DEO, 1881. pitch is in the direction of the motion, and then conratively little cut or polishing goes on, while we the motion is crossed and reversed continuy, the grain of the pitch is kept perpendicularpen comparatively much cut or polishing goen. Here, then, I say, is plainly revealed to us thict that the polisher is divided into a numberof ze of unequal degrees of cut or polishingone zonolishing much more or much less than the 18 even as next, aro on from the centre to the circumference of the pher, which unequal polishing would impress it on the face of the speculum, and produce thzones that Mr. Lassell invented the sliding tion of the speculum on its face-plate backwa and forwards to cure, but this only did it by mng one error obliterate another, and not by remag the cause of the error, which is the object weght to aim at. I may just explain, for the benefit any who have a Lassell machine, or wish to work that principle, that this curious zonal effect isoduced not by the proper motion of the polishen its loops round the centre of the speculucombined with the proper motion of the speculuround its axis, for with these combined motions one the lines would be the same all over the surf, but by the motion of the polisher on its axis-e., round the pin that moves it in its loops (ich motion is caused by the friction betweeme polisher and speculum) combined with throper motion of the polisher in its loops round t centre of the speculum. And that, to improve the therefor the proper way Delarue Lassell nachine not did, b so controlling the revolutions of the poler around the pin that moves it, as to keep it to that which the polisher takes up on an averagehen left uncontrolled," (which seems to be abounce for every five loops), but by so controlling revolutions on its axis that it shall rovolve v slowly, I should say once for every 50 or 100 lps-i.e., so that this motion shall not apprecity alter the shape of the loops; then the directioof the motion between the speculum and the polier would be crossed and reversed the same fall zones, and thus do away with the zonal qualities of polishing by this form of machine when the polisher is left uncontrolled. I did n try this improvement, as I saw the defect d not exist in the Rosse machine, and I abandod at least for a time the Lassell machine; but I da say after I have exhausted all that can be done y the Rosse machine I shall return to the Lasil's, and try to perfect that form of machine or its continuous motion has so much to commd it to our admiration. Perhaps all this has ppened for the best, for the majority of amateur hat have machines have Rosse's form, and I a now describe to them what can be done by his form, and very good specula can be produced by it; thus those who have this a drawing machine ed not despair, I hope to give of my fon of machine on this principle further on. I feel must again refer to the subject of beginning tfigure when we begin to polish, or what we may ore correctly describe as beginning to bring themachine and conditions into that mutual arrangennt that they will work a parabola; then all we shl have to do will be to maintain these condition &c., till we have polished out all the emery miks, when the speculum will be finished without ay further trouble, and in the time only that it taes to polish-we shall thus save a lot of time and rouble. It is not generally known by amateursthat during the polishing, which will take abot eight hours, there may alternately be given to he speculum by machine working, a sphericalud parabolical figure some dozen times or more. This will not appear strange, when we remembethat the difference, even on the edge of a 4ft. spculum with a 48ft. focus, between a sphericalud parabolic figure is only the 21,000th of an inc, and that the depth of the emery marks cannot biless than the 2,000th of an inch-Ishould I intend to think nerer the 1,000th of an inch. measure his exactly the next time I do some find grinding. Now, it is evident that in this 1,000th of an inh there is ample room for a dozen 21,000th of an inch. Now, as we in reality partly put a figre on the tops of the emery marks such as the mrhine and conditions will produce, even in the fist half-hour we polish, and can, by testing by Foucault's test, see what figure it is, we can then begin to alter the machine and conditions, if we understand their laws, so as to bring the figure nearer to the desired parabola, now this is figuring, and so on for every future half-hour's polishing, and thus we utilise our polishing time for figuring as well. I generally, after the third or fourth half-hour's polishing, get or arrange the machine and conditions to produce the parabola, I have then only to maintain these and go on to the end of the polishing. I hope to show the amateur how to do all this for himself; but let him remember he must pay particular attention to every law I shall have to bring before him, and explain to him; and when he has mastered the application of these laws, all will become as simple as the chemistry of this day compared with the alchemy or chemistry of three or four hundred years ago. I think our next letter will be on the use of the side motion in the Rosse machine. We will seek to H. A. Wassell. decide whether it be of use or not, and what is its action. Addenbrook Villa, Love-lane, Stourbridge. THE ADJUSTMENT OF REFLECTORS. Mimas. SILVERING MIRRORS, &c. [19492.]