[1081] I INCLOSE you drawing and description of an apparatus for preventing priming into cylinders which has been in operation for the last two years on board the steam-tug Ariel, and has given such satisfaction that the owners, Messrs. Page & East, of Nine Elms, Battersea, have paten The description is as follows:-A, steam chest of boiler; B, short cast-iron cylinder bolted on ditto. To the cover of this cylinder are attached the three perforated copper cylinders C, D and E; F, steam-pipe leading to engine; G, pipe leading to bottom of boiler; H, perforated plate. The action of the apparatus can be easily understood by reference to the drawing. The steam first enters through the perforated plate H and follows the direction of the arrows through the perforated cylinders C, D, and E to the steam-pipe F, the mud and water by its own specific gravity passing down the pipe G. The boiler is multitubular, of the ordinary highpressure type; diameter of shell, 6ft. 8in.; length of do., 9ft. 4in.; with single furnace, 3ft. 8in. diameter; working pressure, 50lb. per square inch. ARIEL. [1032] IT appears to me that E. Malbon (let. 991) has been arguing his point on totally false grounds. I cannot go into his arguments fully, but will take one or two leading points. Valve; D, Gauge Tube; F, Condensing Tubes; G,Orifice great deal of worry of mind if they were enabled to | are attended to, far more startling effects may be pro : structed as to descend, say a fin., with any required A TELL-TALE OMNIBUS STEP.-A step is so conHe states that there is three times the heat diffused indicating that a passenger has entered; ringing a bell weight. This fall causes a movement of wheelwork, on a boiler plate if the pressure is increased from 71b. also by the driver's side. to 211b. I find the temperature of 71b. steam is ing will perform the same operation, so that at the 234°, and of 211b. 262°, a difference of 28° only. A passenger on descend also states that if the pressure is increased to 21lb. the must be taken for the number carried. He end of the day or journey half the number marked current of steam is increased in speed. This is by no means necessary, as it is quite possible, and also pro- constructed to show the time during which the step the step being wedged or fastened, the tell-tale may be To prevent bable that the engine will be worked at the same speed, was pressed down; to keep it wedged up may be renand therefore the cylinder full of steam taken at the dered impossible by the overlapping of the inclosing box. same intervals as before. In fact, his own argument requires that it shall be so, as an means also an increase of power beyond that owing to increase of speed the extra steam pressure. I believe that it is also pretty well known that the disturbance and ebullition is no greater in high than in low pressure boilers for an equal bulk of steam supplied, and therefore his argument of extra disturbance cannot be considered. The thing which would cause the boiler to prime would be running the piston at a higher speed, and using a greater bulk of steam. T. F. REFRACTION. [1033] "F.R.A.S." explains the matter just as I understand it, but I cannot reconcile the explanation with my books-Darby and Loomis. statement is taken bodily out of Loomis, I will quote As Darby's the latter. In giving rules for the adjustments of the equatorial, he directs, first:-"Observe the polar distance of any known star, then turning the polar axis half round observe it again; take the mean of the two; correct for refraction; compare with the true N.P.D. in Nautical Almanac, &c." But how correct or refraction? Well, he gives an example:-"When Ursa Min. was near the meridian its N.P.D. was observed to be 7° 44' 7", the face of the declination circle being west, and 7° 44' 40' when the circle was cast. The mean is 7° 44' 235; the refraction was 52" 8, making the corrected P.D. 7° 43′ 30" 7," and so on. Plainly he corrects for refraction by subtracting from the observed N.P.D., and I confess I am puzzled. GRATIS INVENTIONS. BEGINNER. [1034] MAN has been somewhere defined as a toolmaking animal; nothing seems to delight him so much as a new tool, and the amount of inventive talent lost to the world through want of money, opportunity, and practical knowledge, I believe to be enormous. Hoping that I may not be accused of adding the last straw to the camel's back, I venture to propose that you should encourage those of your subscribers who possess, or think they possess, inventive powers, to make known their suggestions in a column in your paper, subject of course, as all contributions must be, to your right of rejection. This column might be headed, Publico." There are many who might be spared a "Pro Bono in your paper, so that his invention, if adopted, might At present if a dozen invent the same thing at the M. PARIS. HYDRO-ELECTRIC MACHINE. pressure gauge, water gauge, and safety-valve, loaded to PATENT COMPOSITION GRINDING-WHEEL. [1036] I FORWARD you a sketch of a very useful tool Fig. 1 is an apparatus to be screwed to the slide-rest, forthe lathe, which may be of service to our readers. mounted on a spindle as shown in the inclosed sketch. It consists of a patent composition grinding-wheel, and driven from the overhead motion. Fig. 2 has s surfacing inside of cylinders, &c., and Fig. 3, is a either wet or dry, and are not liable to break when "FLIES IN LIQUOR" AND FLEAS IN WATER makes some remarks with reference to an article which on the look-out were instructed to put the capture in a specimen-tube, which was labelled accordingly. Now it so happened that one or two captures were made, but I was unable to prepare them for mounting, so they were left to themselves, which lasted for the space of about twelve weeks, confined in a foz. specimen tube closely corked. I amused myself during that time by occasionally examining my collection, and noticed the remarkably tenacious power which the flea possesses over its life. I thought I would learn whether they have the same power when immersed in water. Another experiment, made several years age, was with an insect known as the common Black Cocktail, which consisted in endeavouring to kill it by keeping it in a bottle of carbonic acid gas, but it would not die. I then tried the effects of keeping a continual supply of fresh gas pouring in the bottle in which it was confined. By this treatment it showed symptoms of great uneasiness, and