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face of tbc stone upon which it is intended to oporate. The tool carrier k is connected by a joint to a lever n, actuated by the cum, the abrupt projections of which give an increased action to the hammer. This lever n is thrust away from the said cam by a spring o fixed to the carriage F in snch a manner that contact only takes place iu proportion as the spring is compressed by the pressure of the lever h. The action of this mechanism is rendered more sensitive by the combination of several spring levers all controlled by the same handle h. It will hence be perceived that the more the lever // is pressed down the more aotion the cam g has on the lever n, the ascent and descent of which is communicated exactly to the hammer, and in this case the latter acts on the stone to a correspondingly greater depth, the reverse of which will evidently take place if the lever A is moved iu the reverse direction. When this lever is raised it comes In contact with a lever p, the extremity of which works in a fork r, and acts against a screw s, which can be raised or lowered to any desired degree to limit the ascent of the said lever p. To this latter is joined a vertical rod carrying a ratchet or catch t, which gears into the grooves or teeth of the ratchet cylinder E. In this manner the greater the ascent of the lever j> the further the catch t will cause tho cylinder E to rotate, and the more the carriage I) will be displaced on the screw rod b.

"It now remains to explain the driving gear and the transmission of movement to the various parts of the machine. The pulley «, mounted on the vertical Hy-wheel shaft G, receives motion directly from the driving power ; this shaft communicates movement by the aid of a pair of bevel wheels to the horizontal shaft H, the end of which carries a grooved pulley round which parses a cord, passing also round a similar pulley on the shaft/, carrying the cam g, which actuates the double bevelled hammer or tool m, as above described. The workman directs the

tool carriage F by hand to anv point of the width or di'pth 'of the machine, whilst, by raising the handle h, he also determines at will the movement of the lower carriage D, and causes it to act successively by means of the ratchet cylinder E and screwed rods b, on every point lengthwise of the machine. Thus the attendant operative can not only move . the tool or hammer m instantly to any possible point of the millstone A. and cause it to attack the surface with any foroc or to any depth required, but he can also had the tool fixed upon one particular point as long as he thinks fit When the carriage D is at the end of its course it is taken back to the starting point by means of a crank r, which acts directly upon the ratchet cylinder E. The wheels then slide upon tho screw A, which remain fixed. To keep the driving-strap or band on 'he pulley H at its necessary tension, whatever may be the position of the carriage D on the frame B, an elastic cord or band must be used for that purpose. The sand or dust produced during the work on that part of the s^ono nuder operation is constantly expelled by a small bellows ■r, actuated by each upward movement of tho tool carrier *."

We have in this machine a horizontal rectilinear sliding movement, which causes the cracking to be done in straight lines, and a screw-feed motion at right angles thereto, by which those lines are made at regular distances apart. Any arrangement for securing the truth and level of th< stone is, however, wholly absent; the frame, resting on the stone, covers too small a surface, and the inner corner of it being over the oentral part of the stone, which is always somewhat depressed below the outer part, must bo held up by a special support, the adjustment of which would always be uncertain j otherwise the frame would rock on the two corners which rest on the outer part of the stone.

(To be continued.)

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30

SOLOMONS' NEW PATENT "COMPOUND SET."

IN 1868 Dr. AUnott wrote to the editor of the Times suggesting the great advantage that would accrue to meteorological observers from tho possession of a complete set of instruments. He, however, lamented that the cost of the complete sot—consisting of barometer, thermometer, hygrometer, rain gauge, anemometer, and zone cage, when constructed with tolerable accuracy, prevented the majority of observers from obtaining them. He suggested the construction of a combined set of all the required instruments (except of course the rain-gauge), mounted on a solid mahogany frame, which should exhibit at a glance all the existing physical elemental conditions. The Messrs. Solomons, of 30, Albemarlestreet, Piccadilly, speedily responded to Dr. Allnatt's suggestion by the construction of het compound set herewith illustrated, and which het Doctor in a second letter to the Timet characterised as " indeed amultum inparvo." The fet is indeed the best and cheapest we know of, its price, £2 12s. Gd., being so low as almost to inspire distrust. Its accuracy, however, is guaranteed by the testimonials of numerous purchasers

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who have hastened to avail themselves of an opportunity hitherto afforded by no other meteorological instrument maker.

The set consists of a barometer, with double vernier, maximum and minimum thermometer, Mason's hygrometer, thermometer with centigrade and Fahrenheit's scales, and storm-glass The tubes, enamelled, are of best, quality; the scales, of stout polished boxwood firmly screwed to a solid walnut, oak, or mahogany board, measuring 3ft. 3in. long, by 8in. wide.

Messrs. Solomons recommend the addition of their patent vernier thermometer, which, at the slight extra cost of 12s. 6d., renders the set complete.

The scales and two verniers of the barometer arc engine divided, and allowance is made for capacity and capillarity; so that it approximates in accuracy the nearest to the Kew standard. The storm or camphor glass, though much consulted by the late Admiral Fitzroy, is probably of little real use. Still it is attended with great interest, and being made by Messrs. Solomons exactly in accordance with the Admiral's receipo and with the glass tube of a larger size than usually sold is rendered, which prevents iu a great degree the attraction of the crystals to the sides, it is rendered as useful as possible. The hygrometer is a most important part of the set. Its aid to the physician is invaluable in the regulation of the degree of moisture or dryness necessary in the air breathed by his patients; to the householder who wishes to keep the air of his rooms in its proper condition; and to the horticulturist whom it enables to determine at will the climate of his conservatory. We think Messrs. Solomons fairly entitled to the credit of having, produced the best and cheapest set of meteorological instruments yet n traduced.

THE PROPOSED DARIEN CANAL.

THE Isthmus of Darien appears to be regarded by the majority of American scientific opinion as the most suitable Bite for the proposed inter-oceanio canal.

Dr. Cullen, an Englishman, claims to have made the most complete reconnoissance of the Isthmus of Darien. He claims to have fonnd a practicable route, with an elevation of not over 190 feet, and he thinks even less may be found. We submit bis map.

