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„.i by many who have been looking expeotontly for hie "Second Course."

"HoKK's Secret Code for Letters or Telegrams."

G. Hogg, and Co., 122, Fleet-street. This secret code is a more perfect development of that issued two months hack on a card by Messrs. Hogg. The present plan eaves considerable trouble and time to persons using the code, and an important improvement in the secret notation for figures considerably enhances the value of the system. The chief merit of the corte is that its application can be so changed at the will of the sender or receiver that it is impossible for any but themselves to read tho message or letter sent. The same message can be written in thousands of different ways-that is ta say, tluit fifty people might telegraph the result of the boat race, and none of them should be able to read the others' messages, though all sent on the same system and in the same words.

cut the screw, 4o., in tho lathe; but thin was a needles« refinement, as a «lit carefully made with a very sharp penknife in a piece of latten brass will answer all the purpose. Particular саге should, however, be taken to remove every trace of rnggedne« from its edge as every little excrescence will produce a dark line parallel with tho Ungtk ot tho spectrum. It is almost needless to add that the box itself mnst be densely blackened inside. The mode of nsing Uns primitive npparaiu« will be obvious. Directing the slit to the source of light to be examined, tho prism is turned round Ob Its axle until the spectrum I« plainly seeu. and then if we arc regarding Sunlight, daylight, or moonlight, several of the most conspicuous of Fraunhofer'» lines (p. 172) will be perceptible enough with a little attention, to the naked eyo. Notably I). K, b, V. and G will be apparent like trausverse shadings with a lead pencil. An exceedingly slight rotation of the prism on Its axis will be essential to obtain the best definition of the individual lines separately, as they are not all prccbely In focus

mode by whtch Mr. Hugglns determined the rate of motion of Sirius from the Barth. I will, fir, having obtained your permission, endeavour at nn early date to render this somewhat abstruse subject as apprehensible as I can do, without the aid o» mathematics, Id the shape of an article.

A FELLOW OF THE liOTAL ASTBOXOMICAL SOCIKTV.

LETTERS TO THE EDITOR.

OPTICAL AND SPECTROSCOPICAL.

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Bib -If " О G." P. 282, can obtain access to an achrom» 1c refractor of Dallmeyer's construction will direct it to tho Moon, and *TMив carelullyon her

ml, ■ then if moving the rack tube inwards do no prouùce^ pirpTe fringe to the edge of the image, and Screwing It outwards a green one, 1 can only•say that he must be the subject 1»»2«*И"^Й hl Indues» Of course all the outstanding colour Is at «S to the irrationality of ^»"«»eLÄ l.nt the aimof the ontican is always to unite the extreme bright rays -ami tpractice, such discs of crown and

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appearTtoaÙiuÄunt detail of every "esmption.

All the German glasses I have ever seen havo Decn,

more or less, over-corrected. ,,.._,„ „ _ Orí Is

The test of the "Optical Bricklayer p. Я», «

^«rretv •■ crucial one. I think, were I he, that i

wo"w repVt'ullthnae watch dial»1»»«^

should be shining at the time : or, if he knew exactly

whatto look for, he might try the reflec ion of tl .

Evening Sun from the bulb of a thermometer, and ■ «

what sort of a figure the artificial star thus produced

presemcl Stillfif small print and the ЬИИеЫ

engraving were" well eeflned, clear and black, w th

«ufauy appearance ofmist," hi. speculum cannotbe

a bad one under any circumstances, and may be a very

e^NorntheTl.iSht,"(40,. p SM, appears to labour under a very curious misapprehension as to what uewralnês tie size of the field of view In a telescepe; inasmuch as he says. apny„,ol ^Gregorian, that •'there isastrangely small field, not Wrgerthnni he field of the eyepiece itself, when detached from tie body of the telescope!" Why, of course this field fSSZ, Ыгп,ш,Ы iy th< of Ms *W«« the Je«« if кит must present the same diameter totbeeye, whether the eve-plece be looked through apart from, or in connection with the telescope. As for remedying the defect of which your correspondent »JpWu. И seem, to me that, in all probability, hllleTJ-Wl to« small one. and of course will only take an eyepiece having lenses of small diameter. Ihese again will not ut without a stop between them, and this, ¡a тгсЫШ,, must be smaller still. The distance of lie lenses apart, hasnothlng todo with it. In t he H )■ ghenian eyepiece, it Is absolutely essential to its achromatism that they lie separated by a distance equal to half the sum of their focal lengths. If practicable, an eyepiece of greater diameter with, ot course, a larger stop, would give " Northern Light " a field of increased sine; but is he quite sure that it would be perfect up to the edge? Depend upon It, the reflector maker had good reason for confining the formation of his image to the central pencils. ««.„„„л

I have to thank Mr. Vivian p. 307, for hi» reference to that wonderful old repertory ot Information, •• Smith's Optics." The mode given of finding the focal length of a concave lens is sufficiently simple, and its reason evident; but still it would require one to think It out before arriving at it. Not so wi liitoe second method, given by Mr. Prestor. on p. 809, that of combiulng the lens, whose focus is to be determined, with a onv-ex one of known focus which ought to havo occurred to me merely by the light ot nature. Why it did not, it would not be fiattenn» to

myself to bint. . ., .

