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DIAMOND ROCK-BORING MACHINE AT THE CROESOR SLATE QUARRIES (described ou page MW).

TO MILLERS.

Sir,—In common with others of my profession, I ImV»- watched the discussion in your columns on the subject of mill-stone balancing with much interest; nevertheless, it is by no means clear to me that the subject has been satisfactorily disposed of, either in favour of the supposed perfect unity at all times of the standing and running balance, or in favour of the other position—namely, that the standing and running balance are not necessarily identical, but may vary under certain circumstances.

It has always appeared clear to me that, with the present construction of mill-stones, it is theoretically impossible to secure perfect unity of both standing and running balance—that they should exactly coincide— because the size of the "burrs" is never the same precisely; and, to satisfy myself more thoroughly, I reported to the following simple experiment, which occupied only a few minutes, and if repeated by my brother millers, I feel convinced they will tind in it an explanation of the difficulty :—Procure a rectangular piece of wood, of a shape similar to that indicated in the annexed sketch (say 5in. long by lin. square) A В.

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Tais is hollowed in the middle to receive an upright support- say the top of a pencil—E, slightly impressed into the timber to make balancing the easier. On either end, one above and one below, as in the drawing, is fixed a piece of lead or other heavy substance (a quarter-ounce weight will do if well tied ou), of equal weight, C, D. When the whole is balanced nicely oe in the illustration, the timber is supposed to "* perfectly horizontal. Now begin gently to blow with the breath at one end, so as to cause the timber to

revolve, when the end A will be depressed and the end B elevated to a considerable distance from the original horizontal position, in obedience to the law of centrifugal force, by which, of necessity, the heaviest portions of the outside extremes of a revolving object tend to the furthest point from the centre of rotation.

The application will be obvious. Suppose the timber to represent a section of a millstone, and the dotted lines surrounding A and B the burrs ; now these are of much greater specific gravity than the plaster which covers them. The one (A) is much deeper than the other (B), and therefore nearer the top—the one B, is thinner, and nearer the bottom; therefore the centre of gravity of A is at a little distance above that of B, considered in relation to the horizontal. Burr A is, therefore, represented by the weight C, and burr B by the weight D in the experiment, the timber representing the plaster of the stone; the difference being that I have purposely exaggerated the proportional distance between the relative positions of the centres of gravitation of the heavy part of periphery, in order to make the principle clear; which principle is in no way affected by being presented in an exaggerated form, because, whether the vertical distance between the centres of gravity of the burrs at opposite sides (considered relatively to the horizontal) be 2iu. or 2ft., the disturbing cause is the same per »c namely, the influence of centrifugal force, as before mentioned.

If I have made myself understood, I think it will be apparent that a standing and running balance may not be identical under all circumstances.

[11] F. Davis.

CAPE HORN, GOOD HOPE, AND PORT JACKSON.

Sir,—One of your correspondents, "M.L., "has computed by spherical trigonometry the distances between these three places, and is desirous of having his results verified. He makes H G - 4,105 miles, c, J = 0,824 miles, H J — 5,831 miles [see page Ö3iij. I was induced to try them at his request, and I make the results somewhat near, but not exactly. This may possibly arise from not taking the same latitudes and longitudes. The way I proceeded was this: I made the triangle

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with prepared chalk on the globe, and found that tit« complements of the latitudes, and the differences of longitude were as follows: P H = 84= P, P G = 55° Об-,

P J = 66* 8-, these form the sides of t he three triangles; then the angle H P G m 85- 49', G P J = 182e 45', and H P J = 141° 27. Thus we have two bides and the included angle, and the question is to find the third side. Perhaps some other of your correspondents might bring the figures nearer to " M. L's." results. I am not mariner, nor have I, at least for some time, had an opportunity of meeting with any one who has computed the distance by sea, but I should imagine the course H J could not be accomplished, the route being too near to the south pole.

By the bye, sir, as you have invited letters on summer pastimes, would not one of your correspondents give us a few remarks on the art of swimming, so useful both to mariners and every one.

T. S. H. P.S.—I make HG = 4,032 miles, G J » 0,794 miles, and H J - 6,838 miles.

[13]

FLUTE FINGERING.

Sir,—A correspondent complains of the bother of flute fingering in extreme keys, by which I suppose him to mean the flat keys. But is it possible, in t he ■■ days of sliding heads, that anybody submits to the bother of making the flat notes independently as they come? Supposing your correspondent has to accompany a piano, the music being in 1 > flat, he should, by means of the slide, tune his D to the D flat of the piano, and then play the notes as though they well- written in the key of D, with two sharps, which is the natural scale of the flute, and causes no extra fingering "Imtever. Exacl ly the same sounds will be emitted as if he hod elaborately flattened each note ад it occurred. The reason is evident—by drawing out the slide he flattened all seven notes. Bat the staff directed him only to Hatten five, B, E, A, D, and G; therefore he has to sharpen the other two, F and C. For the aame coose, with the flute so adjusted, six flats is to be played in one ibarp, four flats in three sharps, three fiats in four sharps. It may appear to the uninitiated as if it would be easier to play in three flats than in ¡our sharps, but it is not io, for in the ârat case С and F пате tobe made natural, making, with the signature in the stuff, fire notes to alter; in the latter case there are only two io alter, the other two being in the scale; only in Doing this mode an accidental flat must be played as a natural, and an accidental natural as a sharp, because the natural note is flat to the sharp, and sharp to the flat. With a eliding head a flute requires but four keys, the D sharp, E sharp to make F natural, the G sharp, and the A sharp. AU others are mere surplusage. If the music leave the flat key for а п.it tirai without there being an opportunity for fresh tnning, make before starting a nail mark on the tube at the length for the natural note: the compoeition with which it is mode to go smoothly will take it. I hope these directions nxav bring some relief to perplexed fingen». T. S. G.