it was only after a prolonged immersion in this gas that Mr. Cocktail succumbed to the enemy. Lastly, if any one doubts the above statements, let him put them to the test, and report the results. THOS. HARDING. BOULT'S MOULDING, CARVING, AND PANELLING [1038] I CUT from the Scientific American a drawing and description of a machine. This machine, of which Fig. 1 is a perspective view, is designed for moulding irregular forms and panels upon surfaces in the manufacture of furniture, cars, organs, buildings, &c. By reference to Fig. 1 will be seen a guide point, A, suspended over the cutter B, whose centres are in line with each other. The guide point is vertically adjusted by a screw wheel C. The cutter B is attached to the spindle D, which obtains its motion from the belt on primary shaft E. A form or template is prepared, as shown in No. 1, Fig. 4, and is attached to No. 2, on the side opposite to where the cutting is to be done. The piece is placed under the guide point, which is then lowered to the pattern. The cutter being, when not in use, below the table, is now brought up by pressing the foot upon the lever F, Fig. 1, connecting with the bridgetree G, to the desired height, which is regulated by the adjusting rod H. These means govern the depth to which the cutters penetrate. The form is then moved around against the guide point, and its shape and design transferred to the piece worked, as at No. 2, Fig. 4. Any number of designs may be cut without change of machinery. The cutter N is held in the chuck M, | Mr. Davis tells us were for students who had passed Moulding brackets of fret-work is done, as shown at Fig. 5. A spindle head is placed upon the arched arm S, Fig. 2. The spindle is driven by a belt passing over pulleys T, from the primary shaft, heretofore described. For this work the double-stem cutter, shown in Fig. 3, at L, is employed, with which the smallest openings may be moulded. An adjustable table is placed upon the bed, and the double stem-cutter adapted to the work is inserted in the spindle by which any style of fretwork may be executed. ΚΑΡΡΑ. CHEMICAL.-MR. R. E. GOFFIN AND MR. G. E. I am almost ashamed again to refer to the poor word radical, as I am afraid Mr. Davis's knowledge of language is not so good as his knowledge of chemistry. He asks, What has radical to do with radicle? That is just what I wish to know; he has made one stand for the other. Radicle may be put in this form :Latin-Radix. Radicula. English-Root. Little root, radicle. Particle follows the same form, particle = Latin particula, but article does not; there is no articula but Latin-Artus. Articulus. Little limb, article. Articuloris. jective abstract, to which radix is concrete, and by Radical, I again repeat, is a class designation; an adanalogy takes the form radicalis. Mr. Davis, in his characteristic manner, says, "Radical comes from radicalis it is true." I never said so. So far as I am aware radicalis does not exist, [1039] I was rather surprised at Mr. Davis's first reply to me, and I feel more so at his second. Mr. Davis compels me to use the old adage, "None so blind as those who won't see." At first, I was unable to understand for what class of readers Mr. Davis was writing, as the articles appeared very much like what in geology is termed conglomerate; Mr. Davis, however, soon settled the point by informing us that they were intended for an advanced class. He now says, "Mr. Goffin seems to have a notion that a treatise ought to be written either for an elementary student or an advanced one." Exactly so. He has for once understood me, except that I not only have a notion, but a very decided opinion on the subject, and the real but radical is formed as if it did, following the analogy value of Mr. Davis's chapters, so far as they serve either purpose, may be summed up as follows:-To the elementary student, very little; to the advanced, little; to the general reader, less; and all this for want of a system, not for subject. Mr. Davis has drawn from reliable sources, hence few chemical errors. He has not ventured from his stronghold, but see how slightingly he speaks of Professor Roscoe. The chapters Formulis, Formal (Eng.). of such formations, as:- P.S.-I have opened my letter to say that I have just seen the erratum in Mr. Davis's last letter, noticed in your number of December 9, hence what I have said about articula does not reflect on Mr. Davis. [In intimating the desirability that this controversy between Mr. Goffin and Mr. Davis should here terminate, we think it right to say that Mr. Davis commeneed his series of articles with the intention of considerably extending it; but being informed that we intended in future to discourage long series of articles on any subject, Mr. Davis complied with our request, and accommodated the treatment of the subject to the limited space afforded him.-ED.] CLAY RETORTS. [1040] I SEE that a discussion as to the deposition of carbon in gas retorts has lately been opened in your columns, and I therefore send you my ideas on the subject, which, if right, will I hope instruct others, and if wrong, be the means of obtaining information from those who have a more extended knowledge of the subject than myself. One cannot speak of minutise in this subject without first going through the generalities of the case, so I will first treat of the different forms in which clay retorts are constructed, as that has a vast deal to do with their working foul or clean. I think a 16in. retort ample; not being inconveniently large, it has yet sufficient surface to work off a 2-cwt. charge in an efficient manner, which weight is quite as much as a retort ought to carry when in good heat. pro For general purposes there is no form extant that will act better than the shape, for the reasons that it has a flat bottom, so that the coals, being evenly laid, receive the heat uniformly, which is one of the chief desiderata. The arched top is the best form for equal radiation and uninterrupted passage for the ducts of distillation, which combined with the beforementioned advantages of level bed for the coal, makes it, in my own opinion, the best working form of any in use. The ear-shaped retorts, although they may claim that the concave bottom arrests the heat of the furnace, have the great defect that the sharp angles at the bottom corners inside soon get so foul and choked with carbon as to render them virtually D