-AMATEURS may thank Mr. Brashear for a good and simple method of silvering. I have tried it and can strongly recommend it; it reacts better with double the quantity of quires careful management in large and strong baths; candy is, of course, richer in sugar solution-especially if white loaf sugar is used; sugar saccharine. In reply to Mr. Wassell, the 37in. speculum was I note Mr. Brashear's remarks on my method My plans are a little varied according to circumstances: the methods given in my hints are reliable and best for the amateur. He is not so likely to succeed by blocking, and, I may add, that by this method I made the Gin. plane for the 37in. speculum. I cannot advise the making of planes singly. By accident small portions of plate-glass are flat, but it is a rather tiresome search to select them. While writing about planes I may, perhaps, remark that though a new form and outlandish position has been made out for the plane of a Newtonian, I have no doubt telescopists will allow it to retain its original and proper position and form-viz., an elliptical form, and placed in the centre or axis of the tube the same as the mirror. I quite agree in the opinion of the author of the new idea that "up to to-day (!) inno instrument by the makers will this position, &c., of the plane be provided," but I don't share his apG. Calver. parent opinion that to-morrow the "makers" will certainly adopt the new idea. season. our THE LANTERN. [19493.]-WITH the advent of dark winter nights the pages of the "E.M." have been generally enlivened by some correspondence on this subject, and chancing to look into the Vols. for Dec., 1875, and Jan. 1876, I noticed what a fund of information there was, either treating on the lantern itself, the best light, oxygen gas, &c. Hitherto very little has been evoked on the subject this With the idea, therefore, of stirring up lantern friends I pen these lines, and with pleasure I note that our valued contributor, Mr. Lancaster, has something new in the way of a slide-holder. Without saying anything that should be, in view of that gentleman's very reasonable remarks in connection with it, like a revelation respecting it, I would say that some four or five years since I tried what must have been a somewhat similar idea, but possibly not so completely worked out. The basis of the arrangement, of course, fitted the slide-holder, as no doubt his does; but the difficulty I found was that one had with a biunial to reach over the fronts so to remove the used slide, when the holder was on the farther side to the operator, and notably so when the 327 There are also two other matters that I should will see what I mean without stating matters bottom lantern was changed. Mr. Lancaster further; and will he say if this is remedied in his new plan? If so, it certainly is a great improveoperator, being sometimes productive of broken ment; the panoramic system, with a careless slides, owing to their being pushed out, the operator having forgotten to remove the used slide. like an opinion on, either from Mr. L. or anyone else who has had experience. It is, What is likely Mr. Wright mentions Mr. Hughes' new 4-wick to be the best oil-light for the season? I see that lamp; but he does not mention the price. I am at all times open to obtain any real improvement, so that I should like some additional information on the matter. By the bye, Mr. Lancaster has, I fancy, a new oil-light. I should be glad if he would tell us something about it. The other item I was going to name is if anyone has tried the etho-oxygen light? and if so, I should like to comThe lantern always has been a very great municate with them on the subject. Some favourite with me, and I therefore welcome the dark season as giving full scope to its use. may say that it has lost its popularity. Quite so, if in the hands of incompetent persons; but the large audiences I had the pleasure of meeting last winter tend to prove that its fame is not yet quite lost. A good illustrated lecture will, in the hands of most competent men, coramand a fair if not a large audience-and I find that the display of dioramic effects and statuary properly shown at the close, never fail to elicit warm applause. As an educational instrument it is certainly unsurpassed. The chief thing in which I fancy we have come to the end of improvements is the production of the proved; and with the new jet I mentioned some oxygen. The light, I think, will be even yet imtime since the hydrogen being taken from the main-both economy of the oxygen and an improved light are both gained. I trust some brother lanternist will have something to say on the subject Sunlight. shortly. flat. screw passes. LANTERN SLIDE-HOLDER. [19494.]-As the season for exhibitions is now new lantern slide-holder may be of interest to some approaching, the accompanying illustration of a of "our" readers. I have used for some time a stepped slide-holder, but with dissolving views I find it a great tax to remember the size of slides, fore, devised this holder, which is automatic, for three back, throughout the exhibition. I, thereany two sizes. Mine are made to the square and the Woodbury size, as what transparencies I make Ferrier's I had I took to pieces and made up to of course I use -plates for, and what slides of here come in handy, as they come perfectly clean Woodbury size. The 1-plates you have failed with with hot water; so having reduced our stock of unframed slides to two sizes, we proceed to construct the frame, which takes a quarter of an hour. we must have it perfectly Take a cigar-box lid, soak off the paper, and dry Cut the lid before the fire, turning it about as any warping to 8in. by 4in; clean smooth one side thoroughly is observed, as the edges and with sandpaper: on this side we work. Referring The shaded rectangle to Fig. 2, we have the lantern-front with front plates separated by a pillar at each corner, through which a below is a brass bar fixed to the two bottom pillars, on which bar rest the slides, each one being registered by a "pin" driven into it (and afterwards adbar. The slideholder of course has this pin, shown justed) which is stopped by the end of the brass also at A (Fig. 1). The square and Woodbury slides are shown in position by the dotted