Without giving another paper on tho construction or the spectroscope. It may suffice for tho present purp os of Mr. II. W. Bishop, (4004), p. 287, if I inform him that the simplest form of spectroscope, if it be worthy of that appellation, with which I am acquainted, is one which I proceed to describe; and which consists merely of a prism at one end (if a small box about afoot long, which has a silt at tue

other end of it about —in. wide, and a Jin. in length

80 .

parallel to the refracting edge of that prism. An eyehole »loped upwards serves to direct the eye to the mingo of the spectrum. In the annexed section of this alliiir, В represents the box, S the silt running parallel to the width of the box, P the prism, and E the eyehole. In the case of one which I constructed myself some time ago, I made the silt with two knife edges separable by a fine threaded screw. The knife edges I filed out of the old brass scale off a broken thermometer, and it took me all one afternoon to turn aud

seen, tin common spirit lamp тн ■ишиид Bbivuu its wick be flashed across the slit, the brilliant yellow line of vapourised Sodium will be superposed on, and entirely obliterate its corresponding dark absorption line In tho Solar light: iu fact, so universally diffused is Sodium that it is almost impossible to make this experiment without nny salt on the lanipwlck at all, aud yet not have this line fiash up, as the flame crosses the silt. If instead of viewing Sunlight, either director reflected, we look at that of a lamp, we shall get a continuous spectrum, uncrossed by any lines whatever.

A more elaborate form of Instrumont on tho principle of the one figured on p. 115 may be constructed by the aid of a prism of dense flint glass, (or preferably of a hollow plate glass one, filled with bisulphide of carboni, placed vertically in a wooden box, as represented In the next figure, where В represent» tho box with the top removed, P the prism and T and I" two telescopes. The eyepiece of Г is removed and replaced by the disc carrying the slit S, this must bo accurately in the focus of its object glass O. As in this rough form of spectroscope, it is difficult to devise a means of giving motion to tho telescope T' through the necessary arc. the prism itself P, must turn on its axis. It will be understood that the inclination of the axes of tho

ASTRONOMICAL.

Sir—In answer to Mr. Albert P. Holden. (404). p. 311. I may say that I know of no printed observations of rtJrtll Majoiis since thoseof Kaiser in ISM, when ho made the distance;! '0«: but that the components urecerlainlvmuch closer than that now. 1 should be tempted to think from memory of my last peep at them, under l'S. My Kqustoreal clock has taken what the Scotch call "a dour tit" just now, and decline! to drive the telescope, or I would make a fow mlerometrical measurements ot the distance and po-ltlon of the two stars £ Urea», for Mr. Holden'» benefit.

With reference to Ids query about the "Bar Micrometer " I must candidly confess my Ignorance of it. I am very familiar with the ordinary splder-llne posi_ tlon micrometer, the one I always now employ, and likewise with the double Image form of it, and I alio know the ring micrometer iwhich, by the. way, Is the cheapest form of Instrument I am acquainted with), but 1 never saw a bar micrometer In my life, nor do 1 know what It means. I eu-pect, however, that it. depends on something the same principle as tho rlmr micrometer, and Is used to determine Hie plaot-sol Stars In the heaveus differentially. Where, or by whom, may 1 ask, did Mr. Holden, see or hear It mentioned 7 A Fellow Of тпе Eoval Astronomical Societv.

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CONGRATULATIONS. , Чт — Lot me add my name to the long list of those who appreciate the effort« you have made to make the Fnc.i.isii Mechanic thoroughly worthy of Us wide circulation. 1 cannot say that I havo been, very successful in adding to the number of your subscriber» for this simple reason that I And all my friends are already subscriber». I do not say I am chut you aro about to absorb the Samtific Oui**», for I think t deserved to succeed in establishing Itself n publie favour It was well designed and excellently edited, aud hail not its plan been very coolly appropriated by about the worst edited journal I know of (one which you will doubtless absorb before lougj would have been I imagine, completely successful.