shaped, only with the disadvantage of such a thickness of carbon, which is a very bad conductor, as to more than counteract any advantage the outside may possess. Round retorts act very well in some cases, and from their form are very strong, but they also have the same drawbacks as the ear-shaped, although in a much lesser degree; the carbon of course fouls them, but I find in practice that a D retort will make as much carbon as a round-in fact, there is not much difference in this respect, what there is is more owing to difference of temperature than form, as the hotter a retort is the faster it carbonizes coal, and, therefore, the more carbon it will accumulate; were the retorts worked cool, the carbon deposit would be very slight indeed, but then the yield would be also very small. Some of the richest of the gas is left behind in the retort in the form of graphite, owing to the high temperature seizing and decomposing it by depositing the carbon, and liberating the hydrogen that was combined with it. Therefore it stands to reason that the longer the gas remains in the retort after it has been evolved, the more its hydrocarbon will be decomposed by the heat, and carbon deposited; or, in other words, the less back-pressure there is, the better in every respect, both as regards prevention of leakage and retention of vola tile constituents-hence the vast benefit to be derived from an exhauster properly worked. Then again, from the same cause the charge ought not to remain in the retort longer than is absolutely necessary for carbonization, as after the illuminators have been evolved, the residue is very injurious to the gas, consisting of sulphuric compounds, so that although a higher rate may be got out by long carbonization, yet the purifiers have to pay dear for it afterwards. For the same reason I may complain of a defect in round retorts, the coal is not on a level surface, being, of course, thick in the middle and tapering off at the sides; therefore the surface and thinner parts carbonize first, and a cake of carbonized coke forms over the still unconsumed part of the charge in the middle, so that the bottom and middle have to struggle through a strainer, if I may use the word, of decomposing material, which robs it of its richness, and therefore is thick, and so increase the weight of the retort and, by The use of coal, wet or dry, does not influence the A certain proportion of carbon that penetrates into ANALYSIS.-ETHYLENE.-PLATINUM AND [1041] As long as "Un Irlandais," query 5795, turns. It is absolutely necessary, to obtain correct Another point I may remark on, is that it is neces- C2H5 0+ H2SO4 = C2H1 + H2O + H2SO4. As a matter of fact, though, a number of secondary and the lower bass strings at about 1-9th or 1-10th of ORGAN PIPES. [1048] IN reading "Adept's" communication on metal pipe-making, it struck me that he has not called the attention of the amateur to the most important job in the whole process, viz., the care and skill required in uniting the body" to the "foot" perpendicularly. I have worked in one of the largest organ factories in England, and I found it the most difficult of all metal Unless pipes are put together properly they work. would be all over the organ at the top, some leaning one way, and some another, besides the room they would take up. J. J. HARTLEY. THE ORGAN.-FROM "AN ADEPT." [1044] I FIND I have accidentally overlooked a letter addressed to me by our excellent friend "The Harmo nious Blacksmith," and now wish to express my entire concurrence in what he has written, or to say "ditto" to him, as he facetiously terms it. I purpose including the description of an arrange ment somewhat after the system he proposes in the next section of my subject, but I shall be unavoidably absent for the next few weeks. In reply to the observations of "Pipemaker," on in a great part an answer to them, but it may probably page 303, I may observe that my last communication is be well to remark that my aim has been only to describe where pipe construction differs from ordinary soldering, as I presume no one would attempt to make a pipe who could not, as I have expressed it, "handle the soldering-iron properly," which sentence I intended to include the minor details of the operation. With all courtesy, I beg to differ from your corre spondent's recommendation of the abominable" board," with which I am well acquainted, and a most greasefilthy, dirty affair it is; my hollowed tile, as described, answering the same purpose, and being far superior in matter of individual opinion, and I also prefer my every respect; but this is, as I have before remarked, own plan of preparing the edges of the metal, which is likewise a question of a similar kind. AN ADEPT. acid he refers to, and can also use "methylated spirit," a would obtain about a pound and a half of sulphate of "St. Clarette" (query 5914) asks for the very answer by the dozen. monious Blacksmith" (let. 952, p. 281), will have to MUSICAL STRINGS. URBAN. REED ORGANS AND HARMONIUMS. [1045] WE have read with interest several communications in the ENGLISH MECHANIC respecting reed organs and harmoniums, and now write thinking we may be able to give some items of interest to your readers, but especially to correct one or two errors into which your correspondent, Mr. Hermaan Smith, has fallen, in his communication (let. 753) entitled "Ameri can Organs one-half of an Accordion." Perhaps, being Americans, we are actuated by a desire to claim at least all the glory that belongs to us. Mr. Smith says: "The accordion is said to have been invented about the year 1825, and numbers found their way to America;" that "the earliest accordions were of single action only, but up to 1835 great improvements were made;" and he evidently supposes that the American instruments were taken from these accordions. The fact is, that reed instruments, as a class, whether employing force of suction bellows, are an American invention, and instead of the organs and harmoniums being taken from the accordions, it is probable that the latter instrument was taken from the former. We have in our possession the ENGLISH MECHANIC No. 296, he had better" step- November 11, 1818 (and duly signed by the President, [1042] IF the inquirer, No. 5905, does not possess the original patent granted by the United States, a source of expense rather than profit, as of course anfetchit" without delay, for in it are several scales