lines the left-hand of the slide-holder. The operator over the hole cut in our cigar-box lid 3in. from stands on the right side of the lanterns. Two bars of wood are fixed to the top and bottom Their shape is seen in Fig. of the holder. the slides 2. The purpose of the upper one is to hold which prevent pins" one supports a several falling forward. The bottom strip of brass 1-16in. thick, in. wide, and about 11in. long. One end, as B, may be turned up to form a convenient handle; the other is also turned up in. to catch against pin C, to prevent its being pulled out too far. The bottom bar A is sloped a little towards the body of the holder in order to give the slide a bias in that direction rather than tance from condensers and objective. On the brass the other, so that each slide may be at equal disstrip, at about 3in. from each end, there is soldered a little block of brass 3-16mm. cube. If, now, we draw out the strip by the handle B until we are touches block D, push stopped by peg C catching the other end, and, it will be seen having placed a "Woodbury" slide on it so that is stopped at the proper the right-hand corner it back as far as that the slide we can; And very properly. "Sunlight" will find that in the advertisement pages, to which such information should be confined.—ED. be in form of a number of detached segments of circles, the working parts of fittings to be cast central on one of the segments; the edges of these plates might have impression left to denote centres. Three segments of circles lin. radius, with centres jin. apart, might be taken as a standard for plates; this would give a length of 24in. To hang a sash on these pivots, draw a horizontal line, as is usual, on the stile of sash and frame, return it on edge, a central line at right angles to this. Where the lines intersect, place the middle segment of plate; mark the centres on this line. Of course the intersections of the lines =will be one centre; three hallow holes on the edge of sash, and the same on the frame, made with an inch boring-bit, would insure a much more rapid and satisfactory job than it is possible to accomAplish with oblong plates that have to be sunk into wood by means of chisel. There is no need of details for thumbscrews; this principle, with a slight modification, might with advantage be applied to sash-pulleys. In sketches, diameter, and screw on as shown. They must be before any definite figures and measurements be perfectly true with each other and square with the given, one must know the size and resistance of sides, so that when the fan is inserted it shall run lamp, also the power of light required. To charge true with the sides. Now shoulder down the spindle a Faure's battery from a Bunsen's is very much in lathe to the holes in bearings, to allow of free-like pumping water up a height to use it again dom without end shake. Now fit on the small through a turbine. grooved pulley I, and it is in condition to be tried. As regards the question of dynamo machines, A A H Fig. 1 is a shutter stud; Fig. 2, thumbscrew; Fig. 3, sash-centre; Figs. 4 and 5, sash-pulleys. R. Gough. 123, Lower Kennington-lane, London, S.E. HOW TO MAKE A FAN. [19500.]-To make a really useful fan is not a difficult task, providing we have a correct knowledge of what we require before starting. Let us suppose, then, it is a small domestic fan that is required; the fan proper, or the part that revolves, is first to be decided upon, unless a set of castings can be obtained, in which case it matters little what part we commence with. But these instructions are intended for those who cannot obtain castings, and are perforce obliged to make shift as best they can. Fig. 1, A represents the fan in section; B is the outer case; Fig. 2 is a section taken through the line of centres of C, and A (the letters refer to the same parts in each figure). A careful inspection of Fig. 2 should be made, as it is here the working parts can be seen. First, we have a small spindle turned out of a piece of in. round iron or steel, straight and true; on this we fasten three discs: the centre one, J, is plain and blank; the outer ones, F, are open in the centre, with a bar across, as shown at F 1; these discs are 24in, diameter, with lin. holes in them; the bar is bored to fit the spindle, aud fixed 2 in. from outside to outside, the blank one being in the centre. Now turn these true in lathe, top and sides; now make two discs of tin plate 5in. diameter, A, Fig. 1, which are dished as A, Fig. 2, with holes in centre to match F 1; rivet or solder these to the inner face of the outer discs, and swing in lathe, bending them carefully until they run true. Now for the blades: these are made of tin plate, cut to the shape seen in Fig. 2, A, and curved as seen in Fig. 1. These blades are enough for a fan this size; rivet or solder these blades in between the discs, inserting the centre of blade in saw-gates cut in centre disc for that purpose; see that all are true and perfectly balanced in lathe, adding solder to the light side until perfectly poised. Now for the case: the sides of case may be made of sheet-iron or wood-let us say mahogany in. thick cut to the shape seen in Fig. 1, B. If the curve G be adopted it will look better in some people's estimation, or the sharp angle K may be adopted. If the former, a piece of tin must be bent to the angle K and fixed inside before closing up the case. The object of this is to prevent the air being carried round again with the fan, instead of being delivered into the discharge-pipe H, as shown by the arrow. Having put distance-pieces between the sides to keep them apart, cover the space between them with stout tin plate, leaving one side loose to be removed for the insertion of the fan. The distance must be such as to allow of the fan running freely without touching