sand. It is curious to "reply to the criticisms of J. B.'" is nothing in the once if they feel themselves equivocally placed, by assuming the circumlocutive style-NOBODY. [2374.)-BREWING.-"New Subscriber "begs to thank A Reader of Old Books" and "W. L." for their information. He has just received a very elaborate work, but shall bear "W. L." in mind. [2402.]-ELECTRIC BELLS AND BATTERIESIf A. Spencer winds his coils with about 3oz. of No. cells of sulphate of lead battery, as descrbed by mo 28 silk-covered wire, and uses 2 cells of manganese, or in the same number of our MECHANIC as that in which his query appears he will find his bell will ring furiously.-A GOOD BOY. 3 [2522]-SHEET IRON RUDDER.-Some people are not content with having a canoe with as few appurtenances as possible, but invariably endeavour to convert it into a floating lumber shop, carrying two masts instead of one, which is quite sufficient if there is anything fit to be called a sail for it; a jib which is no use, a boat-hook, or shoving pole, creep, cable, cook |