James Munroe; Secretary of State, John Quincey what it loses has to be made up in the other retorts. of pianoforte strings, in some of which the distances Adams; and Attorney-General, William Wirt), to I have been chiefly in the habit of working tube from the bridge at which the hammers strike are retorts, open at both ends, and like the plau very much, specified. He will see that distance is not limited to for a new and useful improvement in organs, which is "Aaron Merrill Peasley, a citizen of the United States," as it seems to utilize as much heat as can possibly be 2.15ths and a minute fraction (which would approxi- described as consisting in substituting in place appropriated. I find the carbon will be accumulated mate to 4th), but may be varied advantageously to a very of the pipes, usually called reed-pipes, a plate of most plentifully about the middle, where the two scoops considerable extent. meet and the coal is thinnest, but we have no difficulty once told me you must strike at the harmonic-by the number of holes of suitable form, in each of An experienced manufacturer metal, or any other fit substance in which are a in removing it by not charging the retort for a turn and way he did not specify which harmonic, their name is which is fitted a piece of brass or other elastic then chipping it off; it is the contraction of the sur-legion and if you don't strike at 4th you must strike at substance, capable of vibrating so as to produce a face caused by the cold air that canses it to loosen, and 4th. He omitted to say why, probably not having a very tone." These are to be made to vibrate either he strong reason for the faith which was in him, which force or snction bellows, though the inventor says he faith he acknowledged was founded on mere hearsay. prefers the latter. As the United States Government The fact is that there is no rule whatever. For then, as now, granted patents only for new things oristrings of ordinary thickness, like those in the scales ginated here, and made careful examination to ascer Nos. 1, 2, and 3, it is usual to cause the hammers to fain if anything for which a patent was asked had been strike at from 1-16th to 1-12th of their length at the used or known before, and as the description is at once top of the compass, at about th or 1-7th at middle C so explicit and general as to cover all reed instruments, then it easily comes of. I forgot to mention, when talking of dimensions at the beginning of my letter, that I think 3 inches ample thickness for any clay retort; less would render it dangerously weak, and more would interrupt too much heat. Some engineers lay an objection to the D shape, on the ground that the bottom angles are necessarily it is fair to suppose that this is an American invention. Attention is asked to the fact that Mr. Peasley styled his invention au improvement in "organs," and that thus the name organ is the original one for instruments of the class. This tends to justify our return to this name about ten years since, a course in which we have been followed by American makers generally. But better reasons for this name are, that it is descriptive, convenient, appropriate, and unobjectionable. If the barrel-organ be allowed its name, why not cabinet organ? At least the responsibility for change rests with European makers not with us. As respects the question of suction or force bellows, we have only to say that we use the former because we have found it impossible to produce tones of as good quality with the other. Yet it is a mistake, as many can testify, to suppose that the mere employment of a suction bellows secures the best quality of tone. One who will test the matter with an accordion will not find such very great difference in the qualities of tone, when the air is forced or drawn through the reeds. The suction bellows renders possible certain other arrangements and conditions which experience proves essential for greatest excellence, and so is itself a necessity. Others may know how to produce tones of the best quality without it; we do not. A fact indicating the comparative value of suction or force, is that in America, where both have been tried, and where European instruments were at one time largely imported, all makers have now adopted the suction bellows, and instead of getting instruments of this class from other countries, we now export largely to them. Let us not be understood that this change is owing entirely to this difference in construction. There are others of equal or more importance, but the suction bellows seems to be a starting-point. After it has been adopted, it will be found that there is still a great way to go before greatest excellence in results is obtained. The making of reed instruments is something like that of violins. It is easy to make poor ones; very difficult to make the best; and certain differences, which cannot be defined by any rules, and which are so small that it seems impossible they can have any perceptible effect, are yet very important. Your correspondents are right (we think) in supposing it impossible to obtain so great variety with a suction bellows as with a force; but are not a moderate number of good effects more desirable than any num ber of bad ones? We do not notice Mr. Smith's criticisms on some features of our cabinet organs, because, as he frankly confesses he never heard one, it would hardly be reasonable to expect correct judgment of them from him. We are confident he is as much in error in supposing the automatic swell was employed on harmoniums thirty years since, as he evidently is as to the effects of this swell. It has not indeed all the same effects which a skilled player (he must have much skill) can obtain from the expressive swell of the harmonium, but it is capable of many of the same, with others more valuable, and does not require a tenth of the skill for its efficient use. We may retort by mentioning the fact that though we employed the expressive swell many years since, we have now almost entirely discarded it, finding the automatic so much better. Will you good-naturedly permit some of mother England's "smart" children to have a little fun with the old lady, by saying that it strikes us as rather comical, and very English, that one should seriously attempt to criticise, compare, and judge a musical in strument which he never heard? MASON AND HAMLIN. Boston and New York, U.S.A., Nov. 28, 1870. THE HARMONIUM