I cannot bui congratulate you on the skill with which vou manage the Correspondence column» I do not think It would be by any moans wiee to rigidly exclude letters from paradoxlst», or, generally, from writers who do not very closely attend to tlio-e precents of Montaigne with which you bend the Le ter columns. But while kindly suffering the weaker brethren to speak, you yet make them feel that there »re limits within which they must routine themselves. No one who has followed the progress of the) English Mechanic for tho last few months eau have failed to recognise a gradual change of tone. Those whose eole object. Is to impart useful information feel encouraged to use your columns i,,„re and more freely; those who mistakenly, but honestly, imagine they have much nseful knowledge to Impart, are gradually finding their level-and l«t^.'hos« who would use your colunias to "blare and bellow forth their own stupidity" are steadily discouraged. The result is, that your subscribers can turn with confldonco to vour pages for sound Information on а ver" wide variety Of subjects. I have not lately seen a number of yours in which, quite apart from the set articles I have failed to find many a good twopennyworth of useful information ou a variety of subjects m which 1 take interest.

Ricuabd A. Pboctor.

two telescopes to one another must be at all events | approximately suchas to give tho minimum deviation for the mean ray of ihe spectrum. Themodeof using this instrument will be practically the same as that of emploving the form depicted and described on pp. 145 and 146. Any two snail achromatic telescopes will suffice for its construction, and a prism being formed of accurately-fitting pieces of plate glass cemented with gelatine londa very little glycerine), and tilled with bisulphide of carbon, will complete the whole thing. Particular care must be taken to free the edges of the glues from grease with some Birong alkali , or the gelatine will not hold. The carbou bisulphide is, I think, only about half a crown a pound, anda very few ounces would fill apriein large enough for the spectroscope I am describing.

Having written which I am confronted by the query of " W. K." p. :S06. To him I would say, if be, as a chemist, have any intention of working practically with the spectroscope, let him not attempt to construct what, after all, must be an imperfect piece of apparatus, but go straight to Mr. John Browolug, of 111, Mluories. London, and he, for five guineas only, will supply him with the form of instrument of which a wood out hue been given in p. 145. "Koscoe s Spectrum Analysis,"or his " Klemcutary Chemistry, published by MacMillatl and Co,, London, will give all needful detail to enable your correspondent forthwith to set to work. The rest he will soon succeed in doing for himself. To return, however, to Mr. bishop, The soluiious for the observation ot absorption bands ordinarily recommended to beginners are Blood, Madder, Permanganate of Potash, Magenta and Chloride of Uranium. The micro-spectroscope is more particularly adapted to this form of investigation. Iodine is the torm of vapour, and (as noticed very many years ago by Sir David Brewster) the red fumes of nitrons acid gas gives strong absorption bands. 1 confess that the mode of making a "Solution of Sodium " tloes uot occur to me.

So much for the spectroscope itself. Willi reference to the reiterated request that I should de-crlbe the

LEIGH'S PLAN FOR CONVEYING КAILWAI TRAINS ACROSS THE STRAITS OF DOVER.

Sin -In the ycarliWU, I first conceived tho Idea о conveying railway trains across the Straits of Dover ami took out a patent fur it, connected with «irn, other nautical matters. In the following year exhibited my patent ship In London to the Lords r, the Admiralty »ndannmber of other scientific g 'title men including Mr. Scott Russell,* having been Intro Suced to most of them by Rear-Admiral Penman After this 1 sent my models to the Greot Exhtbttlo. of London in that year, and distributed hundreds a lithographs with a printed description of my noi I ship showing how railway trains might be convoye across the Straits of Dover or other narrow sea».

Л project has since been formed, I believe, by M John Fowler, for a similar scheme to mine. I »rot ,в)1г Fowler, stating that although I had a paten •ma пав the flret Individual to invent the plan. I lia no wish to bo au obstruction, but was ready to de. with him on suitable terms, or join him In iheentot nrise To this letter there was no response. Iwrni again in Januarv, lSt>7, and was informed that M Fowler was then in Italy, and that my letter wouI be luid before him next month, on Ills return. I bear no more. On the 17th of February last I »t» again, expressing the same sentiments, but he has \v

re{ttre( Fowler has of course a perfect right to can out any scheme of his own for this object, so lone; he does not Infringe my Patent: but why he 'bou "о such a roundabout way to avoid this, if it can shown to be better than his plan, is nconcelval except on a certain hypothesis, the nature of which leove my readers to Infer.