It will he seen from the map that he has a canal of 21 miles, and deepens the Sucnbti 12 miles, then navigates the deep streams, Lara,

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100 yards wide at I top and 26ft. deep. With its present imperfection they have taken nearly 100,000 dols. of tolls. The Dirien Canal, costing, say, 75,000,000 dols., would at least pay 10 per cent, profit, and Dr. Cullen estimates the actual saving to the commerce of the world in 1857 would have been 48,130,208 dols.-rnearly enough to have built it.

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Savana, and Tnyara, 14 miles more, in all 47, with one or two tidal locks—no other. He estimates this to cost about 34,000,000 dols., but his estimates are only for a canal 24ft. deep and 150ft. wide through the mountain or deep cattings. It wonld be folly to dig such a small canal at the present day. The harbours at each end will accommodate ships of the largest class now known, and at low tide the depth of water at the mouth of the Lara is 50ft. The tide rises there 12 to 14ft.

The canal, to meet the"requirements of modern

commerce of all characters, should, the Scientific

American thinks, be 50ft. deep its entire

distance, and 500ft. wide at top, throughout the

earth or valley cutting, and at least 150ft.

through the mountain section. Without the

most wasteful extravagance such a canal would

not cost near 100,000,000 dols. The actual

mountain section is not over three miles long, the

rock is soft dolomite, and coralline, limestone,

and gravel. Theclimato, unlike that ot Panama, is

comparatively healthy, and there need be no such

mortality as was witnessed in the construction of

the railroad. 10,000 Chinese labourers would in

rive years add another to the great works of

modern engineering skill.

The Suez Canal has cost over 80,000,000 dols., and it is estimated to cost 20,000,000 dols. mur ■ to make it what was originally intended—that is,

THE GERM THEORY OF DISEASE.

IN a letter to the Timet, Dr. Tyndall combats, as follows, some of the arguments against his germ theory of disease :—

Amid the morass of wordy discussion and contradictory argument in which the germ theory of disease and the question of spontaneous generation are entangled, the fart and inference broughtforward by Professor lister regarding the pntrefaotion of vounds appe;;sd to me to present a spot of perfectly firm gronad. They by no means involved the demonstration of the germ theory of disease iu all its generality, and \ thought that even those who are most hostile to the theory in its wider claims and bearings would be 'willing to concede that the origin of putrefaction, at least, was placed beyond dispute. Dr. Bastian's letter in the Times of last Wednesday causes me to fear that this admission on the part of those whom he represents is sti 1 distant, and that it was a delusion on my part to hope that it was near.

A similar delnsion may cleave to my judgment when I say that in a letter which fills nearly a whole column of the Time.<, Dr. Bastian has not, so far as I can see, brought forward anything beyond an opinion affecting, in one way or the other, the position of professor Lister. He deprecates "indireot evidence," uud speaks of the ambiguous experiments of Pasteur; he refers to the virtues of turnip infusions and to the killing of germs by heat; he expresses amazement, and protests against lixity; he exhorts, he warns, he promises results "which will go very far towards the settlement of the much-vexed question as to the possibility of spontaneous generation.'' But he successfully avoids offering the nhadow of an argument calculated to influence either affirmatively or negatively the distinct issue raised in my letter of Thursday week. Will Dr. Bastian forgive me for expressing the opinion that irrelevant writing has done, an! is likely to do, more damage to the cause of exact medicine than the distinct statement of even erroneous views? In the one case we have a definite error on which to place the iron heel of logic or of fact; in the other we are met by a phantom which eludes both. The question r.iised by my letter lies in a nutshell. Either Dr. Bastinn denies the iuability of lung filtered air to produce putrefaction, or he admits it; if the former, he can state his denial in three words; if the latter, I ask him to explain the fact.

Philosophical physicians have before now rendered immortal service to the cause of physical science; end, should the opportunity arise of making some small return for this service, it is mt the philosophical physician who will scorn our offered aid. The germ theory of disease, says Dr. Bastian, " appertains most to the biologist and the physician." Granted. But it is, nevertheless, true that the very best modem work connected with this subject has been executed, not by a biologist, not by a physioian, but by a chemist. This is not the opinion of chemists only. Some of the most eminent biologists of the present time speak with no uncertain voice of the demonstrative force of the experiments of Pasteur.

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I quite agree with Dr. Bastian that there is no proof that the organic matter of London air is all germinal matter. I do not believe it to be such. In fact, I have twice or thrice written down what the researches of others make the floating matter nf London air to be, bat tenderness for the public has withheld the description from the press. In the lecture, a report of which you did me the honour to publish, it is stated that "there is no respite from this contact with dirt, and the wonder is, not that we should from time to time suffer from its presence, bat that Bo small a portion of it would appear to be deadly to man." It is with reference to this "small portion" that I described the germ theory of disease. The really important point here is that the germs which are mixed up with the floating matter disappear when it disappears. Permit me to place in a connected form before the readers of the Timet the " indirect evidence" on which, to the surprise of Dr. Bastian, I rely. Schrceder and Pasteur have demonstrated that air filtered through cotton wool is deprived wholly or in part of its power to produce animalcnlar life. Why? Experiment with a beam of light answers the question; for while it proves our ordinary air to be charged with floating matter, the beam pronounces air which air which has been carefully filtered through cotton wool to be visibly pure. There are no germs afloat in it; hence its impotence as a generator of life.

Again, Pasteur prepared 21 flasks, each containing a decoction of.yeast, which he boiled, in order to destroy whatever germs it might contain. While the space above the liquid was filled with pure steam he sealed the necks of his flasks with a blow-pipe. He opened ten of them in the damp still caves of the Paris Observatory, ond 11 of them in the courtyard of the same establishment. Of the former only one showed signs of life subsequently. In nine out of the ten flasks no organisms of any kind were developed. In all the others organisms speedily appeared. Pasteur aseribed this unexpected result to the subsidence of the germs in the motionless air of the caves. Is his surmise correct?