at F F. Fig, 2, DD, show the bearings in position. D1 is an enlarged view of same, which must be as narrow as is consistent with strength, in order to allow a free passage for the air entering, as shown by the arrows. Bore these out fin. The pipe H, also of tin plate, is oval at the end next the fan, and narrowed off to in. at the delivery end, which is round. The wheel C is shown in position, and is grooved round the edge to carry the band for driving the fan by the small pulley I. This wheel turns on the stud in bracket E, shown apart from the wheel for the sake of clearness. One spoke of wheel carries a boss, in which is inserted the handle. The arrows show the direction of motion. The whole may be fixed to a board. or on a pair of light iron standards, the height of which will be the height of the firegrate. I know there are more simple forms of fan than this. For instance, the blades may be screwed on three arms of a boss fixed on the spindle, thus avoiding the discs; but such a fan will be noisy. The one here described is efficient, and whether 4in. or 4ft. diameter, will, if well fitted, be silent. And allow me to say a word to amateurs: Never begrudge a little trouble, if thereby you secure a better result. I have seen fans, both by amateurs and practical mechanics, which were simply intolerable, and had to be replaced by bellows. Lockstitch. PURE ZINC-ELECTRIC LIGHTDYNAMO-MACHINES. . [19501.]-I SEE the question of "pure zinc " raised in "ours," and thinking that I might do some good by stating some experiments have made, I venture to do so. In the first place I tried years ago, when working in the Owens College laboratory, to prepare pure zinc by distillation, but without success; and afterwards, when requiring pure zinc in the laboratory of a chemical works where pure chemicals were made, I again tried by reducing carefully prepared pure zinc compounds, but could not get pure" zinc, as in this case it was sure to be contaminated with silica, &c. As to "P.'s "suggestion of preparing pure zinc by electrolysis it is certainly the best method if he could only do it. My results at electrolysis of not only zinc but other metallic solutions have not been crowned with success, as I have not yet met with the substance for the anode. For instance. suppose one is working with the chloride or sulphate of zinc, the zinc goes to the cathode, and the SO, and Cl to the anode, but my experience is that unless you get something that will combine with the SO, and Cl at the anode, you get no metal deposited at the cathode. Further, the compound formed at the anode must be insoluble in the solution in which it is obtained. Text-books on electrolysis forget to tell you these little things. "Zu," in query 45463, requires information about the electric light. Let me tell him that the game is not worth the powder. Why not-supposing a hand-dynamo powerful enough-use the electricity direct, as otherwise you would have to charge a series of Faure's batteries for perhaps 48 hours to obtain anything like a light? The same as regards the Bunsen battery. You had far better use direct, or else you might have 10 Bunsens charging a Faure's battery for 24 hours; but allow me to thank Mr. Lancaster, Mr. Hanson, and also "Anglo-Dane." To Mr. L. allow me to say that I prefer the experience of the many valued correspondents of ours" to any results which may appear in connection with the forthcoming Crystal Palace exhibition. Also, makers want to make hay while the sun shines, and so they seem to me to form a sort of league to keep the prices up, give no comparative results, and to keep those outside in the dark as to the best form of construction. To Mr. Hanson my best thanks, but who is like many more in giving a description of dynamos-although he gives length of wire on armature, nothing is said about length of wire of field magnets. He states the R. of armature to equal the R. of field magnets. If what Dr. Siemens has stated-viz., the R. of armature to be 1-10 R. of field-magnets, or Mr. Kennedy that the R. of field-magnets should be 5 times the R. of armature, it seems to me strange that the Siemens machine referred to should be equal in R. for both the armature and field-magnets. This is a point that wants settling, and I think that some of our readers could give us the benefit of their experience. Also, I am sure that if somebody could give us some data to work on it would be of great service to many readers. For instance, take two examples: required, a dynamo to give, say, 2,000-candle power, and one to give 5,000; what size and form should machine be with length and thickness of wire on the armature and fieldmagnets with the R.'s in both cases, and how to calculate the power required to drive. Seeing how rapidly electricity is coming to the fore, it is really time something was known definitely about the right construction of dynamos, and if there is a journal more suited than any other to settle this important question, it is ours; therefore, I appeal to all to contribute their mite, so that those wishing may, during the coming winter, get their drawings and patterns ready for their dynamo machines. As to our friend, "AngloDane," I shall be glad to hear of the success of his machine; saying what it will do and also the length and R.'s of wire on it with power required to drive. I quite agree with him as to the space taken up with matters relating to tricycles, although a great lover of the sport, having been a bicyclist some fourteen years. Cannot our best of friends, "Sigma," give us a wrinkle about dynamos? Quæstor. DYNAMO-MACHINES. [19502.]