The public tire very little concerned as to who jtii have tie honour of the scheme, beyond the love of I, play; but they are greatly concerned about having t

• Since this, Mr. Scett Russell has partly carri this plan out in Switzerland, where a »team ferry established for conveying trains «cross the Lake Constance. It has also lately been partly carried о In America, by conveying train, across a broad rlvi

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LEIGH'S PLAN OF CONVEYING RAILWAY TKAINS ACROSS THE STKAITS OF DOVER.

best method and accommodation. Now, if it could be bhown that Mr. Fowler's plan of shipping and unshipping the traîne wae better than mine, and his bout taeudier, 1 should have uothlag more to say; but I Aubmit it in eo much iuferior that the public ought not to put up with the Iocs of time, delay, and inconvenience it would occasion. I alio do not think that the plan of boat which Mr. Fowler has shown in EiiJjineerhty and other publications, Is the beet Hint can be devised for this object. There appears to be no originality about it. It is merely a large paddle Steamer with the wheels outside. How such boats will fare In the Channel in stormy weather will be веси, if they are ever made.

The boat (Figs. 1, 2, and 3) which I have designed for this service will not draw moro than seven or eight feet water at most, with train and coal on board, ! if made without the pontoons ppp Fig. 'Л, and only 'about twelve feet with them. The paddle-wheels work (ae shown) always in smooth water, which, by the peculiar construction of the wheels, is always 1 kept at the outer perhiphery, so as greatly to economise the power given olf by the engines. The general «piiuclples in the cellular coustruction of this boat, . ensure the greatest possible strength and safety with .the least possible weight. It is also calculated for a • higher rate of speed than has ever been attained 1 btfore. The engines are extremely light for the power j given off, in consequence of the high velocity of piston ( traverse which the priuciple affords, without being too often on their centres. Steam expausion may be I carried out to the utmost limit with the greatest convenience, as a very long stroke may be obtained, I thereby ensuring an economy in fuel hitherto unknown . in marine engines.

It will be seeu from the light draught of water and . the general plan of entering the harbours, that ft will be quite unnecessary to change the present routes rio Calais, Boulogne, or any other port, as there is a sufficient depth of water at all times, Л small islnnd marked i on the plan, is thrown out at sea, in front of the harbour. This island is about the size of the '.train boat, and is formed by filling and sinking a shell boat with concrete. This shell must be made to conform to the depth of water, which, first being moored ( to its place, must be gradually filled aud sunk. The .bottom of thle shell may be made like a series of arches or tuneéis, во that a curreut of water may flow ito prevent the possibility of silting. On this artificial inland is placed a lighthouse t to guide the train • boats into the harbour. The island is so placed that -aboat can enter the harbour from either side with equal facility, so that the train boat, before entering ff rom the rough sea, cau take the lee side of the island, right or left, according to the weather. By this arrangement the great loss of property and dissatisfaction that would en MR1 from the desertion of Calais ,aod Boulogne, would be avoided, aa the harbours themselves may be formed ou the same principle as the island in places where there is not sufficient water kit present; und altogether I submit that there would Jbe a vast saving of expense, compared with Mr. Fowler's scheme.

The accompanying plan exhibits eure and perfect sounection between the ralle on land aud those ou

deck the moment the boat touches the lending stage, as will be seen on reference to Figs. 1 aud 2, and in in which a is a bridge firmly hinged to fixed supports b Л on the land side, and to a floating support с on the landing stage d. The centre of the hinge U in aline with the surface of the rails r, and the bridge with its rails is level with the rails on the land and those on deck at half tide. At low and high water respectively the bridge and lauding stage assume the position shown in dotted lines. There is an indent :in the landing stage r/, iuto which the bow of the boat fits. At the bottom ot this indent is fixed a roller e. The bottom of the boat comes upon this roller ou entering, which causes the landing stage to be depressed a little, or the bow of the boat to be raised sufficiently to bring the rails in an exact line, notwithstanding any little inequality that may arise from light or neovy cargo. The moment the bow of the boat enters (his indent it is caught and firmly held by the catcheä ff, Fig. 1. When the train Is on board these catches are withdrawn, and the boat is at liberty to move off. Thus it will be seen that, when a train arrives, it can be run on to the boat at once, and be carried away without a moment's delay, whatever be the state of the tide. The same in unshipping the trains.

The construction of the ship combines immense strength with the greatest simplicity, reducing shipbuilding' to one uniform principle, for large boats especially, being merely a multiplicity of similar parts, cellular below ana for some diHtance above the water Hue. To sink such a ship from mere accident Is impossible, at the same time the expense of construction is reduced to a minimum.