AND THE HUMAN VOICE. [1046] THE analogy so ingeniously propounded by Mr. Hermann Smithi, as existing between the several component parts of what may be called the voice of the harmonium and those of the human voice, is admissible to the extent that each possesses in structure the counterpart of the other; but to this extent only. A little examination shows a great and fundamental difference between them. The harmonium has a free reed, actuat d by a comparatively low pressure of wind; the human larynx has a double "beating" reed, vibrated by a very high pressure of wind, and would be the most powerful of wind instruments, but for the tubes of "angmentation" or "re-inforcement" possessed by those instruments which are variously made in imitation of it, such as the hautbois, bassoon, and instruments of the trumpet class; the latter forming the best imitation, inasmuch as the lips, both by their structure and action, most closely resemble those of the chord vocales of the human larynx. I venture to draw the attention of Mr. Smith (as well as of those interested in the subject) to the foregoing observations, not for the purpose of endeavouring to subvert his theory, but to suggest the desirability of enlarging upon it and carrying it to its obvious conclusion. Many years ago I heard the musical effects of an artificial larynx, in which the vocal cords were formed of india-rubber, and I must confess that the sounds produced were suggestive rather of bovine than of human agency; still, the human voice is but a mechanical effect, and it would not seem unreasonable to anticipate that, by a closer imitation of the human instrument, the harmonium might, in the hands of science and art, become possessed of a capability of producing a real vox humans. G. E. N. HOW TO MAKE A GOOD PRINTING PRESS. [1047] THE press invented by A. Wilkinson (let. 916, p. 278) is in many respects similar to one I had occasion to find fault with some time ago. As is usual in amateur attempts of this kind, the pressure is ap. plied in an incorrect manner. The principle adopted in this case is that of the lithographic press-but with a difference. No letterpress printing, fit to look at, can be done by a rolling, scraping pressure. If a cy linder must be employed, the sheet should be carried on it, and so pressed on the type. However, Mr. Wilkinson may vastly improve his press by mounting the bearings of his roller on thick vulcanized rubber, or by applying springs in a manner that will allow the roller to yield a trifle (vide p. 584, Vol X.). Instead of covering his tympan with two thicknesses of cotton, let him try the usual feltlike blanket or parchment. It would be better to make the tympan double - that is, with an inner frame, as then he could place sheets of paper or blanket between, and so obtain a better impression. A type-high bearer placed at each end of the forme will also help him, as it may prevent the cylinder falling with too great force on the edge of the type. Instead of fastening the sheet on with pins, it would be an improvement to use "points "-thin slips of iron, with a small steel point, fitted in at right angles at one end-which are screwed to the tympanframe and fall into the folds of the paper (or spaces between the pages) as shown in his engraving. Of course, if only one page is to be "worked," they might be made to hold the sheet at the sides or ends. If Mr. Wilkinson can "work 500 impressions per hour," inking the forme himself, either he is a remarkably expert workman, or his press is a wonderful improvement on those antiquated implements used in the best London offices, secing that it is considered good work if two men produce a "trifle" under 500 impressions per hour between them-i. e., one to ink and one to pull. Surely some of our readers can invent a useful little press; but they must bear in mind that the power should be applied in a perpendicular direction, or the roller, cylinder, or "what not," should carry the sheet and press it on the type. SAUL RYMEA. TURNING SHORT SCREWS. the usual course in works of this kind, but would like [1048] I THINK "G. F. O." (let. 917) has followed to ask him one question thereon. Did "G. F. O." test the truth of the surfaces "a" and "b" after the rings were chucked, and before commencing to cut the screws? I think not: for if he had, he would probably have found one of them "run out" by about 1-100in. This might possibly be caused by his having omitted to see, first, whether, the bottom of his chuck was true or not; and secondly, if true, that the ring was seated on the bottom all round. The remedy seems to me to be this; to re-chuck each ring in a true chuck, and then take a slight scrape off the faulty place. When this has been done, I think he will find the rings come exactly together. No. 170. GRIP CHUCK. [1049] I BEG to thank "J. K. P." for the opinion he has given (let. 954), and also for pointing out the whereabouts of "W. T. C.'s" criticism. I looked all through the volume, thinking I had seen it somewhere, but expected to find it over "J. K. P.'s" initials, and of course looked in vain. My idea of a grip chuck was derived from that of a parallel vice, the jaws of which might be made to move to and from the centre by screws, the same as those of a four-jaw chuck; and "Virginian's" sketch was the only one at all approaching that description; it is also the only one which admits of the use of wood jaws to avoid bruising partially finished work. I think "J. K. P." had in his mind's eye the fourjaw chuck as a standard of excellence, and for metal turning, with back-geared lathe and metal speeds, it deserves, no doubt, all that can be said in its praise. At wood turning speeds, however, I fear so heavy a chuck would overload the mandrel, and make it sluggish and heavy to drive. Hence arises my desire to dispense with, say, one-half the weight, by removing two of the jaws, if this can be done without taking from the chuck's usefulness. Again, the power of helding work out of centre would seem to be limited in use at high speeds, owing to the oscillation thereby occasioned; and the question arises whether this power or that of self-centreing (for which I confess a small amount of amateur's weakness) would be most useful at the speeds mentioned. ON TELESCOPES. No. 170. [1050] I HAVE been very much interested in the articles on telescopes which have appeared in the ENGLISH MECHANIC, commencing with the