The beam of light enables us to answer this question also. I have had a chamber constructed, the lower half of which is of wood, and the upper half of glass. On the 6th of February this ohamberwas closed, and every crevice that could admit dust or cause a disturbance of the air was cartfully stopped. The electric beam, when sent through the glass, showed the air at the outset to bo loaded with floatitg matter. The chamber was examined almost c"aily, and a gradual diminution of the floating natter was observed. At the end of a week; e chamber was optically empty. The floating matters, germs included had wholly subsided, and the air he'd nitiing in suspension. Here again the ocular demonstration furnished by the luminous beam goes hand in hand with the experimental result of Pasteur.

Next comes Professor Lister's observation regarding the filtering power of the lungs. Tinning once more to the luminous beam, we find that it declares air so filtered to be free from floating germs. Hence its inability to produce putrefaction, and the accompanying manifestation of nnimalcular life. Finally, as if to clinch the purely scientific experiments by a practical result, we find Professor Lister, actually employing citton wool to word off the atmospheric germs, and, by its agency, keeping a large class of wounds sweet and pure. It is this intimate welding together of two independent series of observations that Dr. Bastian calls indirect evidence j it is my reliance on such evidence that fills him with " amazement." In matters of science I always sacrifice the emotions, otherwise I might permit myself a little amazement too.

NEW LUBRICATING APPARATUS FOR MACHINERY.—For nearly two years an invention lias been practically tested on the Lancashire and Yorkshire Railway, from which a considerable saving in lubrlcstlng material is secured. The peculiarity of the Invention, which has been patented by Messrs. Bauer and Co., of Manchester, consists in the construction, in connection with the axle-box. of a chamber or receptacle lor oil, underneath the axle joucnal, in which a disc, supported on elastic or yielding bearings, Is partially Immersed. This disc, owing to the periphery of its upper surface being pressed against the axle journal, is made to rotate when the axle is iu motion, and a continuous supply of oil is thus transmitted to the journal and lis bearings, the amount being governed by a doctor or plate, provided with a slot that embraces the disc, placed above the level oi the oil. By.thls means a constant supply of the lubricant being insured, the possibility of the bearing* getting hot, which often happens when the salve lubrl cant is employed. Is prevented.

LETTEES TO THE EDITOR.

[We do not hold ourselves responsible for the opinions of oar correspondents. Tbe Editor respectfully request* that all communication »hould be drawn op as briefly as possible.]

*.' All communications should be addressed to the Editor of the English Mechanic, 81, Tavistockstreet, Coveoi Garden, W.C.

All cheques and Pott Office Orders to be made payable to J. Pasbmobe Edwards.

T would have every one write what he knows, and as much as he knows, but no more; and that not In this only, but in all other subject*: For snob a perron may have some particular knowledge and experience of the nature of such a person or such a fountain, that, aa to other things, knows no more than what everybody does, and yet to keep a clutter with this little pittance of his, will undertake to write the whole body of physicks: a vice from whence groat inconveniences derive their original. — Mon/aiaiie'i Ernaf/s.

THE TELESCOPE.

Sib,—"Amateur" (24.">li is confusing angular and linear magnitude, in a way nothing short of marvellous. In its existing form his"question admits of no answer; but the following considerations may posaibly tend to help him out of bis difficulty. The disc of the Snn subtends an angle oi about of, and 112'(as "Amateur " may discover by reference to a table of Natural Sines in the first set of mathematical tables he can lay his hands on), or the sine of 32', which practically coincides with the arc, is 0093 of the radius of the circle on which it is measured, be that of what size it may. Now in most books on Optics, lOin. is taken on the standard distance of distinct vision; multiplying, then, O093 by 10- we get •tryfiiu. as the length of aline subtending an angle of 32' at ICin. from the eye. In other words, if yonr correspondent will cut out a little disc of card, wtin. or roughly liu. in diameter, and Interpose it between his eye and (he Sun at a distance of loin, from the firmer, he will find that it will just hide the Suu from his view. If. then, we multiply, -093 by 40- we shall get. 3'7Jin.; or by 00, 0 oSin. as the apparent diameter of the Sun with the powers he specifies. This is however only true at Vie one specific distance oj Win. from the ene; since, for example, the S72in. image would appa rcntly coincide with one of 10 321n, or the 5 58ln. one with another of lUsin. if the latter were removed to a distance of 5ft ; and, Ho faros "Amateur's "<]oery, In any shape, admits of a response at all, this must be my reply to it.

"a Ursa! Minoris " (24*7), same page, is very much less difficult to answer, inasmuch as "a partially silvered speculum,'' and" a single plano-convex lens for an eyepiece " supply all the conditions needful tor the production of any amount of fog, glare, or indistnctness. "a Ursa;" omits to say whether tie ploBe or the convex surface of the single eye lens Is turned towards the mirror; but under any circumstances, bis friend ought to get some good Huyghenlan eyepieces forthwith, always supposing that nla speculum is worth them, and have that properly slivered into the bargain.

1 may inform Mr. Bagulcy (249S), p. 95, that any optician whatever, would make him a Ramsdeu's eyepiece. Slater, of 138, Kuston-rood, Loudon, would be a very good man to go to, were he a little less dilatory; or Maker, of 543, Hl^h Holborn or Murrcll, of 5a, Mitchell-street, St. Luke's, both In London, might be depended on. From 12s. to las. would be a fair price to pay for it. Two ways only occur to me in which Mr. B. could deepen the colour of his sun shade. The one Is to have a piece of green glass cemented oa to his present red one; the ether is to Bmoke its internal surface over a candle. The latter is the more feasible, as the first would render the eyecap Inconveniently thick. It is Impossible to re-colour the glass, but Baker would take it out and replace It with another of any tint your correspondent chose for about a shilling.

A Fellow or The Eotal Astronomical Society.

ASTRONOMICAL.

Sin,—"Gimcl" (2448), p. 94, speaks as though Le Verrler had both computed the mass and distance of Neptune, and made the optical discovery of it as well in his own person; at least so I interpret the words "by calculation and observation," which he employs in connection with the name of the great French geometer. Le Verrier computed the hitherto unknown

Slanet's place in the Heavens, as did Adams too; ut the former communicated the result of his calculations as soon as he obtained them, to Dr. Guile, of Berlin, and he, searching In the indicated region, at once found Neptune ; so that Dr. G. was what would be vulgarly called the discoverer of the new planet. "Glmel" may get some idea of Adams's process from Vol. 16 of the " Memoirs of the Royal Astronomical Society," and from the" Supplemeat to the Nautical Almanac for 1851."