-I AND many others, doubtless, have been waiting patiently for particulars of construction of dynamo-machines, and can testify to the boon it would confer to have the subject discussed with something akin to the skill and acumen that bicycles and tricycles are enjoying at present. I live in the country, and the exhibition to come off in London will do little for me in the way of giving me an opportunity of seeing what is going on myself. I have been looking for a practical answer to questions like those of "Quæstor" for a long time, but the answers are always to-morrow and yesterday, but never to-day. Will some one not tell us how to construct, say, a dynamo on the Gramme system, to give a current which, worked in conjunction with one of Faure's accumulators, would be capable of lighting, say, twenty to thirty Swan lamps? It is not necessary to assume that the mechanical skill, electrical knowledge, and perseverance are not forthcoming. In the age of electrical discoveries are amateurs never to get beyond electric bells and telephones? I am confident our editor will not object to propose particulars where so many are interested, when we often see whole pages given to matters of a purely personal interest. All we require is particulars of size of armature and magnets, length and number of wire required, plan of commutator, speed of revolution, and a few other wrinkles to set us going. Has Mr. Kennedy nothing to say or suggest? or is it possible that the thing cannot be done and is this the cause of the melancholy replies of Mr. W. J. Lancaster? Hybernian Celt. The points and signals at Tayport are said to be interlocked, but the line is not worked upon the block-system, and the true cause of the disaster is due to the fact that the directors and officials have neglected to provide those well-known appliances for ensuring an interval of space between all trains. During the time the shunting of the coal-train was being performed the passenger-train from Burntisland approached, and was slackened at the "distant signal," the driver whistled, and Thomas Dippie, the signalman, thinking for the moment that the coal-train was clear of the main-line, lowered his "home-signal." The driver of the passenger-train received no warning of any kind until he felt his engine dash into the rear of a tender. Had this tender carried a tail-lamp the collision would have been entirely avoided, as the passengertrain, being fitted with the Westinghouse brake, could have been pulled-up in the shortest distance. The collision was very violent, and five persons have unfortunately lost their lives, and others are very seriously injured. On Saturday Mr. Morrison, Procurator-Fiscal, made an investigation at Tayport; from the notes of the proceedings now before me, it is quite clear that the Court was perfectly ignorant of the subject, as is shown by the utter absurdity of some of the questions asked. However, the result was that the Procurator-Fiscal gave his order that the signalman Dippie should be arrested and conveyed to Cupar prison, which order was at once carried out. One or two facts still require further explanation before I can form an exact opinion as to the amount of negligence of which this man has been guilty. I do, however, most strongly protest against the signalman being arrested and taken to gaol like a common felon, more especially as bail to any amount was forthcoming, and there was not a shadow of an idea that this man would try to run away from justice. I may mention that Dippie is about sixty years of age, and has been in the service of the company for about thirty years, throughout the whole of which time he has borne an excellent character. It appeared to me to be most unjust to send this man to prison, and therefore I telegraphed and wrote my opinion that bail should be accepted; in reply, however, I was informed that the guard of the goods train had just becn also arrested, and conveyed to Cupar. Sheriffs and procurators- fiscal in Scotland, are vested with considerable powers, but unfortunately they are in nearly all cases very severe indeed upon railway servants. The Rutherglen accident, and the imprisonment of driver McCulloch is one of the cases in point (see ENGLISH MECHANIC, Vol. XXXI., page 305). bers of Parliament, and, if necessary, application will be at once made to the Lord-Advocate. Clement E. Stretton. Saxe-Coburg-street, Leicester, Dec. 2. P.S.-It gives me very much pleasure to state that I have received the following telegram from Tayport:-"The two men arrested in connection with the Tayport collision have been released on bail; much sympathy is expressed for their unfortunate position." TRICYCLES. [19506.]-JUST a word or two on this question, which, strangely enough, is by far more fully, and let me add, carefully discussed, than in any journal devoted exclusively to the sport. What I have to say is the results, so far as I have been able to clearly demonstrate, by repeated and careful experiments; and so far, they show in the clearest way possible that a large wheel is, when it goes beyond a given size, a drawback, whether geared up or down for everyday riding. And the great points to which I would wish to draw attention [19505.]