Г18]

THE LUNAR CRATER—» ALPETRAGIUS D." Sib,—Mr. Michell Whitley, of Penartli, Truro, a very •aref ul observer of lunar objects, has addrossed a letter OB the editor of Scientific Opinion (see No. 85, June 15, 1«70, p. 238), containing his observations on June 8, 1870, of the spot "Alpetragius d," (not the Greek Delta -^printed, but the Roman d), in which he speaks of a minute blow hole in the centre of the white spot now occupying the place of Beer and Madler's crater. lam not aware of anything having been published on this spot since my article in the Student, referred to by Mr. Whitley; bnt at the close of 1868, aud in the spring of I860, I received communications on it from the wellknown observer Mr. Knott, of Cuckfield, and shall feel obliged if you will kindly give publicity to the following extract from his letters :—

M December 24th, 1868," Mr. Knott вазт», " I hasten to report to you the result of an examination of 'Alpetragius d' last evening, which adds one more to the points of resemblance between it and our old friend Linné. Obaerving with my 7¿ in. Alvan Clark refractor and a negative eyepiece magnifying 424 times, I detected on d (which appeared as a bright soft edged spot) a minute craterlet, with a diameter barely one-half that of В and M's little craterlet on the south. This is evidently the same object as is figured by Lohrmann on his unpublished plate (see Student, "vol. ii., p. 48,

Slate) referred to by Schmidt." On February, 20,186У, tr. Knott again examined this region, when he distinctly saw the craterlet as a crater, and estimated its diameter as equal to half that of В and his little craterlet on the south.

It is exceedingly gratifying to find three such observers as Schmidt, Knott, and Whitley agreeing во closely with regard to this spot, all three placing В and M's little craterlet on the south edge of the white spot, and the last two finding an exact resemblance to Linné in its three main characteristics, as observed since October, 18664 I hope many of your correspondents will often turn their telescopes upon it, that these features may be closely watched. It is situated to the east of the two undesignated craters eastward of No. 205, on Webb's map; the largest is Alpetragins d of В and M, the smallest B. The colour of the interior of В is darker* than given by either Lohrmann, Beer and Miidler, or Svhmidt.

Your correspondent Albert P. Holden will find recent estimations of the distance of Xi Ursre Majoris by ЛХевягк. Whitley and Ingall, in the above quoted numi>er of Scientific Opinion.

W. R. Birt.

Cyntliia Л illa Observatory, Walthamstow. [14] 1

BICYCLE RIDING. MEDICAL OPINION WANTED.

SiB,—I wish to ask a favour of some of your medical readers, and though it is like a sort of consultation gratis, yet, as it is a question of universal interest at the present time, it may not be considered asking too much.

Several individuals who have never "risked their necks" on bicycles have occasionally grumbled at the many letters respeeting such machines; but I am sure not one of them would object to space being given to determine whether their use is, or is not, injurious to their numerous riders, and whether the strain on the abdominal rings is or is not so great as to cause ruptures, àc.

I am aware that a letter appeared about this some six months ago, in your columns; but there was only one reply, and surely on sueh an important question as this we ought to have a more general opinion. I have heard that in five years it is considered that a bicycle rider would be completely ruptured with daily practice. I of course cannot vouch for the truth of this myself; but I had it from medical quarters. What a calamity it would be if, in about that time from the commencement of bicycle riding, all those who frequently used the machines were served in this way. I therefore request opinions on this important point, with the editor's permission, and also, whether the use of a broad band round the abdomen would be sufficient to prevent such consequences. Perhaps, also, velocipedes which drive by levers with a horizontal motion may be free from this objection. It would be well to know this, and if they are not, the only safe velocipede would be one prepelled by the hands.

[IS] S. Jamks.

SEWING MACHINES—REPLY TO "GROCER." Sir,—That a Thomas's shuttle will work best with the thread unwinding from the under side of reel is well known. The instruction books teach it. I have not recommended the reverse, and although the drawing shows it reversed, it was done intentionally, believing it would be easier to comprehend so illustrated. Thus far I beg to thank "Grocer" for pointing out the error, but entirely disagree with him as to making the "spring long enough to catch the brass end of shuttle reel." Firstly, in practice the brass end of a shuttle reel is usually far from being a true circle. Secondly, the spring pressing npon an irregular form must give an irregular tension. Thirdly, if the brass end of a shuttle reel had a true circular form it would be inferior to the short spring te give a regular tension. Fourthly, because when the reel is full of cotton it pulls off easier than when it is nearly empty, owing to the difference between the diameters. When full, the diameter being largest, affords a greater leverage to turn the reel when the cotton is pulled off. A full reel of cotton or thread presses strongly against the spring, and resists strongly the palling off, but as the diameter of the thread diminishes, so (A* resistance of the spring diminishes, and !Ji и в compensa te« for the irregular action caused by the using, and diminishing the diameter of the reel of thread. It is, therefore, far superior to a constant uniform pressure of the spring ou the brass end of shuttle reel, which cannot compensate for the varying strain on the shuttle reel üben nearly full or empty. "Practirol Man" recommend« a short spring, as represented, to any one who would make a shuttle for himself (but it is far more economical to buy one), and further recommend л the kind of reels to their respective shuttles, as illustrated at page 167. "Grocer" is in favour of a Singer reel, *' because if the reel is not pressed firmly down (in the Thomas's shuttle) the hinge goes behind the end of the shuttle reel and shuts it out, instead of in." If "Grocer" found this to be the case tiro or three times with persons he sold machines to, what would he expect to find if he applied the Singer reel to a long shuttle, or a No. 1 Thomas for shirt collar work, where the best stitch is required at the highest speed? The latter part of "Grocer's" remarks will be best replied to by the description and illustration of machines about to appear in a systematic manner; and nothing could be more unfortunate to those who seek a thorough knowledge of the subject, than to introduce haphazard the whole or part of certain sewing machines of doubtful merit, or to use valuable space merely for advertising purposes without pavment. Л Practical Max.

[16]

VELOCIPEDE CONSTRUCTION.