instructions of "Arcturus." I am in want of a good reflecting telescope of 6 or 8in. aperture, and was thinking if I could get a good speculum, with diagonal mirror and eyepieces, I might be able for about £15 to get a good one by mounting it myself. I may state that I have a 5in. centre slide and screw-cutting lathe. Mr. Browning, though giving the prices of specula in his "Plea for Reflectors," declines to sell unmounted specula. Can any of your readers give me any information respecting the performance of specula made by Mr. Purkiss? Mr. Browning says of Saturn, in his "Plea" that the 6in. speculum will show four satel lites, and the 8 in. six satellites; and he further adds that he considers that in light-grasping power the reflector is equal to an achromatic one-sixth less in diameter and in dividing power to the finest achromatics of the same aperture. How am I to judge between the foregoing statement and the following by the Rev. T. W. Webb, in his "Celestial Objects," p. 154 ? Speaking of achromatics and Saturn's satellites, he says that 3 or 4in. aperture may be expected to show them all. My object in writing to you is to get the best information I can on the telescope, and I shall be much obliged if some one will inform me the best way to get a good telescope, either a reflector or refractor. INQUIRER. [1051] I SHALL ask your kind permission to say a few words on the telescope generally, and first I must really take up the cudgels in defence of short-focus instruments. I know F.R.A.S." will not think it unreasonable if I dissent from his opinion expressed in let. 910, but will rather feel glad that both sides of the question should get a fair hearing. There seem to me, then, many and great advantages arising from shortness of focal length, not the least of which is the comfort and convenience attending it. Any one who has used a 4in: achromatic of 7ft. focus, and tried to do some really practical work with it, will comprehend the pleasure I felt when I had disposed of it and obtained a 4in. of 5ft. focus. There is less moving about, greater portability, much lighter weight and this last consideration is of very great importance when the instrument is equatorially mounted,-every inch cut off the focus amounts to some pounds weight less in the mounting, and some pounds less out of the pocket; if an observatory is built, there is considerable expense saved also. But apart from these considerations, which do not affect the optical performance of the instrument, except in so far as its steadiness is concerned, there is another consideration of far greater importance. The light-grasping power of the objective is proportionally increased as the focal length is shortened and the field of view enlarged. To prove this, it is only necessary to compare (as I have done most carefully) a 2in. object-glass of 8ft. focus with a similar aperture of only 2ft. focus, The difference in the above-mentioned particulars is most strikingly brought out. Perhaps some of your readers have examined one of Dallmeyer's terrestrial telescopes of 2in. aperture and about 18in. focus; if so, they will image, large field of view, and beautiful definition, bear me out in what I have said. For brightness of they cannot be surpassed. It is only a pity Mr. Dallmeyer has not applied the same principles to his astronomical telescopes, and reduced their focus by some diameters of their aperture. His Cin. objectglass has the long focus of Sft., while that of Cooke & Sons, for the same aperture, is only 7ft. 6in.-a very considerable saving of room and weight. But, somebody says, the spherical aberration cannot be well corrected unless you make the focal length 16 diameters at least of the aperture. Surely, this is setting ourselves against progress. Is it not a fact that opticians now find themselves able to give an elliptic, parabolic, or hyperbolic curve to a spherical glass surface, or could not the spherical aberration be cured in this way, when it could not be corrected by spherical curves? I have a "With Browning" mirror of 4in. aperture, of only 30in. focus, so beautifully parabolized that it is almost absolutely perfect. A similar treatment of the surfaces of a compound objectglass would insure perfect immunity from this troublesome cause of indistinctness, while the focus was considerably shortened. Some opticians, I am glad to say, have not failed to avail themselves of this new power; amongst them Mr. Grubb, of Dublin. He, I am informed, has applied this principle to the correction of several large objectglasses-notably to the magnificent 18in. refractor recently presented by the Royal Society to Mr. Huggins for spectroscopic work, the definition of which is reported to be very good. I have seen also somewhere that Cooke & Sons have applied the same principle in the formation of the gigantic object-glass, 25in. diameter, equatorially mounted, for Mr. Newall, with very good effect. By a proper balancing of the refractive indices of the flint and crown glass, or by using this method for the correction of spherical aberration, I cannot see why the focal length of refractors might not be considerably reduced (to 10 or at most 12 dia. meters), to the great comfort and convenience of astronomers. The use of deep eyepieces has also been brought as an objection against shortness of focus, but this should not stand in the way, for with the rapid advancement of microscopic science such powers as 1-6th, 1-8th, 1-10th of an inch are mere child's play, and can be as perfectly corrected as those of larger focus. I have heard that Mr. Grubb has recently constructed cemented object-glasses of very short focus (10 diameters, I think), and that they succeeded admirably. I have not learned the particulars, but perhaps may do so, and shall let your readers know, should they wish it. The wonderful improvement in optical glass which has taken place of late years, its beautiful transparency, uniform quality, and absence of colour, should spur on the opticians towards the attainment of this end. It is most remarkable how much more light passes through a modern objective to what was transmitted through an old one of similar aperture. Whether from the colour of the glass in the old objectives, or want of limpidity and fine polish, I think it may be said without fear of contradiction, that an object-glass of the present day, by a good maker, would bear favourable comparison in light-grasping