-THIS problem (letter 19371) may be are, that if we want a machine easy to propel, and a good hill-climber, without the use of special apsolved approximately, by calculation, as follows:-pliances, such as are now attached to several In figure, page 209, join B C, B D, and C D. Let B C C. E. S. INDIAN RAILWAY PROBLEM. chains. = m Then angle B C D 1719 in minutes, And chord BC And chord BD By trigonometry = R 2 R sin. BDC 2 R sin. 1719 m + К BA Sin. B CA = sin. BAC. =m, CD = ", and R = radius, all in makes, the largest practicable size is 40in. or thereabouts. The greater the strength of the rider, so may the wheel be an inch or so larger; but 40in. is very close to the limit. That the makers are themselves finding this out is proved by the general introduction of that size wheel. Therefore, if Mr. Macdougald means large steering wheels compare. tively, I quite agree with him. If he advised large drivers, then I must dissent. The next leading) point I am quite convinced of is that length of backbone is an advantage. Not only does it make the machine run steadily, but it prolongs the line of traction, and "C. E.," I note, has found this out; and I am glad, amidst the volume of theory that "C. E." has spoken up in the practical way BC BA Sin. BDA = sin. BAD. BD But CAD + BDA ВСА + CBD .. CAD + BDA БСА R' = -- = = CBD theory which I have refrained from mentioning as being theoretical only, but which is, nevertheless, quite correct. I would wish to say to "Paugul" that I cordially accept the mauly and straightforward statement he made at page 258, and I am quite sure he will accept this in the friendly spirit I make it in. Let R' the radius which gives this angle upon CD, he has. And his last paragraph supplies the needed 1.7192 then C B D = 1,719, and R' = CBDш minutes and ought to be R. Assume a radius and calculate as above, and if R' does not agree with R, then try R' in place of R, and calculate again till R and R' nearly coincide. N.B.-The constant 1,719 is the angle in minutes at the circumference standing on an arc = radius, 180 × 60' and is = 1718 87338' more exactly. EXAMPLE. As instancing the difference of opinion, see Mr. King's letter. He advocates a forward thrust, in preference to the vertical one. Well, I thoroughly believe this to be a matter of use. I am personally accustomed to the vertical thrust; and chancing to have to ride one requiring a forward thrust, the propulsion of the machine about a mile so exhausted me that I had doubts of reaching home; yet I afterwards rode the same machine, with the seat altered to allow of the vertical tread more, with the greatest ease and comfort. If we come, not to technicalities, but to strictly plain terms, surely "No. 170" (page 305) will not gainsay me on the question of double drivers. What is a double driver? Why it should be that, in ordinary running, both wheels drive equally. But on meeting a resistance, the wheel meeting it should drive-not the one which meets no resistance. This is my theory and definition of a double driver. The "Salvo" does not do this; therefore, I do not consider it a double driver; neither does it comply with the required test that, in turning a corner, the outer wheel should drive. Here the "Salvo" again fails; therefore, I again condemn the so-called double-driver again. But in this is the difference, that the "National Special" meets that difficulty whilst the "Salvo" does not. With the former, the outer wheel drives on turning a corner, and the wheel meeting the most resistance is the one doing the most work. In paragraph 6 he gives a correct solution of the front-wheel question; but the lengthened backbone to the rear-steered machine does much to meet that difficulty. Paragraph 8I see he is quite right also, except on the question of the brake. Unless the machine be running very fast and the spoon-brake is applied suddenly very 11.566193 = 1.694221 BDA = 48° 8' = 9.871972 38° 28′+48 S'- 73° 12′ = 13° 24' hard, it will not tend to lift the trailing-wheel; and [19507.]"FABER" (19425) and "Paugul" (19452) have suggested improvements in the seat I described a little time ago. To the former I beg to say that I have never noticed any defect in the working of the simple joint at r as figured, but there is no reason why either a ball-and-socket, or some kind of universal joint should not be rsed with advantage. If "Paugul" will communicate with me, it will give me pleasure to send him sketches for his criticism of how I propose to meet the difficulty he apprehends. The seat arrangement, as figured and described by me, was only intended to illustrate a new principle in construction, and not as an unalterable design equally applicable to every build of tricycle On my own machine, where both cranks and connecting-rods are adjustable, there is no need tha 38° 28' +49° 5′-73° 51′ 13° 42′ = 822 and the seat should be so. However, in consequence o 1719 × 30 822 = 621, and nearly = R, &c. Under the circumstances therefore, I have now requested that both men may be admitted to bail, The problem is sometimes indeterminate, as there and have, at the same time. At the facts of is nothing to show whether the angles BCA and the case under the notice Botch Mem-BDA are acute or obtuse. C. E. numerous inquiries how to adapt it to machine with unadjustable cranks, I have recently given a good deal of attention to this matter, and believe) have thoroughly mastered it. It would take to much space to describe how, and illustrations woul be requisite. Besides, different builds of machin would need special adaptations. I shall at all pressure per sq. in. (either will do), I shall have [45172.]-Asphalte Roof.-There seems nothing objectionable in the materials used; but why not use slates? Anyhow, the rain-water would require filtering, and if a cheap and light roof is required, that can be made by tarring the roof first, then laying on sheets of strong paper and tarring pitch and tar, and thinned with coal-tar naphtha. again. The "tar" to be made of equal parts of -ESSAR. [44999.]-Self-Feeding Fountain.-Your best way is to allow the water to flow over the wheel the water back into the tank again, and to provide as you first proposed, and attach a pump to force the necessary additional power, connecta magnetoelectric engine with the water-wheel. But there is no motor of that class to be had that can be ing the drawings of a new compound engine (not [45206.]-To "Sunlight."