Sir,—Each maker—amateur or otherwise—seems to me to judge of his and other machines by the rate he can go on it. Now I think that is an erroneous test, for I saw a machine, horrible in appearance, construction, aud principle, propelled at as great a rate as thirteen miles an hour (which for tricycles I believe to be the maximum rate), only the driver was a strong swarthy fellow, a^d exerted his utmost. It is therefore not to bo wondered at that " A Pattern Maker" should think " the whole etoek of velocipedes up to nothing when put really to practical work, and particularly in a hilly district." After describing a veloce the usual finis is "that it can be made to go fifteen miles an hour with ease," which, by my criterion, is folly. I grant that these machines can be made to go at that rate, aud uphill, but it is practically " no go," I have practised the bicycle for a year in a hilly district (compared with many in England a very hilly one), and can keep my saddle over most of the hills without difficulty, but the labour is excessive. I would judge of a good machine by the "ease" required to propel it eight or at most ten miles an hour, to gain which lightness, combined with simplicity of construction, height of wheel, india-rubber tires, and yielding springs are tho necessary things. Loose aud light clothing is also very desirable for summer riding. But in my opinion, to rattle over the ground at the rate of one mile in four minutes on any but a first-class machine with even roads is sheer folly, and undoubtedly more so with a tricycle than a bicycle. One of the chief ingredients of pleasure is ease, I take it; and as veloces are at present used chiefly for pleasure, the further we exceed ten miles an hour so much do we lessen our pleasure.

Another thing that I am sceptical about is the common dogma that the driving wheel ought not to be more than 8Gin. or iWin. It is being continually brought forward in the Mechanic, yet to my knowledge has never been discussed, but seems to be qnictly swallowed by brother readers. The little 8. James (page 80ÍI) says on the two and three wheeler is very correct; but I don't see why tho driving wheel should not be as large as the leg will admit of. If, however, auy one will be kind enough to "show cause why" I should believe the common dogma he will very much oblige. Husband,

[17]

UNFAIR CRITICISM.

Sir,—It may seem unwise to refer in the pages of the most widely circulating scientific journal in England, to adverse criticisms in a contemporary of minute circulation. But I look at the matter in this light. Professor Pritehard has chosen, in reviewing my "Other Worlds," to make certain charges against me in Nature. If these charges are true they ought to be more widely known than they can possibly be while confined to the columns of Nature; if they are not true my countercharges ought to be moro widely circulated.

I deliberately assert that Professor Pritehard has written a more discreditable review than any which the veriest hack-critic would have penned. I have no doubt, as I have written to him, that he is "bv this

time heartily ashamed of the paper;" but unJortoaateh justice requires that I should take further nottce of hii indiscretion.

I pass over his remark that he cannot follow my reasoning in a certain chapter, with the simple eoniment that from Sir J. Herschel (who has done me thp honour of indicating special approval of thie very chapter) down to the least instructed reader, not eme I venture to assert has fonnd any difficulty in master u. ■■ the reasoning, save only the Savilian Professor of Astronomy.

The gravamen of my charge rests, however, on hi> assertion that "Laplace, the elder and the yoocger Herschel, Humboldt, Admiral Smyth, Sir WiUiaxo Thomson, Mr. Tait, Dr. Balfour Stewart, Professor Tyndall, and other honoured names, all in their torn come under Mr. Proctor's advene criticism, with greater or lets severity." This assertion is inexact If the remark that one does notagree with this or that opinion of such and such a person, be rightly described as "criticising that person with severity " then I um opee to Professor Pritchard's charge ; if not, then there i« no truth in it.

But a typo of my severity was wanted, and Profesor Pritehard, with as much dexterity as though hie trade were hack-reviewing, conveniently makes one. There h one sentence, which, taken apart from the context, sounds severe. Whewoll had spoken of Jupiter as a watery globe with a few cinders perhaps at its centre. I remark in "Other Worlds," that sarely " no astronomer worthy the name " can regard Jupiter as it wa¿ thus regarded "by one who, be it tJuAkfullv remembered, was not an astronomer." Buttheulgoon to indicate in what sense I use the word astronomer. "Ее" I say, "who has not gazed hour after hour on Ibegln;,. of the giant planet,"&c. Every one knows that Whe^vt U was not an astronomer in the sense in which I wrote. For the larger portion of his attention was directed to quite other matters than astronomy, and it ia simply true, as he himself admits in hi* "Plurality of Worlds' that he was not, properly speaking, an astronomer. Fortunately I have spoken with far too obvious a«mciation of Whewell'e wonderful abilities for m I meaning in this passage to admit of being misinterpreted by others than Prefessor Pritehard.

Professor Pritehard then goes on to say that I Attack Mr. Lockyer's views about the corona "simply because they do not square with mine." He know perfectly well why I attack them; fori assign very deanite reasons tfttuwe

He would not venture io assert that tho** reasons are insufficient, because, if he did, пвтц|Д Inn all title to be regarded as a mathematician.

Equally clever is his quotation of a passage having reference to the theory of the meteoric origin ol solar heat. I write "I am quite certain that there is no flaw in the evidence I have adduced from the laws of probability; and that," &c. But it suits Professor Prttchards purpose to make it appear that I am only expressing over confidently a mare opinion—so he quietly drops all reference te the evidence, aud makes me aay, "I am quite certain that at least an important part of the sun's heat, &e." He immediately adds, "wemay fairly ask whence has Mr. Proctor this certain knowledge," &c. Yes; but if he had quoted the sentence in full, it would have become unpleasantly obvious that one had only to turn to "Other Worlds" to find out whence Mr. Proctor derived his convictionIt is well known that Mr. Lassell, the eminent and skilful astronomer who is the present President of the Royal Astronomical Society, considers that Uranos has only four satellites ; for he can see but four with his splendid reflector at Malta. "How then can Mr. Procter," asks Prof. Pritehard, "venture to set his opinion " (that there are eight at least) "in antagonism," &c, Ac. How indeed? But suppose Mr. Proctor wrote thus—" Four of the satellites discovered by Sir Wm. Herschel have not indeed been yet identified; but one cannot read the account of his method of procedure without feeling that no amount of mere negativo evidence can be opposed effectively to the positive information he has left us respecting these four orbs." Does not this somewhat alter the aspect of matters?

Then what am I io think of his quoting a printer's blunder (obviously so from the context) as only probably an inadvertency? On page 41 of my book are tttMs words—"a glowing vapour gives n spectrum of white linee," where it should be "bright lines"; but within a few inches, on the same open paging, are these words—" They tried the spectra of glowing vapours, and .... they found bright lines of vnrious colour." He then goes on to speak of " an alleged breaking of a dark glass " where I have spoken of no such event as having actually happened; and somewhat spitefully add-— "these (two) misstatements are easily corrigible in a second edition, presuming that they are not typical of much else in the volume itself," from which we may fairly conclude that Prof. Pritehard had not read the volume, and was therefore hardly in a position to criticise it.