Did it never oecnr to "H. A. C." (24J52), p. 04, that the very circumstance of bis pseudo Satellite of Venus disappearing with a change of eyepiece was, in itself, a very suspicions one? The probability is, that had ho only turued the 240 eyepiece round In the tnbe, while watching the planet, he would have Been his

supposi tfttous moon describe a complete orbit about its primary, and so have convinced btmself that it had its origin and existence within the eyepiece itself, and nowhere else. A Fellow or The Rotal Astronomical Society.

DARK LINES IN .*OLAR SPECTRUM.

Sir.—" T. A." should state his evidence. All 1 con at present say Is that his view is opposed to ail the evidence I know of. T'* ere are certain characteristics we should exjicct to find In dark lines, caused by our own atmosphere; certain others we should expert to find in dark lines reallv belonging to the sobir spectrum. We find accordingly that the dork liues may be divided Into two classes-ibc atmospheric and the solar. Has "T. A." any reason to show why the latter dark lines 'ail or any of them) should bo plnced in the somo category with the former 7

It. A. PnotTOR.

JUMPING FROM A TRAIN IN MOTION.

Sir,—A friendly correspondent points ont what he holds to be a mistake in my remarks on this subject. Ou looking at my letter, 1 find the.ro is room for misconception. I was not referring to the ease of one who wlshe< 'evil-disposed man !> ;o leave a carriage "while the train is still In motion," against the laws made and provided by the authorities, but to one who wished to leap from a rapidly moving train. Whenever it Is possible. It In always well (as every one knows) to move in the same direction on terra firma as in the train. Even then, however, the motion with which one leaves the train is only forward with respect to terra firmat not with respect to the train; but where one has to spring from a train iu rapid motion, and fs quite sure of a fall, one may escape broken limbs by leaping strongly in a direction contrary to that in which the train is moving. Unfortunately, one cannot very easily do this. It is, however, useful to learn that when one is in an open carriage and the horses run away, one may effect an almost certain escape by springing sharply from the buck of the carriage (supposing its construction suitable). I do not speak without having tried the experiment—not, indeed, in the case of a runaway trap, but from the back of a truck moving with considerable swlftuest.

Oae can easily establish the general principle on which the matter depends. If any one will amuse himself by throwing stones from the back of a carriage, he will find that after a little practice he cun so throw a stone in that direction, thfit the stone will fall dead still on the spot where it first touches the ground.

I see by your " Replies to Correspondents" that you think Mr.'Iieardsley should be answered.' With all respect. I confess 1 am of another opinion. I think no student of science who values his reputation could seriously enter into discussion over such puerilities as those with which Mr. Beardsley has tilled nearly a column of your space.

It is one thing to exhibit the evidence on which the earth's figure, Ac, depends, and quite another to take up the challenge which " charlatans and enthusiasts" are ever ready to throw down. Snrely your readers must all sec for themselves that Mr Reardsley's letter needs no answer. If we spring from the lloor of a railway carriage, we are not forthwith flung against the rear seats. A passenger on a rear seat would not find it more difficult to throw a ball to a passenger on a front seat than the latter would find it to return the compliment; yet for Mr. lleardsley's argument these and all the thousand evidences derived from daily experience must be forgotten. The real fact is, that it. is not with tlio teachings of astronomy he contends, but with the familiar principle known as the second law of motion. It would be absurd to reason with him.

If he were to point out any flaw in the reasonings in my paper on the earth, 1 should feel bound to set matters straight; but as a matter of fact, he has gone out of his way to deal with tilings I have not touched on in my paper, conceiving as I did that to explain such matters to those for whom the English MechaNic is primarily Intended would be to carry coals to Newcastle. If- A. I'boctor.

EKGLISHMECHAXICMUTUAL IMPROVEMENT SOCIETIES.

Sir,—The letter ia last Issue but one, on English Mechanic Mutual Improvement Societies has given, no doubt, great satisfaction to many subscribers of our paper besides myself. The same thought which has been so vividly depicted was also in my mind, but true, iu a dormant state, wal ting, like the worm for the spring, to emerge from its cover. Will you therefore allow me to take a part in the movement, and propose to the subscribers living In Manchester to assemble one night this week, to discuss rue subject— namely, the formation of a Manchestrlan English Mechanic Mutual Improvement Society, I feel convinced that much benefit would be derived from such a society, and would In some measure be a reward to our indefatigable editor, in effecting prosaically the truth In the editorial article, "Ourselves and Our Subscribers."

Having been fortunate enough to make arrangements with the landlord of the Dog and Partridge Hotel, I suggest that we meet there on Friday evening, 29th April, at 7 o'clock, when I hope to meet many subscribers. A. Tolhauben, Manchester.

WORKMEN'S INTERNATIONAL EXHIBITION,

1870.

Sir,—As the interest in tho Workmen's International Exhibition is dally increasing, a few words upon the subject may be acceptable, and perhaps useful, to many of your readers. The following despatch, whlcb has been received by the council through the Foreign Office, will give an Idea of how warmly the subject has been taken up upon the Continent:—

"The council of this exhibition have received the

foltowtn; despatch through the Foreign Office from Signer Yiscouti Vonosta, ono of the Italian Ministers : — "Florence. February 26lh, 1870.

'Sir,—His Majesty's Government took care to give the greatest possible publicity to the notices contained In your notes of the 20th June, 8th of October, and '.".iiid of December, isiW, relative to the Workmen's International Exhibition, which Is to be opened iu London next Jim?.

• I am glad to isforra you that the Idea of that exhibition has been most favourably reeefve/i in Italy, and that in the most important cities o! the kingdom no delay has taken place in constituting local comuiiuces which have spontaneously assume* the duty ot encouraging It.

'The King's Government, on Its part, has in a special manner requested the Consultative Commluee on Provident Institutions and Labour to prepare and solicit the participation of our country in that exhibition, and its Executive Committee has just published a code of regulations, copy of which is enclosed, explaining the course to be followed by Italian exhibitors.