-I am about startworked by permanent magnets. It must be a tandem); if it will not be asking too much of you done by electro-magnets. I notice that Mr. King's views (19478) upon leg- that have been suggested in this journal can easily in the new one the bore of high pressure to be 3 in. The various plans to tell me the point of cut-off of steam, assuming thrust and back-purchase coincide with my own, be found by referring back. A battery will in that by 5in. stroke, and the low Sin. and stroke, of as he will find by referring to back numbers. To "No. 170" (19180) let me express my thanks. Fuller, or other constant form. If the water be case be required; but that might be such as the course, 5in. also; shall I still have to retain the I am thoroughly familiar with the driving principle allowed to flow on to the wheel, then the descend-3), that is, cut-off 6-10th of stroke? Of course, same size eccentric as in my present engine (33 by of the "Salvo," but not being myself a rider of this machine, I did not feel called upon to defending water would put into the wheel a given quantity that should be cut off sooner in the bin. stroke. In of power to help to counterbalance the column of your reply to my query of Nov. 11th, you state I water to be lifted by the pump, whilst the electro- should not require so much steam in the highmagnetic engine would supply the deficiency.-pressure cylinder, and in both cylinders is it requisite to cut off the same part of stroke.-AMATEUR. it, so I considered putting a question would be the best way to elicit such a valuable description as "No. 170 has given us. W. H. Stacpoole Westropp. Lisdoonvarna, Ennis, Dec. 3rd. REPLIES TO QUERIES. In their answers, Correspondents are respectfully requested to mention, in each instance, the title and number of the query asked. [43942.]-Hydrodynamic Railroad Brakes. -I must express my obligations to "Essar" for his reply to my inquiry re "Hydraulic Railway Brakes, in "E. M.," July 22. I have little doubt "Essar" is correct as to relative efficiency of merit, though scarcely previously crediting it. I did not know such device had ever been tried or put in practice, except something of the sort in gunnery. Nor do I possess the back volumes referred to. The gist, however, of my proposition consisted in placing a thick cast-iron bored cylinder on the footplate or frame of the locomotive, behind, say, the driving-wheel, this cylinder to contain a The back end of the cylinder to be closed, from it fitted piston or plunger to act on the brake-block. to lead a lin. pipe of requisite solidity up to the driver's position, having also at its top end a lin. cylinder with piston or plunger therein. If, now, the pipe and the cavity in brake-cylinder behind piston be filled with water, the brake piston being 100in. in area, 1lb. pressure on the pipe piston will, by virtue of the "hydrostatic paradox," put 100lb. pressure on brake-piston, fixing a lever over the lin. piston, like the principle of safety-valve lever, the long end being ten times the short llb. at the lever's extremity, will put 101b. on the lin. piston and 1,000lb. on the cylinder-piston. The point of the lever now screwed down with a force of 201b. will put 2001b. on the pipe piston and 20,000lb. on the brake-piston, or a binding force of over 9 tons against the wheel-enough, possibly, for the most common emergencies. What the power exercised by the Westinghouse and other brakes expressed in tons is I do not know; 50 or 100 tons might, with facility, be applied with water. The continuity I proposed to effect by side rods from block to block along the train, so putting the binding force on every wheel at once.-HYDRO DYNAMIC. [44637.]-Puckle's Conic Sections (U.Q.)-I feel sure that no such key has been published. OLDHALLIAN. SUNLIGHT. [45044.]-Oxy-Hydrogen Microscope. I have to correct an error that somehow or other got into my reply of Nov. 18th. I intended saying a Triceratium, 2ft. in diameter on a 6ft. screen.' This I have done over and over again, and I shall have much pleasure in a short time to give particulars of my micro-fronts. I may here give "Antares" a wrinkle, one that may be useful to him. One of the times when I was experimenting upon several new forms of front, I hit upon, really by accident and not by design, a plan for increasing the size of an object at will. I took a double concave and held it in the path of the rays after they had crossed, thus producing a very much greater divergence in the cone of rays going to screen. The position of the concave was alterable, so that the image could either be reduced or enlarged at will. Now, as to micro-objectives: for projection they cost as much to manufacture as an objective for the table microscope, and who will pay £3 3s. to £8 88. for a combination of the kind I described? I would most willingly make them and advertise them, but I know it would not pay me to do so. My objectives have the largest lens nearest to the object, the smaller lenses being convergent cone of rays. If "Antares" will only where they should be-nearer to the apex of the look at the pencil as it emerges from the posterior lens in his power, he will find three-quarters of it useless. I reverse this. I use up all the rays and waste none. "Antares cuts the ground from under his feet. November 11th, he distinctly says that he has a specially good in., by Dallmeyer, specially made for projection. What does this do if it does not in. dorse all that I have said? Why, I would give "Antares" a combination that should be as good as Dallmeyer's in. for as many half-crowns as he paid Dallmeyer pounds. I was not referring to low powers at all when I wrote my first letter. Any combination, with both lenses about same diameter, will do for projection; but show me a 1-5in., 1-6in., in., or 1-10in., that will touch a properly made objective for projection; and although I have had thousands of objectives through my hands, yet I shall then see something I have never seen before; and I shall store in the nerve-cells of my cerebrum something that has never yet been stored there, and when once there it will never be lost.