power to one made some 30 or 40 years ago, of nearly an inch larger aperture. Dr. Robinson, of Armagh, Ireland, contributed a very interesting paper on this subject to the Royal Society, an extract from which appears in the Proceedings of that body for last year. He mentions (as well as I can remember) having tested, by Zöllner's photometer, a number of object-glasses in his possession, with the following results (I quote from memory): An object-glass by Dollond of 2.75 aperture, and one by Tulley, of about 8in., and that neither of these transmitted as much light as would be reflected from a metal speculum. Another by Tulley, made expressly for the observatory, and a larger one by Cauchroix, of Paris, barely a fraction more light. But when he came to examine the more modern ones, by Fraünhofer, Cooke & Son, and Grubb, there was a most striking and remarkable advance in light-transmitting power. The large object-glass of 12in. aperture, constructed by Grubb for the observatory, the inner surfaces of which are cemented, was remarkable in this respect, transmitting very nearly 900 for every 1,000 rays which fell upon it, and proving, beyond all question, the vast improvement and advance which Chance had made in the manufacturing of limpid glass discs. startling impression which the size and clearly-marked lever, connects it to the lower part of the upright outline of the great ball left upon my mind. Those wooden palley, the cord being kept tight by a weight on readers of your journal who seem anxious to maintain the lower end. Another cord connects the upper part the credit of their "cheap astronomical telescopes," of the pulley to the lathe mandrel. Before looping would do well to try this test upon them. It is not the cord on to the small pin, however, there should be likely they will try it a second time. several turns of the other cord made around the mandrel; the reciprocating motion is then given to the lathe by the treadle, care being taken not to make s complete revolution of the crank. I must apologize for trespassing so long on your space, but trust the interesting character of the subject may plead as an excuse. HYPERION. TOOL HOLDER. [1052] I INCLOSE a drawing of a tool holder intended to supersede the ordinary forged steel tools for self-acting lathes and planing machines. Fig. 1 is a side view of the holder and tool complete. Figs. 2 and 3 respectively a front view and plan of the This leads me to another remark, Why is it that opticians do not adopt more generally the practice of cementing their object-glasses? I know it adds to the difficulty of correcting the spherical aberration, as the 3inner surfaces must be made to coincide, that is, must be marked to the same radius; but the curves once found, optical glass is now made of so uniform a quality, and the refractive index so nearly similar in glass of the same kind, that this can hardly be styled a great difficulty in the way. When one sees the large amount of moonlight reflected from the first surface solar eyepiece, and remembers that a similar, if not larger, amount is thrown back into the outer air, by the two internal reflections in the object-glass, he cannot help wishing such waste might some way be saved and utilized. While speaking about object-glasses, I may be permitted to mention a test which has pressed itself upon me as one of the most rigid and severe that could be applied to discover the quality of any objective over 4in. In all the drawings and coloured prints of Jupiter which have recently been in our hands, there is an absence of one characteristic which must have attracted the attention of the careful observer, who is using a eally good instrument. On examining the equatorial belts of the planet, he must have observed a cloud-like mottled appearance, something like the "faculæ " on the su's face, only more "cumulus:" sometimes it reminds the observer of the white steam as it rolls in volumes from the chimney of a locomotive on a cold day; at others of the piles of snow clouds as they often range themselves along the north-east horizon, and shine in the rays of the setting sun. Not that these are at all necessarily analogous phenomena, but the cloud-like appearance is there and suggests the idea that masses of cumulus vapour are sweeping over the darker body of the planet below, and shine in the light of the distant sun. I have spent hours watching this beautiful phenomenon in my 8 in. "With-Browning" telescope; on clear nights, when the air is fine and steady, it is beautifully apparent. Lately, since I have been compelled by professional duty to reside within a large city, where I cannot so well use my reflector, I have observed the same phenomenon, very well defined, in a most admirable 4in. achromatic by Wray. This leads me to suppose that it is not absolutely necessary to have a large aperture to see these cloud-like appearances; provided there is a sufficiency of light, it is only necessary that the aberration of the object-glass should be perfectly corrected; that must be the case, for it seems to me, that in grasping these delicate shadings on the planet, you are but putting in practice an old test for the correction of objectives-a white-dashed wall lit up with a blaze of sunlight: any telescope which will separate each grain of mortar on such a wall, and show all the gradations of light in the general whiteness, is no mean instrument. Ordinary amateurs, however, would hardly be able rightly to estimate the severity of the test, for except they had one perfect instrument to refer to, their idea of perfection would be vague indeed. When using a solar eyepiece on my 8hin. reflector, I have sometimes seemed to detect similar macula on the disc of the planet Venus. Perhaps some of your readers would direct their special attention to this at the approaching appearance of that planet. One word more about testing. I quite agree with Mr. Purkiss in thinking that double-stars are not the best and highest test for an instrument; planetary definition is the real crux. If double-stars are to be taken at all, as they perhaps must be, then let the question be, With what power can you divide such and such a star? and that telescope which divorces doublestars of a distance near to the separating limit of the aperture, with the lowest power, is the best instrument. The smallness of star-discs is a good test of the fection of an objective, and the smaller the