'Yon will perceive that independently of the subsidies which may be voted by the provinces, communes, and Chamber of Commerce, or accorded by private individuals, the exhibitors are entitled to gratuitous transport by sea of the articles for exhlbiiion, aud to the reductions usually grouted in similar cases by the railway companies.

'1 must add that the King's Government intent! instituting an Italian commission in Loudon, which will provide for the reception and placing of the articles and for their reconveyance to Italy.

'I am convinced that this commission will receive the support of the British authorities charged with the direction and regulation of the exhibition, and in this conviction I avail myself, &c.

"(Signed) Visconti Venosta."

The following reprint from the Daily Ai-ip-j will give a good idea cf the intentions of this exhibition :—

"It is Intended, as no doubt most of our readers are aware, to hold a Workmen's International Exhibition iu LondoD, In Jnly, 1870. The distinguishing features of the scheme nre>—

"1. All articles exhibited will be signed with the name of tho workman by whom they are made. "2. In those manufactures in which division of labour prevails, workmen will be Invited to exhibit specimens of that particular branch of work in which they nre severally engaged. Thus, for-instance, a watch or a piano might be exhibited, showing in a complete series the various parts on which workmen are severall v employed,ond the various steps by which it approaches completion. Each workman will thus have the opportunity of showing his skill in his own special depigment, or of (calling attention to any improvement in the manner of manufacture he may wish to introduce, and the public will better understand the whole process of construction through which the completed article bos passed. 3. Workmen are invited to combine lor the production of the same article. Iu all' rases the article will bear the workman's signature.

4. To show the various processes of manufacture, and to arrange these in such a manner that the English and the foreign process may be compared with each other, and lectures given In explanation of the relative advantages possessed by the different methods.

5. In the same way, for the purpose of comparison, when the manufacturing process is of such a character that it cannot be seen In operation, an endeavour will lie made to show, side byjsldc, by means of drawings and models, some important variations in themcibodis pursued in different countries.

"The Right lion. W. E. Gladstone, M.P.. is tbe president, supported by noblemen and gentlemen of all parties as vice-presidents; the executive committee consists both of men of position and artisans, assisted by a handsome guarantee fund and good list of subscriptions. An agreement bos been made with the Agricultural Hall Company for tbe use of their hall at Islington, la which there is ample room for exhibits, aud which will contain 30,000 visitors. Very considerable progress has been made not only in this country, but in foreign countries. Side by side with the contributions of our own country will be the productions of the French artisan, of the thoughtful German, of the artistic Italian, of the persevering Dane, and of our American cousins.

"Local committees have been formed at Venice, Verona, Florence, Turin, and Genoa. The Syndic of Palermo has announced that the artisans of that city shall have their contributions forwarded to London at tbe expanse of the commune. In the Italian cities subscriptions have been raised to pay the expenses oi transit, &c. The exhibition has the hearty support of General Garibaldi. Tho secretary of the local committee at Florence was the general's intimate friend aud companion, Signor Dolfi, who continued his efforts until his lamented death. He has been succeeded by Signor Dassl. the president of many workmen's institutions. Throurh the hearty exertions of the Right Hon. A. II. Layard, the chairman of the committee at Venice, and Hon. Secretary Dr. Errara, twenty picked Italian artisans will be sent to London to visit the exhibition, aud the committee In London will endeavour to extend their visit to Manchester, Leeds, Birmingham, and the other great centres of manufactures iu this country. In Germany committees are being formed at Berlin. Frankfort-on-tbe-Maioe, Mayence, Dnnnstadt, Offenbach, Stutgard, Carl'aruhe, and Munich, at Pesth in Hungary, and at Warsaw in Poland. Tho Baden contributions will be collected at Caiisruhe, and there exhibited, andjtben forwarded to London at the expense of the State. The Wurtemburg Government has voted 10,000 florins for the nsc ot tbe committee at Stutgard, for the expense of transit and to give subscriptions to workmen desirous of visiting the exhibition. Committees are also formed at Copenhagen, Hamburg, Rouen, and Brussels. A very active and energetic committee is formed nt New Orleans, and contributions are promised, and the manufacture of sugar will be exhibited, as the makers of this article claim to have reached a great degreo of perfectiou. The South Carolina Sute Agricultural and Mechanical Society have placed themselves at the head of the movement in tbe Southern States of America. The Earl of Clarendon, her Majesty's Secretary of State for Foreign Affairs, addressed a circular letter to all her Majesty's ministers, envoys, nnd consuls abroad, requesting them to Rive publicity to the exhibition, and to promote the formation of committees, and to assist with all their influence the objects of the council of the exhibition. The principal effect of this circular has been toconvinee the council tbatmany places would have been entirely excluded unless agricultural produce and raw material used lu manufactures were admitted. The council, therefore, have decided not to oxclude those articles, and through the energetic help of our «ou*ul», agricultural produce, Ac, will be exhibited from Patros (Greece), Algiers, Maples, Cagllari (Sardinia', Kew Orleans, Liibon, San Francisco, Corfu, Madeira, Galveston (Texas), Klo de Janeiro, Mobile, Lima (Peru), San Jose, Oosta Kir:i. Norway, Havana, Pars, Rosario. Bogota, and Monte Video. To meet the views of tho Russian Government the council will endeavour to make arrangements so that the articles exhibited In tt Workmen's Exhibition at St. Petersburg in May next rnny have place in ;the London Exhibition. The council also have been In communication with the French Government, and they have every reason to hope that an admirable display of French workmanship will be exhibited. The Duke of Argyll, her Majesty's Secretary of State for India, has announced that a selection representing Indian art manufactures shall be exhibited, and the expense of fitting shall be defrayed by the department.