I am sorry to have to comment severely on Prof. Pritchard's conduct in this matter. I cannot at all understand why he should be irritated against me; but it is clear to me that nothing but tome irritation could have made him so forget himself. J1 I had attended the meetings of the Astronomical Society when he was president, I should imagine he gave me credit for some of the anonymous attacks which were so freely made on his school-masterly reading of the part of President. But I was not. A year ago I had occasion to remark at one of the meetings of the Royal Astronomical Society, that in commenting on a paper of mine, he had "begged the whole quest i uu" at issue; but ■-m.lv so small a matter as that cannot have anger«? J him for a whole year. Taut ш, àc.?

[10] Richard A. Pnoctos.

INDIGO.

Siu,—The samples of indigo which I have had the pleasare of sending yoa were extracted at Accra, on the west coast of Africa, from a species of plant known н~ Indigofera. Tikis plant grows in great abundance on the west coast, more particularly on the Liberion or grain coast, where there is great quantities. Merc haut-, who trade to the coast seem to have entirely overlooked the benefit to be derived by the cultivation of this valuable dye. Several important things have to be oheerved in collecting the plant fit for fermentation. The modus operandi is similar to that which I have earned oat in the East Indies, excepting that the maceration is useless in this case, and that the fermentation takes about 26 hours. The indigo when precipitated has a greenish tint, which may be destroyed by being boiled with one part S On to 30 parts of water, which entirely destroys the chlorophylle (which gives it that tint), and renders it similar to that which I have sent yon. Market value of the dye at the present moment is quoted to nie by one of the tirst tinusin thy trade at 7s. bo. per lb.

I hope to have the pleasure of submitting to yon samples of cloth manufactured by the natives of Benin, and dyed with the indigo.

R. F. Garth.

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ELECTRICITY. — PARALLELOGRAM OF
CURRENTS.

Sir,—I am anxious to obtain information on some matters connected with electricity; and I write to yon in hope that " Sigma," or some other of your correspondente, may afford me the information I desire.

It is well known that magnetic currents in the same direction attract one another, while those in opposite directions repel one another; and also, that currents converging to or diverging from the same point attract one another, so that if Л tí, С U, Fig. 1, be two similar wires, along which currents of equal quantity are passing, and which can move freely about their middle point O, they will swing round into the position

0 X, where О X bisects the ¿ Bo D.

Now I wish to know if these facts have suggested to any experimentalist the idea of a parallelogram of currents, analogous to the parallelogram of forces or of velocities.

I have neither the time nor the skill to make each delicate experiments as would be required, myself; but

1 will state what I conceive would be the enunciation of auch a theorem, and I should like to hear whether my statement represents an established fact.

This then is my ideal statement.

If two rectilinear currents cross one another, and a magnet or solenoid be placed so as to bisect the »hortest distance between the two, it will take up a position as though it were acted apon by a mettant cur г ont, whose quantity and direction may be estimated as follows :—

Let A*, By, represent the directions of the currents, and let AB be the shortest distance between them. Bisect' ABinO, and draw О X, O Y, parallel to Ax, By, making, О X: OY : : quantity of electrieity passing along Aar : quantity along By.

Complete the parallelogram X У; then O R will represent the resultant carrent in direction, and its

Quantity will be represented by Ü1? r «. AB

In the fignre the magnet is supposed to be placed at 0, and if the theorem be stated correctly the magnet would take up a position at right angles to 0 R. П this were found to be correct by experiment, the theorem would be proved as regards the direction of the resultant: to prove it as regards the quantity of the resultant would require a delicate galvanometer

Í20J R. P. S.

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AIR PUMP.—INDUCTION COIL.

°1R»—I beg to thank the two correspondents who have

answered my inquiries about the Air Pump ; though, as I

feared, they have not given mc any information beyond

what 1 already knew. The first one has eimply given

a description of Tate's pump, a form well known; the

other describes nothing more than an ordinary ex

fîuTM8 ajrinee' which, I have ascertained, is sufficient

l« the vacua required for the experiments mentioned

Itb* TM my ^tter, bok utterly nseless for higher vacua.

1 thought, among your numerous correspondents, there

might be some who have gone in for the subject in its

higher branches, and who could and would give me the

result of their experience.

What I want is a pump that will produce a vacuum eo*n*j » »bout one-twentieth of an inch of mercury, and I know that the expensive class of pumps sold for this purpose—and they are indeed expensive—are made with a single barrel. It was the construction of one of these that I wanted to elicit from some of our scientific inends. There is a plan of Grove's called a repulsion PïmP,Ktnat I bave read about, which I believe is very good, but I do not know the particulars sufficient to work by. I am now constructing one on my own plan, íuí Which l ш raUier eaaguine; still I shall be very 5JKTM* for an>* aaeful information on the subject. и i reeEn* *° *Ь* induction coil mentioned by me, I 2*P be TMry glad to give a full description of its construction if yon, sir, think it of sufficient interest; or I will give it personally to any inquirer if they write to l°°у? тУ address. I have had the opinion of a celebrated electrician on it, and he tells me it is a marvellous success. It is constructed on the vertical plan—so far

there is nothing original about it; it only remains for me to describe the method of its construction, which is peculiarly simple. I have about the same weight of secondary wire as that mentioned by A. Farquhar; bat as my wire is No. ¡16, I have a much greater length. No. 29 is too largo to produce length of spark, though, with proper i[i -.illation, it ought to give great density; but, in my opinion, it is much too thick. Mr. Farquhar may find his coil, with its imperfect insulation, answer with small battery power; but I caution him not to try foor or five cells, or else he will find it come to grief; for cotton covering and shellac varnish is quite insufficient, even when constructed, as I présame his is (for hie description is not at all clear) on the vertical method. My coil, with one cell, the platina about '2im. by -tin., gives a good dense spark at Uin. surrounded by a thick aureole; and the spark I get at from Sin. to 4in., is sharp, bright, and zig-zag, not straight and thready. I have tried it with a mercurial break, but I cannot get nearly the same length of spark as I can with the vibrating spring; the cause of this I am unable to comprehend, not having hod any experience with this form of break.