discs the easier is it to divide double-stars with a low power; but after all there is no test like the one mentioned above, planetary definition. per Should the telescope not be of sufficient aperture to attempt the above delicate test, let the amateur who wishes to search out the quality of his instrument to the very utmost turn it upon the same planet, and having discovered that the air is steady and fine (if it be not these there is no use in his trying to obtain accurate results) let him apply the highest power eyepiece he has (100 to the inch if possible) and examine its disc carefully. There will be small light, but complete sharpness of definition, if the objective be of great excellence; no colour to pain the eye, or indistinctness of outline, but well marked and clean definition. With a power of 880 on my 4in. the disc of Jupiter, although needing more light, is as sharp as with 200; and I remember well having examined the same planet on one beautiful evening last year with my 8in. reflector and a power of 500, and shall never forget the FIGL FIG. 3 SUN'S APPARENT [1054] I HAVE read lately, in a work entitled "Cosmogony," that although the apparent diameter of the sun in Europe in December is 82′ 36", yet in Van Diemen's Land it is only 31 30 during that month; and that while in Europe, in June, it is 81' 80", in Van Die same. The holder per se is made of lin. square cast-steel | men's Land it is 82' 36", thus annulling the argu The tool, x, is a flat piece of cast-steel gin. x in., and; is shaded in the drawing. The wedge for fixing the same on the slot in the holder is marked black in the drawing. These three parts constitute the entire apparatus. The two facets, ss', forming the end of the cutter meet at an angle of 90°. The angle i ad is 40° 12'; e a d, 45°; e af, 40° 48'. It follows according to trigonometrical principles that the cutting edges of the tool will be 60°, and the facets, 8 8', will allow 3° clearance; both of which conditions, I believe, are theoretically, as they certainly are practically, correct. The cutting point, a, should on no account be placed above the centre line 33'; for should the tool be overloaded it will then bend from the work, whilst if placed above that line it would dig into the work, and something must "go"-the strap will slip, the centre give way, or the tool break. The above tool holder, if used in connection with some contrivance for horizontal adjustment, will be found to answer admirably. As will be seen from Fig. 8, it will work out a square corner and clear itself, will cut in either direction, and is applicable either to light or heavy work. THOS. WATSON. SCREW CUTTING APPARATUS. [1058] CUTTING a true screw is one of the most difficult things for an amateur to accomplish, and as any tool that will simplify the process will, I am sure, be acceptable to many of your mechanical readers, I send the accompanying engraving and description of a tool that can be fixed to any lathe. I give it in the words of the maker. "By the use of it an experienced hand is enabled to cut screws, the machine giving him a true lead, after which they may be finished by turn ing in the usual way; the only attention requisite being the steady holding of the screw tool on the small rest and giving the necessary reciprocating motion to the lathe. In use, the machine is clamped to the lathebed in the same way as the ordinary hand-rest, and as parallel to it as the eye is capable of judging; the projecting lever is extended to the opposite side of the lathe board, along which is stretched a cord, which, being looped on to the small pin at the end of the | ment that the earth is in perihelion in winter, as deduced from the sun's apparently larger diameter. But are the above statements facts? I should be very glad to hear from some one who has had a practical opportunity of noting the sun's diameter in the southern hemisphere (of whom there must be many among the readers of the ENGLISH MECHANIC) whether they are so or not. So long as a statement like the above is allowed to be circulated without controversy, the elliptic theory of Kepler stands in a questionable position, and in the interest of science and truth an assertion like the foregoing should be sifted to the bottom. GEORGE BELL. PNEUMATIC QUESTION. [1055] MR. RHODES' question (p. 250, let. 873) is so simple, and one upon which experimenters agree, that I doubt whether he will receive a reply from any of our "princes" of science, as he calls them; and if he does they will probably tell him there have been sufficient experiments made and recorded to preclude them re-opening the question; therefore I offer the following additional remarks. What he cannot understand is, that air sealed in a bottle and placed within another vessel from which the air shall be exhausted, can possess an elastic force equal to 15lb. per square inch. To show the elastic and expansive properties of air, let him take a silk bag, which, when filled with gas, would form a sphere 6in. in diameter, half fill it with air and tie up securely, and place it within a strong glass vessel 12in. in diameter, from which exhaust the air. As soon as he commences to exhaust the air from the vessel he will perceive the half-inflated bag increase in size until the air is nearly exhausted, when the bag will be inflated to its fullest extent, and will burst auless the silk be sufficiently strong to resist the increas ing expansion of the air within. Admit air into the vessel again, and the air in the bag will decrease to its original volume. Again, a pint of air taken to the light of three and a half miles will expand to twice that volume, and if corked up will press with a force of 7 lb. against the interior of the bottle, because the atmosphere at that height has only a pressure of 74lb. per square inch, and at the confines of the atmosphere the bottle would have to resist a force of 15lb. to the square inch, which is due to the expansive qualities of the air corked up. If he will procure a piece of tube, 24in. long and lin. diameter, with a stop-cock at one end and an airtight plug at the other, he will find that if he will open the cock to permit the plug to descend into the tabe 12in., then close the cock, it will require a force of 7 lb. to pull the plug to the top. Or, on the other hand, when the tube is full of air, put the plug in at the top (which will be analogous to the cork in the bottle), and |