"To meet these very energetic efforts made In foreign countries, seventy local committees have been formed in the United Kingdom. As an example, the city of Belfast has a very active rommittoe, of which Mr. \V*. Kirkpatrick (of the Aorthrrn Whig office) is the able -and efficient secretary. Avery ample subscription has been raised to meet tlie current expenses, and to pay part, or the whole, if possible, of the carriage of articles to London. The committee has also received the countenance and support of the lending manufacturers, who have promised to give every facility to w jrkmen in their employment who may express a desire to produce articles for the exhibition. It is hoped that the artisans of this country will make a most determined effort, so that the Workmen's International Exhibition of 1870 will not only be a display of the best foreign workmanship, but an exposition of the talent, industry, and manipulative skill of the British workman

"To further tho objects of this exhibition, the King of Wurtemburg has directed that his name be added to the list of guarantors for the amount of £100. The President ot the Republic of Peru has directed that all the expenses of transit of articles to the exhibition, with the expenses of the Central Committee at Lima, such as printing, postage duties, &c, shall be defrayed by the Stato. A handsome subscription has been forwarded to the hon. secretaries of the exhibition by the British residents at Buenos Ayres."

It has nlso been proposed to open workshops in the exhibition building, and to give prizes for the highest skill shown in tho use of various tools.

In the scholarships, Bo generously given by Mr. Whltworth for mechanical science and practice, about an equal amount of marks are to be given for theoretical knowledge and for manual skill.

The examination for these scholarships, which Is to test the manual proficiency of the candidate, consists of two parts. In tbeflrstpartthecandldate isrequired to produce certificates, to exhibit work special!/ executod for the occasion, Ac. ; in the second part be is required to show a knowledge of various tools, by the performance of one or more of the following pieces of work:—

The Axe. a. To square up a block of wood 1ft. long and 6in. in diameter, o. To make s spoke for a cart wheel, c. To shaft an axe. «!. To cutout wheel spokes ready for fitting into nave.

The. .lair and riane. a. To saw from a plank two pieces of timber 3ft. long and sin. square and plane them up true.

o. To make a box 18' long x V wide x 9" deep planed up true and the Joints dove-tailed together. .,£\ To »aw out and plane up two parallel strips 2' d* x 2" 2" x I'.

The IJammer and ChUel. a. To chip apiece of cast-iron Gin. square over on one of its surfaces ready for filing.

». To cut out'of sheet iron (any gauge) a figure or 11 tter of any size from 1'to 6'. The file, a. To file two sides of a cast-iron inch cube as flat as possible with a Stubba' 13ln. second cut file, the stroke of the file not being less than Sin.

A. A wrought iron hexagonal nut J' or 1' to be filed op true. e. To file up two parallel strips, iron or steel. o. To file up pocket square as true as possible. The Foryt.

« To weld or join together two piece* of iron Jin. square.

*. Te make a pair of smith's tongs.

e. To make the head of a hammer.

n. To nuke a pick.

e. To make 2ft. jln. chain with hook and ring.

f- To make a horsc-sboe complete.

g. To cutoff and draw out chipping chisel or drill, and afterwards harden.

*' J" nu.ke * P»ir °' "maJI callipers. «. To make a pocket square.

It is with this part of the examination that we are nero concerned We are Impressed with the soundness of judgment which has led Mr. Whitworth to give weight to msnuol as well as to theoretical proficiency Hi the examination, and It seems to us that the forthcoming exhibition would offer to workmen of different countries an interesting opportunity of competing in the skilful use of the most important tools.

Besides the tasks of work required from candidates Tor Mr. Whltworth's scholarships, many others maybe suggested, such as :-Joining—The putting together a TM2JJ\ Turnery—To turn in ivory seveu balls, one within the other, the outer one not to be more than I,'

In diameter. Engraving—To engrave on glass and stone nnd metal; the engraver working' from a copy or Inventing the design, which would tie required to suit certain circumstances, to be made known at the time. Modelling—In wax, clay, leather, Ac, tlie designs to be original and from copies. Carving—In wood and stone. Inlaying—Jn metal, wood, and stone. Designing—Of articles belonging to the textile trades, the glass trade, the porcelain trade: tlie designs to be original, and to snlt special circumstances to be made known at the time.

The rules to be observed by exhibitors are as follows: —

1. Tbe exhibition to be opened on tlie 7th July, 1870, at the Agricultural Hall, Islington, London.

2. No charge will be made for space.

.1. Space will be allotted to exhibitors by the council of the exhibition.

4. AH articles must be brought, exhibited, and removed at the risk and expense of the exhibitors.

5. All packages arriving at the exhibition In the absence of the exhibitors or their agents, will be opened by tbe servants of the council with the greatest care, but at the risk ot the exhibitors.

6. Articles once exhibited must not be removed during the continuance of the exhibition, except by permission of the council.

7. All property not removed within seven days after the close of tbe exhibition will be dealt with as the council may direct

8. Exhibitors may appoint persons, subject to the council's approval, to take care of articles exhibited by them, or to explain them to visitors.

9. The council will supply counter, wall, and floor space, but any special fittings must be furnished at the exhibitor's expense.

10. In cases where a number of workmen combine to produce any object, the name of each workman must be given, and tho portion executed by each specified. The same rule will apply to all articles exhibited by manufacturers and employers, which will be admitted subject to this regulation.

11. All articles intended for exhibition must be approved by the council, or such officers as they may appoint, the council reserving to themselves the right of rejecting any articles which may be unsuitable.

12. All articles must be delivered at the Agricultural Hall, Islington, between the 20th of May and the 25th of June, 1870.

The Board of Trade are preparing a bill for the protection of Inventions shown at the exhibition, so that inventors need entertain no fear of their inventions being pirated without their being able to help themselves, as the mere fact of the invention being ex* hibtted in this exhibition will bo a provisional patent in itself without further expense or trouble of any kind whatever.

The space allotted to English exhibits Is belm; rapidly taken up, and the last day for receiving applications Is April 25th, so that Intending exhibitors will do well to make early application to the hon. secretaries of the Workmen's International Exhibition, 150, Strand, betweon 10 and 4. Every Information, space forms, Ac, can also be had on personal application to the St. Mark's Club, 11, Brown-street, Duke-street, W., London, between 7 and 10 p.m.; or by letter enclosing stamped itirected envelope to

Kobebt IitnuESg, Local Secretary, 22, George-street, Oxford-street, W., London.

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VELOCIPEDES.