In conclusion let me advise those who are thinking of constructing a large coil, not to think of the old horizontal methods with gutta percha insulation: they are a delusion. I do not say they cannot be made, because they have been and are ; but they are always likely to break down, and then they are done for. While on my plan they cannot break down, and much greater results can be obtained with small battery power, which I consider to bo one of the great desiderata.

Ind истомим.

Bl]

TRADE AND COMMERCE.

Sir,Ah "Herbert" has written you a third letter before my answer to his second one appeared, I must again trouble you with a few lines in self defence. I have got "Herbert" into a little corner; and although he fights fairly and manfully, I cannot make up my mind to let him out until he proves his case, or acknowledges his error. He assumes that trade is barter, with the corollary that the balance of imports over exports is profit. Upon this point he must stand or fall. I have endeavoured to prove the contrary, and cannot consent to accept as an axiom that which is really the point in dispute. It is in vain that he builds elaborate edifices upon this basis, until he prove that it is a sound foundation.

At page 30G "Herbert" says that even I (F. W. M.) can see that when a foreign-made article is purchased, part of the money goes to the foreign workman, but that I cannot see that some foreign gentleman paye an equivalent sum, which comes into the pocket of an English workman. My inability to see this does not arise from shortsightedness. In the well-known play of The Critic Tilburina was not to blame because she could not see the Spanish Fleet—her failing, which called forth the rebuke, was that she professed to see it when it was "not yet in sight." The case would be exactly as "Herbert" states, if trade were barter, and trade were free, but the first condition is disputed—the second unfortunately does not exist. The real state of affaire is just this :—The foreigner, having received £29 for his goods, is willing to spend that amount upon English manufactures, but his government has laid a restrictive duty upon these ; and if he bays them in spite of the duty, his £29 goes somewhat after this fashion, £18 for English goods, and £11 to the State for doty; so that the Englishman gets but £18 back against his £29 expended and sells but £18 worth of goods against the £29 worth that he bays; or, to extend the example so as to embrace the whole of the foreign trade of the conntry, England bays from the foreigner £294,693,608 worth of goods yearly, whilst he is unable to buy from her more than £179,077,812 worth in return. "Saul Rymea" may well ask "What sort of prosperity does thiB indicate?" "Herbert" is fond of similes. I will give him one as a counterblast against his "cargo." Suppose the nation to bo a business firm which buys and consumes every year £29,000 of goods and manufactures, and eells but £18,000 worth. Is this firm doing a profitable business?

Last week there was a discussion in the House of Commons on the subject of "Unemployed Labour," which was very interesting, although unsatisfactory in its result. We may, according to our several prejudices, believe, with Mr. Torrens, that the country is in a state of destitution and misery, or with Mr. Goschen, that it is prosperous and happy ; but above all differences of opinion, beyond all contradiction, looms out the damning fact that the nation is unable to sapport its people.

There was a time when increase of population brought with it a corresponding increase of work, and the nation was stronger and more prosperous in proportion to the increase. All this is changed now, and it is a suspicious circumstance that the change should date from the period when, through the influence of Free Trade, our imports have commenced to be much in excess of our exports. Some of your correspondents regard the necessity for emigration as a proof of oar prosperity. It is an unfortunate time for a nation when the symptoms of weakness and disease are looked upon as proofs of healthiness and strength—when the hectic flash of consumption is mistaken for the rosiness of health, and the nation disports itself in a fool's paradise, unconscious of the disease which is destroying its constitution.

We have had five-and-twenty years' experience of the working of Free Trade, and ought now to be in a position to judge of ils effects. A Government Com mission, appointed to investigate the subject, could not fail to bring to light many interesting and instructivo facts, but there is little chance of such an appoint

ment. The great apostles of Free Trade—those who persuaded us to shut our eyes, throw open our ports, and see what fate would send us, have made an enormous reputation thereby. By the majority of people they are worshipped with a devotion which does not fall short of bigotry. Any attempt to question the infallibility of their wisdom is at once drowned with cries of derision. Their followers are as certain of their case, and as intolerant of opposition, as were the opponents of Galileo in their belief that the sun revolved round the earth.

Were it once proved that their commercial policy was wrong, these greet men would be in danger of losing the vast reputation they have acquired; and although we mast credit them with every possible honesty of intention, yet as every one sees things through spectacles more or lese coloured, it it possible that such a consideration as this might deepen the couleur de ros« of their spectacles suihéienxVy to conceal from their vision the blnenese of tint which is slowly bat surely overspreading the aspect of ntfairs.

{.221 F- W. M

SEWING МАСНГДЕ8
f Continued from page 281 .J

Sir;, -lu a shuttle lock-stitch machine tbsrc are four primary, continuous, and essential motions for making the stitch, and three adjustable or moving parte to regálate the stitch. These may be clarified м follows:

1. The Needle Motion.

2. The Shuttle Motion.

3. The Feed Motion.

4. The Main Shaft and Driving Wheel.

The first three motions are not uniform, either separately or combined. Attempts have been made to obtain uniform motion to prevent noise, or for some supposed advantage, but such changes from the correct motions entail certain disadvantages.

The machine must be fitted with

5. The Tension.

ti. The Thread Take-up.

7- The Stitch-screw or Regulator.

Some machines require, in addition, other parts, as a Presser and a Lifter, when the under-feed is used.

The usual terms will be used in the description of sewing machine*, so far as practicable; but to prevent confusion when comparing them, certain changes are necessary. For example, it is usual to speak of the frame or bed on which the shuttle slides, as the shuttle race; this bed being immovable it is not appropriate to apply the term race to it. By using the term shuttle path, it will apply without confusion to a straight, curved, or oscillating shuttle movement, either slitting or carried.

To the courtesy of the Howe Machine Company, of 64, Itegent Street, London, wo are indebted for the following illustration of the first machine invented by Elias Howe, jun., the late president, who made many kinds of clothing on it at the rate of 90Q stitches a minute. The idea of this invention was worked out in a rough model of wood and wire, in October, 184Í. In July, 1845, he sewed by his first machine the seams of two suits of woollen clothes. In 1867 the same machine was displayed at the Paris Exhibition. A model of it may be now seen at the Museum of Patents, South Kensington.