-W. J. LANCASTER. [45124.]-Model Yacht.-If "Landlubber" will procure No. 816, and look on p. 334, he will see tables from which he can calculate the sizes of masts and spars for any given dimensions of yacht. -T. P. ing them to soak for a day, you will probably find [44752.J-Chloride of Zinc Battery (U. Q.)— [45125.]-Incrustation of Cast-Iron Pipes. The battery I am going to recommend to this-Fill them up with petroleum, and after allow querist is a most reliable one. I have made one myself, and it has never failed me yet. Take an earthenware vessel (a white jam-pot will do) to bold 1 quart, or a stoneware jar to stand about 5in. high, and pour into it 1 pint of water; into this put 24oz. bichromate of potash. Let it all dis: solve, and then add 2oz. hydrochloric acid (unkilled spirit). 1 carbon-plate goes into this outer cell, about 5in. long by 2in. wide: get a porous cell of the white kind 6in. long and 24in. diameter. It is necessary that this cell be a wide one. Put into it 1 fluid ounce of chloride of zine and fill up with water. Into this cell goes an amalgamated zinc rod. When the circuit of this battery is broken there is no action upon the zinc. It will last for three months without recharging. It is not so strong as a Daniell cell of the same size. The in [45127.] Fishing-Rod. "Angler" should refer to pp. 218, 287, of the last volume, Nos. 841, 844, where he will find some useful information: but a 16ft. rod is rather a long 'un for a novice to try his hand at making.-J. T. M. [45130.]-Horse Clippers. "Cutler" does not say what shape or make of clippers he wishes to sharpen; but I think he may try what he can do with a file.-ESSAR. "H. W." a brief description of the method [45227.]-To "Chemistiana."-I here give lime, say, to make 60 or 80 gallons at a time, as adopted by some manufacturers of bisulphite of required by "H. W."; fit up a cast-iron vessel, holding about 100 gallons, with lid, and manhole in lid. In the lid are screwed two pipes, one for the addition of sulphuric acid, the other conveys the sulphurous gas away when generated. The castiron vessel, which is heated by means of a furnace underneath, is filled with charcoal, or some kinds of coke answer better; a gallon of rectified vitriol is added, and fire applied to the furnace. When the heat has got up, the sulphurous gas begins to from top of still first to a vessel, made in the shape come off, and is conveyed by means of lead pipe of a Wolf's bottle, containing a little water to wash the gas. The washed gas is then conveyed to a vessel containing from 60 to 100 gallons of water and about 50lb. of whiting or chalk, that is carbonate of lime. This vessel is fitted up with an agitator, in order that the whiting may be kept in contact with the this mixture until all the whiting disappears. gas, which is passing into the mixture of water and whiting. The sulphurous gas is passed into The agitation may then be stopped, and the gas allowed to pass in the clear liquid until the required strength is obtained. When the gas ceases to come over from the cast-iron vessel, more vitriol is added. One charge of charcoal will serve several times, the acid only being added as the gas is required. When, by the addition of acid and increase of heat, no more gas is obtained, the charcoal is spent or exhausted, the mauhole or lid is taken off and the residue scooped out, and sold to manure makers.-CHEMISTIANA. [45232.]-Speed of Boat Engine.-If "Nemo" will be advised, such a boat as he proposes is totally inadequate for use on the Mersey. To build such would only end in disappointment, and a wet jacket, if nothing worse. Also, paddle-wheels are quite inconsistent with such a small boat, even for smooth water.-MERSEY. [45232.]-Speed of Boat Engine.-Now you have given me some idea of what you want. As it is a paddle-engine you are thinking of, the engine, 24in. by 5in. would do, although it is somewhat small; therefore you won't get much speed. First, let me say that you must not expect more than very little speed-say about four miles an hour. The boiler you name is not at all suitable to the case, but if it has an arrangement to carry the fire in-a casing lined with fireclay-you might do something with it. In that case you would want a grate 10in. by 12in. long. But even of chimney. It should be 5in. diam. and 5ft. or this wasteful size depends on the area and length size nozzle. If everything be properly arranged, 6ft. long, with the exhaust thrown in with a goodsuch a boiler would keep 30ib. of steam well What I should enough for a paddle-engine. advise you, if you have not got too far on with the boat, is to have a larger engine and boiler, and let the latter be either a vertical or horizontal, with internal furnace tube. Is there anything else you want to know ?-SUNLIGHT. [45264.]-M.R. Express Engines. - The 1472 class have driving and trailing-wheels (coupled) 6ft. 8in. diam., and cylinders 18 by 26. Their other dimensions are similar to the general ventor of it is Mr. H. J. Dale, 4, Little Britain, Whistle or Bell.-If, on the next opportunity. type of M.R. express engines. Their Nos. are 111 London, E.C. It is not a patent.-LANCASHIRE. [45132.] Change in Pitch of Railway Mr. Tuttle will carefully observe the phenomenon he refers to on p. 308, he will find that the pitch does not "gradually go down" but drops suddenly, just when the bell passes the listener. The gradual decrease in loudness of the sound as the bell recedes, is apt to lead one to think that the pitch is decreasing, but theory and experiments agree in showing that the pitch varies with the relative motion of the two trains, and not with their distance apart.-J. BROWN, Belfast. 1472-1491. The 1492-1501 115, 1400-1409, [45287.]-L. and N. W. Railway Goods and Mineral Engines.-In answer to Iron Horse |