Sir,—The many erroneous notions that prevail among inventors In regard to this form of locomotion will ever prevent its general adoption, the foremost of which is, that speed cannot be obtained without great expenditure of the moving power, an axiom true in regard to stationary mechanics, but one that has no place with locomotive vehicles.

The great obstacle of rough roads is best overcome by excessive speeds, not by slow motion and main force, especially as muscular strength will enduro for a far longer period with slow than rapid motion

In all the velocipedes and bicycles now in use the only gain in speed ovor an ordinary walking pace is the difference between the eirenmfereuce of the driving wheel and the walking tread, so that in order to gain a speed of more than 7or 8 miles an hour as impossible rapidity of muscular action it required, and until from 15 to S*n miles and upwards be possible, velocipede riding will never become generally a mode of locwmotion. Fortunately, we are now* in possession of a means of obtaining any rate of speed, limited only by the resistance of the atmosphere al high velocities, with slow muscular action. By the use of indiarubber tires all carriages are rendered independent of bad roads. The tires moat not, however, be in the form of thin plates, as proposed by the " Phantom" Wheel Company, but most have a depth of between two or three inches In order to be effectual. Also in multiplying the motion of the treadles by a wheel and pinion in the proportion of four or six to one, stout india-rubber tires to both wheel and pinion will prevent all clatter and friction, when with 4ft. driving wheels, loose on their axles, 30 miles maybe readily attained, while tbe muscular motion of tho drivers1 logs will only be equal to that of walking at the rate of two or three miles in the same period. The universal up and down vertical tread is also a great mistake, for it can only be compared to running up the Monument stairs with half-a-hundred on one's back; whereas, if the strength of tbe legs be used in the horizontal position it is found to be equal to a one-normpower. For a strong man, such as Topham of the last century, and many others, have successfully withstood the pull of a brewer's droy horse. Some inventors put forward the absurd idea that the weight alone of the driver should actuate tho propulsion. Others again would use both legs and arms; in fact all tbe muscles of the body at tbe same time, rapidly producing an cxbausMon that no human frame could endure for many minutes.

It is scarcely necessary to allude to the trotting velocipede, or that most glaring absurdity of propulsion by menus of a spiral spring, patented by M. Ferdinand Constant Colney, of Paris, who makes the additional blunder of after having obtained circular motion, introducing the crank system. His spiral spring would require a considerably greater power to wind it up than would be required to propel the carriage direct. A light carriage for 3u miles an hour with slow treadle movement is figured and described in a former number of the English MeChanic, under the title of tbe " Velocifere."

Henry W. Reveley, Heading.

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SLATER'S ELECTRO-MAGNETIC MACHINES.

Sir,—A description of Mr. Slater's newly-patented electro-magnetic machine may probably Interest your readers, so 1 send an abstract ot tbe specification. The said invention relates more particularly to various improvement* in the construction of electro-magnetic machines as motors, and in the construction and mode of exciting batteries, and in the application of such motors and batteries to various useful purposes. These improvements consist, firstly* in the construction and arrangement of electro-magnetic machine*, and ;in : transmitting the force obtained through these improved batteries and magnets, and rendering such force available for useful purposes either through a reciprocating or rotative movement. Mr. Slater constructs his magnet of the form shown in Figs. 1 or 2; Fig. 1 is of the horse-shoe form, circular in section, but swelled out at the poles of the magnet at tbe end of each limb, so aa to give a greater surface for tbe armature to work on, and otherwise for the Increasing of the surface of the armature and power of the magnet. A. A1, Is the magnet, either made of solid wrought iron and circular in section, or aa in Fijf. 'Z built of sections of flat soft wrought-lron plates, but also swelled out at the poles of the magnet Eliher one magnet is used, as in Fig. 3, or more than one (iua series, as in Fig. 4, Increasing substance so as to obtain a greater attractive force for tho armature to be attracted against by the " moment of force" alternately. 11 is the armature of a compound form built up of a series of wrought-iron plates, ns shown in section, Figs. 1, 3, 4, 6. Tbe outer edge of the arma

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tare works on the outer edge of the poles, or nearly Bo, of the magnet, and not absolutely in contact when raised from the poles, a* shown at C, Fig*. 3, 4, and ■'•; each end of the armature having journals D to work on, to keep it always fn its proper position, so that the heel of the armature may be nearly Into contact at all times with the poles when raised from the magnet. Attached to each of the armatures are levers E and E1, to communicate the electro-galvanic force from the armature to the connecting rods F.F1, thence to the cranks G, G1. which are attached to the running shaft II, on to which is affixed fly wheels I, so as to maintain the momentum of the machine. There is an Arrangement on the main slinft or on a separate shaft driven by the former, on which is placed "commutators "of metal J.J1, which revolve with theBhaft, and on which the conducting wires K, K1, form the battery work, or In other words are in contact; but on these revolving discs or commutators arc inserted pieces of ivory or any non-conductor, so that as the "commutators" or " discs" revolve the force from the battery is laid on to the magnet when the armature is raised to the angle required, and when attracted downwards the wire passes on to the non-conducting surface and releases the armature, when it is raised to the position C again, and so on in succession for any number of strokes per minute. By this repeated layiug on and taking oft the force, the armature B rocks up and down, the faces of the armature coming into contact alternately with the faces or poles of the magnet, producing the reciprocating movement as described. The power of the machine is increased in a ratio not yet ascertained in practice by the introduction of the compound armature, but it has been found to be so material that the Bolfd iron armature has teen abandoued in consequence. In transmitting motion to the crank shaft from the armature B through the lever E and connecting rods F and F1, it will be readily Been that the crunk is in its worst position for the transmission of dynamic force to the rotative shaft at the time when the armature is receiving in greatest attractive force from the magnet, but in order to obviate this difficulty the connecting rods are made of Hu elastic material, either of caoutchouc, or of helical sprin^Bof steel wire, as shown in Fig. 7, but supported with extending sleeves In the inside in sections like a telescope slide, so that when the armature closes on the magnet and the force is disconnected, the connecting rod will assnme its normal length agniu before passing, or at the time of passlag the lower centre of sua anj?le of !H)°. 'J he branches of the magnet are coiled 1.-it nud right with its equivalent of insulated copper wire, »o that each end of the horBe-shoe may have its opposite polarity, the ends of these wireB L, L1 are attached with the negative and positive poles of the improved battery. Electro-magnetic force in electro-magnets of this kind Is due to the induction current, which the development and disappearance of the magnetism of an iron core indicated by the insulated spiral surrounding it, which la termed excited magnetism. Much depends also on the area ol the nection aod facea of the two ends of the limbs of the horse-shoe, which are the poles. In his improved magnet Mr. Slater swells out the end of such limb of the magnet at the poles, as shown in Vlgs. 1,2, 3, 4 and