It is not a little perplexing to find the invention of the sewing machine claimed for France, and a tailor the inventor, who had many of his machines, in 1841, making army clothing.

The mob, it is stated, in the Revolution, ruined the establishment in which the inventive tailor had ashare, and sent him to die at Amplepius in great poverty.

If there be a shadow of truth in this ¡statement that army clothing was made by a French sewing machine four years earlier than Elias Howe's successful working of his machine, surely we ought to have sufficient evidence of so important a fact. Are our neighbours in France so careless of the reputation of their countrymen when most deserving? Is it wise to bestow so much glory on war, and leave the hero who conquers in the arts of peace to die in poverty, unrecognized?

If the story of the inventive tailor will bear investigation, wo appeal, as " English Mechanics," to "French Mechanics," to perform their duty, and let us have the particulars of the machine, that it may be illustrated in our "English Mechanic," and duly honoured. If the story be a myth, let it be dealt with so that it may not be further circulated by being copied in the public press as an established fact.

A close inspection of Elias Howe's first machine will show that he embodied all the essential movements. An eye-pointed needle passed the thread from a reel through the fabric, then the needle loop was formed, and the shuttle passed through it, the needle being pulled out of the fabric and the stitch tightened, when both needle and shuttle came to the end of stroke; the feed then advanced the fabric the length of stitch, the shuttle travelled back, and the needle again penetrated the fabric to make another stitch. In the illustration it will be seen the fabric is placed vertically on pins, the pins being connected to a rack plate which moved a given distance, stitch by stitch. When the rack had travelled its full stroke it had to be plaeed back to commence afresh, the fabric being at the same time readjusted on the pius. This feed motion appears now very awkward. It was used in other machines in the early attempts; and I have seen a rack, and the bed of the machine, a yard long, so that one yard could be stitched without stopping to readjust the feed.

All the essential motions were transmitted from the main shaft, on the end of which may be seen the driving wheel, behind the fabric and above the machine. On the main shaft may also be observed the cam, having the same kind of action as that attached to the SEWING MACHINE.

[graphic]

modern Howe machine, an illustration of which will follow, and prove to satisfaction thnt Elias Howe deserved all he received of wealth and honours.

Errors In Illustrations.—At page 281, Fig. 4, the spool case is represented resting on the end of the upright shaft g. In such a form the needle thread would not pass between the spool case and its bed. The surface of the spool case and its bed should be as -mouth as possible to allow the thread to pass in the manner described. At page 157, Fig. 9, the thread is represented passing over, instead of under the reel. It works much better under the reel, bnt may not be so clearly understood by the thread being hid below the reel. The shnttle should be made in all respects as represented in the illustration, Figs. 9 and 10.

A Practical Man. [23]

HOW TO TRISECT AN ANGLE.

Sir,—I have read with interest the letters of yonr correspondents, F. C. Penrose, June 24th, and "O. H. S.," June 3rd, on the subject, "How to trisect an angle."

May I suggest to them the following, which appears to me a solution of the problem? If I am wrong perhaps they will kindly set me right.

[graphic]

Let A PB be a cycloid. L P К any position of the generating circle. Draw P Q M parallel to the base В С. Then A Q is any arc.

It is required to trisect it.

Take T C, one third of L C, and draw the generating circle in the position T S P, and draw p n q m parallel to base.

Now PN = QM ... PQ = NM = LC

AndLO» ВС -BL = 7T - arc PL = arc P К = arc AQ

.'. иге A Q a LC = 3 TC = 8 nm = 3 p q = Загс Ад

By which means any arc of a circle may be divided into any number of parts. R. T. B. R.

24]

TOURISTS' TRIPS.—NORTH WALES.

Sir,—I have read with great pleasure several letters in the English Mechanic on the subject of " Tourists' Trips," and I am very glad to see that there is evidently a growing taste in several, for thoroughly seeing the beautiful scenery which abounds in our own country, in preference to taking continental trips. It has occurred to me that an outline of a walking tour undertaken by me, through a part of North Wales, might be acceptable to the readers of the English Mechanic. From Llandudno to Conway, four miles, thence to Bangor, fifteen miles. From Bangor proceed to Beaumaris (only a short distance) by way of the ferry, and then on to Carnarvon {vid the Menai Suspension Bridge), passing on the way the Menai tubular railwaybridge. While at Bangor, the tourist should not fail to visit the Penrhyn blate-quarries, distant six miles.

From Carnarvon a walk of ten miles brings the tourist to Llunberis, and he then has an opportunity to ascend Snowdon. A capital way of doing this is to ascend the Pass of Llanberis, and climb the mountain by what is called the Capel Curig Path, descending on the opposite side to Beddgelert. Here the tourist has a choice of roads, and the way I chose was on to Capel Curig, a distance of nine miles. While at Beddgelert, visit the pass and bridge of Aberglaslyn, and at Capel Curig the falls of the Ogwen. From Capel Curig to Bettwe-y-eoed, and thence to Llanrwst. Here the tourist may complete his tour by walking to Conway and. Llandudno, thus completing the circle, or he can extend his tour in the same manner I did, by going on to Denbigh, St. Asaphs, Rhuddlan and Abergele, calling, on the way between the two latter towns, to inspect the beautiful church at Bodellwydan.

This tour occupied me about nine days. It would be impossible to enumerate all the objects of interest along the route, but the tourist should provide himself with a guide book, in which he will find interesting notices of every object worth mention.

Several of your correspondents en! quire the most economical way of doing a trip; I should suggest to them to stay each night at a good hotel, breakfast there, and then, during the rest of the day, eat and drink when they require it, and where they can get it. Another plan is to take cheap private lodgings at some central town, and from thence make day excursions through the surrounding district. If they wish to do it very cheaply, they must cater for their own eatables, &c.t 4c, and take a good supply out on each excursion. In the course of a month, I intend taking a walking tour in the lake district of Cumberland and Westmoreland, when I expect I shall adopt the former of the two methods I recommend, with the addition of a good dinner at an hotel each day. Should any reader of the English Mhchanic be disposed for such a tour I shall be glad to hear from him, with a view of going together. I have not yet met with a companion, and I think it decidedly pïeasanter as well as more economical for two to travel together. My object is merely to enjoy the scenery, 4c. I am no artist, botanist or geologist, but an ardent admirer of the works of nature. Should any one similarly disposed address me as below, I shall be glad to give further particulars.