6, so as to increase the surface of the poles, and also allow more attractive force and surface frr the armature to work against lie alto constructs a rdngle machine, as shown in Fig. 8, where a, a, is the frame or support of the machine, A the magnet, B the armature, and-lever E, the connecting rod F, and the fly wheel I. The commutator, or disc, for laying on and off the fluid from the battery, may be placed on any convenient part of the machine.

Another form of working a double compound armature is shown in Fig. 5, where the magnets A. A, are placed horizontal, or nearly so, and the armature B works between them, and the leverage for the connecting rod d to transmit the power is taken off at the point e, so that the armature would rock on the bearing or Journal 0.

In regulating the action and velocity of such machines to suit various loads, a governor of very simple construction 1b used, by placing a small plunger " cataract" governor between the battery and the magnet or magnets, Buch machine to have a valve at the bottom as the plunger ascends to let in fluid from the small cistern, the regulator being a valve or tap to let the water out slow or fast, as the case may require. Tin-, will act on a small mercury bath in which the conducting wire is Immersed, the immersion being regulated by the governor as before described, which regulates the speed in proportion to the load on the machine at the time.

In his Improved battery, and also improvements in the manner of using such batteries with one or more cells, as shown in section Fig. 8, Sir. Slater uses excitants differcntttrom those commonly used, especially when a uniform current is required. As the Bunsen battery is of similar construction, it will be necessary here to explain the difference between his improved battery and that of the former. Instead of using zincs in the outer cells and carbon In the inner cells, he uses soft Iron plates or cylinders in the outer cells in combination with his improved method of exciting such metals as described. At the name time he uses the carbon in the inner cells, but with a difference also in his exciting solution as described. The excitant lie prefers is u saturated solution of nitrate of soda or ultrnte of potash. The former is found best and cheapest. In this solution the plates of Iron (if a battery of flat plates), or cylinder of iron (If for cylindrical cells) are placed in the outer solution, as in section Fig. 8. Then the carbon or graphite # is placed within the porous cell A, which cell contains nitrous acid of the specific gravity of 1*60, or any weaker fluid containing In solution nitrous or nitric acid; but the stronger acid is preferable. The acid iu theporous cells h should be about lin higher than the solution iu the outer cells in which the iron cylinders are placed. The infiltration, or exos, or endosiuosis process through the porous tubes or cells h keeps the outer solution coutatnintr nitrate of soda constantly supplied with acid, preventing it from becoming alkaline. When the iron and carbon arc properly excited iu their cells, the constant action of the battery can be maintained by adding about one-sixth to one-third of fresh nitric or nitrous acid daily. This partly exhausted ucid solution Is mixed with the nitrate of soda and used for exciting the iron In the outer cells,

adding'a small quantity daily in accordance with the amount of work done.

Another method of compounding a useful excitant is> by usiDg nitrous and muriatic acids, the former of tm» specific gravity of 100, and the latter about 1-200, in equal proportions (by measure) to be used in the carbon cells, and the nitrate of soda as before described in the outer cells. Or a very powerful current is generated when nitric or nitrous acids are used alone or combined with sulphuric or muriatic acids In small proportiouB in the cells with the carbon, and dilute nitric acid is used in the outer cell with the Iron. When the nitrate salts are not used, nitric acid Is used in tht outer cells. The filtration through the porous cells will keep the outer excitants for the iron nearly uniform iu strength until the iron solution Is almost of a pasty consistency. Where great Intensity is required iu batteries, especially for telegraphic purposes, the saturated solution of nitrate of soda or potash only is used both Inside and outside of tbe porous cells. Furthermore, if an Increase of power is required without adding to the number of cells In the process of working in any eBpecial c,ase, then to tbe nitrate of soda solution In the porous cells is addei about one-tenth part of weak acetic acid nr common vinegar. D. F. K.

COMBINED PUNCHING, SHEARING, UPSETTING, AND STRETCHING MACHINE.

Sin,—I send you drawings of a very Ingenious and useful little machine of American origin, which has been lately introduced into this country by Messrs. Towle and Harding, of i'8, Newgate-street This machine, which is constructed by Messrs. Reed and Bowcn, of Boston, U.S., is intended for shearing, punching, bending, and shrinking or stretching tires or hoops, and when constructed In the form we illustrate is adapted for being worked by hand power. The machine, in fact, although capable, when worked by one man, of cutting easily bar iron 2£in. by -£in. or 4in. by gin., weighs only ;i."iOlb.

Referring to Fig.l,|lt will be Been that the main frame A of the machine, consisting of the two sides and the tep and bottom is cast in one piece, the cam B being placed between the two sides and hung on the pin C. The first lever D works into this cam. ahd la hung on the pin E, the knife F, for shearing, being attached to this lever and the knife V1 to the main frame A, The second lever G Is connected to the first lever D by the straps H, and to the main frame A by the straps H ■'. The third or band lever I Is connected to the lever G by the straps J, and also] to the main frame A by tbe bolt K. This forms a very powerful arrangement of levers, giving with ?001b. on the hand lever a pressure of over 52,0001b. on the shears and 72,000lb. on thepunch. The straps II, II-, and J ore in pairs, one on each Bide of tbe machine.

The operation of shearing is performed by placing the metal to be cut between the knives F and K-, and then bearing down on the hand lever I. The tire shriuker and stretcher consist of a block L, which is part of the main frame A. On the back of this block, there is a projection M, agaiuat which the tire rests, I and which is provided with teeth at the end u as u>

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