Bonington, Spalding, Lincolnshire. B.

[25]'

TOURISTS IN SCOTLAND.

Sib,—The many readers of your scientific columns seem to be panting for a little recreation to their mituU; and no doubt not a few of them meditating a tonr, are desirous of knowing where to go. It is a well-known fact that Englishmen are more given to admire the beauties of other countries than their own, or rather, neglect these to attend to others. I have met with men who have been round the world who have never seen the famed Scottish lake-scenery, though born within thirty miles of it. In Scotland our всепегу is in many parts very fine, and those of your subscribers who have travelled in many lands without visiting it, will, I am certain, find it compare favourably with other countries in this respect. The Highlands of Perthshire, are, I can conscientiously say, a very charming retreat for the summer months, and to those who are from mouth to mouth shut up in smoky cities, will be found to be all that I have stated. I may mention a few towns where capital and suitable accommodation can be had either in hotels or lodgings—viz., Crieff, Dunblane, Blairgowrie, Pitlochrie, and Dunkeld. The drives around Crieff are тагу lovely; and those who are advocates or lovers of the water-cure, will find a fine hydropathic establishment convenient and healthy. At Dunkeld, the wooded scenery is said to be the finest in Scotland; and the tourist in the summer months can get a fourhorse coach running thence to Braemar, via Blairgowrie and Spittal of Glenshee, passing through the beautiful scenery of Craighall, a few miles above Blairgowrie; but I would recommend those who wish to see Craighall in all its grandeur to put up in Blairgowrie for a few days and go through the walks, which is kindly permitted by the proprietor on certain days of the week. I have seen Airlie Castle (the " bonnie house o' Airlie" famed in song), and Hawthornden, near Roslin, but Craighall is decidedly finer than either. At Braemar, the tourist will be within easy reach of the home of our beloved Queen, and can find her sitting in the parish church of Crathie, amongst the humblest of her subjects. I would also mention Drummond Castle, near Crieff, the property of Lord Willoughby D'Eresby, with its magnificent gardens and noble trees. This is the finest place in the county of Perth, and the estate extends to between 30,000 and 40,000 acres. There are also many other places in Perthshire where the tourist can spend an agreeable day; but I will not further intrude upon your space, but conclude by recommending to your readers the Highlands of Perthshire as an elysinm for those desiring change of air and a " glorious quiet."

Epulov.

[26]

THE BOEHM FLUTE. Sir,—Will you permit me to correct an error which appears to have been made in the English Mf.chanic

of June 10th, wherein you gave a sketch of "Boehm" Flute. The flute represented isj "Equisonant," which your correspondent "Seile' describes in bis letter.

I should like at the same time to remove the impression which, it occurs to me, "Orion" intends to convey by his letter in the English Mechanic of June 17 —i.e., that the Clinton flut* is being abandoned in consequence of its inferiority to the other instruments he specifies.

In his attempt to do this he makes an unfortunate admission, as two extracts from his letter will show. He says, "I was induced to read Clinton's essay on his

Ante pereonaUy I know nothing of it." I fear

his reading benefits him little. As to his other assertion, I think he would have some difficulty in producing one instance of the Clinton tinte having been "abandoned" after it was once fairly adopted.

That within the last four or live years, the "Equisonant" has to some extent lost ground, I am not altogether prepared to deny; bnt this is mainly attributable to the death of its talented inventor, who died just M he had perfected his instrument, and might fairlv have expected to reap the benefit of the years of study, labour, and expense he had bestowed upon it.

Circumstances have since deprived the flute of that publicity, which in these times is so essential to success, and have given its opponents ample opportunity to deprecíalo its merits, which, nevertheless, are acknowledged by all who have given it an impartial trial, and which have alone enabled it to maintain its ground as well as it has up to the present time.

JrSTlTIA.

[27]

SQUARING THE CIRCLE.

Sir,—I quite agree with the remarks of Mr. H. W. Reveley, respecting the approximative^ correct solution of the squaring the circle by mechanical means ; bnt it is open to him to supply a superior method of hie own, on the principle of ocular demonstration, as he has thrown no new light npon the subject.

We live in a practical age and we are not up to ad infinitum,

Arthur Gearing.

[28]

THE BICYCLE.

Sir,—J. Hare (p. 309) thinks I was rather hard on the bicycle by (»Hing it dangerous, and informs me that he has performed journeys without a scratch. It was well for him that he had been so fortunate up till that time. That the bicycle with a few minor improvements will be the velocipede of the future, I by no means believe, but that t will have its day like longsleeved hats and chignons, and then become the bicycle of the past. If J. Hare, or some other practical bicycle rider, will give me information by answering a tVw questions, I in turn will give an account of experimental advantages and disadvantages of the three and four wheelers (the latter I believe to be the velocipede of the future). The questions are :— Does it require much practice and care to ride without falling on a smooth rood? On a bad road I have seen them twist about right and left like a stream of water running down a crooked brook; is that turning about to keep them from falling? If so, and you are in a narrow road, meeting a carriage or wagon, is there a danger of running into the carriage? or falling when turning a sharp corner {perhaps uphill) ? is not power over the machine lost, by the crank's being thrown out of proper position? and does the wheel rub the thigh? Is there a danger of thrusting the foot against or through the spokes? In treading the front wheel, sitting so far behind it, is it not like, and to be compared to, sitting in a low chair, placing the feet 18in. forward from the seat, then trying to rise up? Is there a danger, in jumping up when started, of pitching too far bock on the saddle and doing yourself a personal injury? Are the accounts to be relied on that we so often see in the papers, of ruptures, Ac., caused by riding the bicycle? How do you get it up a steep hill? would it make you dirty to lug it up if it was dirty weather? I took some luggage (10 years ago! on a four-wheeler 52 miles in 8 hours, I should like to know whether any one has done better with the bicycle.

N. G. Lamborne.

[29]

AN APPROXIMATE MODE OF RECTIFYING THE CIRCLE. gIR)—The following mode of approximately rectifying the circle may interest your subscribers.

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A corre»pümliii¿h- uear approach to the quadrature of the circle follows at once from this.

Richard A. Proctor. [30]

THE PHOTOSCOPE.

Sir,—I send you an illustration of the pretty optical recreative toy known as "The Photoscope," made in Paris, but which may be procured of Messrs. Cassell, the publishers of the "Popular Educator." It consists of a conical tube, of which the base corresponds with a screen or discV and is represented by ground glass, and the truncated apex of the cone is formed by the microscopical lenses and focussing arrangement. Fig. 1 shows the whole apparatus in elevation. A В is the conical tube, having the ground glass at the letter B, and the microscope slide-stage at A. In order to illuminate the object, the end of the instrument may be fnrnh-hed with a reflecting mirror like the Hollander's apparatns. A light tin conical tube, T, open at the bottom, is fitted over the eye-glass at E, when it is desired to project an image of the object in the slide on the ground glass at B. The instrument is either held in the sun's rays so that they impinge upon the attached mirror, or, if the photoscope is shown at night, a piece of magnesium band is ignited at M ; and whilst this brilliant light is obtained at M, the figure becomes visible at n if the lenses are carefully brought to focus by the lever at L.

In Fig. 2 the instrument is turned round so as to show the figure (not a гата avis) on the ground-glass ••creen at B. Of course, some practice is required in

[merged small][graphic][ocr errors][merged small]

The lenses used in this contrivance are shown in Fig. 3. The lens nearest the eye, or that to which the burning magnesium band is held, is a double convex, and is shown at A. The next is BB, the stage to carry the object, shown by the dotted line. С is a very small double-convex lens, of a short focus, which is moved towards A, or away from it, by the lever D. The diaphragm to reduce aberration is shown at E E, and being a very small aperture, it shows what great care must be taken to get the light exactly in the centre of the first lens, or condenser, at A. This optical arrangement is screwed on to the conical body, F F, which, as already stated, has a circular piece of ground glass fitted into the end I, (Fig. 1.)—В. T. K.

CALLAN'S BATTERY.

Sir,—I should have written on the above subject I.; ! week, but I considered the query a personal one, and knowing " Sigma" to be able to answer most of the questions addressed to him, did not wish to trouble you with two replies when one would be sufficient. Finding that he has not heard of Callan's battery under that name, I trust you will find space in your next publication for the annexed description of one which I possess.

Some five years ago I had occasion to vaponrizc thick metal wires for some experiments I then had in hand, and finding that I should require enormous power, I naturally looked about for the cheapest mode of producing it. Platinum I found out of the question, and I therefore tried the system of Dr. Callan, and had forty round cells made in cast iron, according to the sketch I send herewith, their dimensions being 7in. high

[graphic]

and 1 i u. diameter. Inside this cell I placed an ordinary porous one of large diameter with a rod of thoroughly amalgamated zinc in the centre. The outer cell was then filled with a mixture of equal parts strongest nitric and sulphuric acid, and the inner one with sulphuric acid and water in the proportion of one of the former to seven of the latter.

In order to ensure perfect metallic contact throughout, there were no binding screws throughout, but the wires were amalgated at either end, one being cast into the zinc rod, and the other dipping into a hole filled with mercury, which had been previously drilled in the projecting "lug" shown in the sketch of iron cell.

The reason of my making the upper part of greater thickness than the lower, is this: I found in practice that a great amount of wear took place at the surface of the liquid, and therefore by thickening that part the cell lasted much longer.

Now for the results—the battery being arranged for intensity, I used a copper wire ¿in. diameter, which was melted instantly with the production of a green cloud of smoke or vapour. Platinum wire of nearly l-16th in. diameter ran into drops, but was not vaporized, mercury gave off a perfect shower of sparks with a slight report, and also such a quantity of vapour that it partially salivated a friend.

In the end I think I may say that it is nearly as

Powerful as Grove's; but it has the following great effects. While the acid in the outer cell retains it« full power all goes well; but as soon as it becomes weakened, the action on the iron is so enormous that owing the ebullition the cell is in a few minutes almost emptied, while the fumes given off are something to be seen and felt before they can be appreciated. I would therefore not advise your correspondent to use it unless he make the cells double the height he requires, and then only half fill the outer one. Even then he will not have half the convenience of either Grove's or Bnnsen's.

T. S. Conisbek. Mg]

MANGANIC SESQUI-HYDRATE.—WATER
ANALYSIS.

Sir,—•■ Manganic Oxide's" query in your issue for the 1st inst. is not veri' definite, as the principal fact is omitted. On what quantities does he wish to act? A method that will suit perfectly for obtaining a couple of ounces, may be absurdly unsuitable for manufacturing a couple of tons, and rice vena.

Therefore I forward him four methods, each of which is meant for operating on a different amount, and to yield a resulting oxide of varions pnrities.

The first is only suitable for quantities not under In* pounds, and would succeed best with half a hundredweight. In an open, or a reverberator/ furnace, the oxide is to be roasted at a bright red heat, with small coal and coke, or charcoal and water, in the proportion of for every 100 pounds of oxide, 8 of small coal, and 5 of coke, or else 10 to 1 - of charcoal, and 25 of water. After the oxide is well reduced, a current of steam is to be driven over or through the mass until it is nearly cold, and the whole exposed to the air and kept well wet for some days. Treated in this way, the red manganic oxide yields about 70 per cent, of the manganic Yip. -.qui-hydrate.

The next two plans are only suitable for obtaining rough sesqui-hydrate, for laboratory use, and are not suitable for large quantities. The method is as follows :—

Place a mixture of i0 parts of manganic oxide, 2 of small coal, ¿ of nitrate of soda, and 5 of water, in a> crucible, and raise to a red heat as long as carbonic oxide is disengage. Let it cool, lixiviate with water, wash well, and boil with twice its weight of water, next add five times its weight of sulphuric acid of about specific gravity 1*5, and boil until nearly the whole is dissolved, let it cool, and precipitate with ammonia, wash well, and let it dry slowly. When only a couple or so of pounds is required, this is a very good method.

The next mode is only fit for obtaining a few ounces' at a time, and is the following :—A mixture of 10 parts of red oxide, Я parts of peroxide of manganese, t> parts of charcoal, and 1 of sodic carbonate, is to be raised to

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