Mr. Leigh's improved plan of steering the boat is as follows:—I place a helm at each end of the ship, making stem and stern alike. These two helms I connect together In such a way that if the front helm is turned in the direction the ship is required to go, an immense pressure of water comes against it; the power derived from this Is transferred to the aft helm, which it brings up in the opposite direction like the head and tail of a fish, and the vessel swings round with the greatest ease. The helms being in equillbrum a boy may work them (see Figs. 4 and 5). It is obvious, however, that no helms will be required for boats having detached power, as they will be steered by throttle valves, except in the case of accident to the machiuery.

Altogether I am prepared to prove that my plan of boat will be much swifter, steadier, saler, and cost no more than au ordinary boat with outside paddles. I calculate the passage will occupy only fifty minutes in fair weather. I also conteud that my plan of entering the harbour, shipping and unshipping trains, will be more efficient, and cost less than the method shown by Mr. Fowler; but of this I leave the public to judge.

Evan Leigh, F.S.A., Manchester.

TOURISTS' Trips.:

SCOTLAND.

going for a tour In Scotland, in .luly, for two or three weeks, and should be glad to see information from someone wh > has been for about that time. We have "Bradshaw's Hallway Handbook for Tourists." Sections 3 and 4, but there are so many place« of Interest that it isa difficult matter which to choose.

Scotia.

DEVON AND CORNWALL.

Sir,—X should like to take a walking tour along the coa-i of Devon and Cornwall, add there are m.in y others who would do the same if they knew the most economical mode of doing It, and as, no doubt, very many others would be Interested in read lug hintto walking tourists, aud more particularly if geological information be given, I should be glad If someone who has been in this part with stout shoe* on, a walking stick iu hand, and a knapsack on his shoulders, would give us in as small a compass as convenient, the result of his experience. By-the.way, I think that tourists who are readers of the English Uechanic will «ot fail to say a good word In favour of our friend and councillor, as they g 5 on their holiday rambles.

COCKNET.

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SCARBOROUGH.

Sir,—As some of your readers take an interest in collecting birds'eggs and shells, I may say »Scarborough possesses some rare advantages. Our beautiful and gradually sloping sands aro quite attractive to the shell seekers, and remarkable for the number of specimens they produce. We are also highly favoured with a variety of birds, as a proof of this I may state that in the short space of six weeks I have collected fifty specimens of eggs all of which have been taken within a very few niiiea of Scarborough, among themis the curlew, the sea parrot, kittywakos, razor-bill, guillemotes, cirl buntiugs, flycatchers, Ac, &c. Andas for boating aud Ashing you may enjoy that to your heart's content, thus think how delightful it is to go early in the morning, when the sea is as smooth аз glass, taking your shrimp-net, with you, and your box of specimens, enjoy a good bathe, and thea after having obtained a good collection, coming hack and enjoying a hearty breakfast, of hot rolls, fish, &c. Then the programme for the day is arranged, a visit to the Old Castle, built in the reign of Stephen, by the Earl of Albermale; the walls ot the ruin, 9ft. thick; and then standing on such a bold promontory, ."100ft. above the level of the sea, the rocks direct beneath you, and here we sit down and rest awhile, watching the Naval Reserve men or the Artillery firing at the target that is anchored off. Then there is Oliver's Mount, 500ft. high, and one mile from the town. We get to the top without any difficulty, and then what a sight breaks on our astonished gaze.

Away I away!—as far as the eye can stretch, the

waves and the sky seems to touch. I thiuk I hear some of your readers say, " Ob, yes,

this is all very nice, but what a long purse you re

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the reach of етегу working man, this lifc

soul-renovatlng enjoyment. Tbe railway

IB by the excursion trains are very low indeed.

'i most comfortable lodgings, within three

'walk of the sands, can be obtained for the

xee of one shilling a day—that is for bed and

sitting-room, and cooking and victuals—one

r clears all; the charge for bonrdlng and lodgings

hotels is from es. iki. per day. Should any of

readers want any more information I should be

; happy to render it.

W. W. I.uiKiN, Scarborough.

SUMMER SCIENCE.

Sir,— I am goine "to do and exercise" us the lawyers say, the Englishman's grand privilege, in fact the privilege of all British subjects, the mainstay of our institutions, Ac ad lib.— t bat is. to grumble. My cause of complaint is this, your paper is too scientific for the time of year. "All work and noplay makes Jack a dull boy" saith the proverb, and if those words be studiously thought over during the winter (you can't think in hot weather), they will be found to contain more real knowledge of human uaturethan many of the voluminous essays that arc inflicted ou us "poor casses." Certainly you had a note of a tour in the Western districts of Ireland, but then all your readers are not in the position, or have not tbe Inclination to travel that "side of Jordan." You possess, I suppose, readers in every town of the kingdom ; well, let one whole capable of doing so in each town, send you a short note of the ancient buildings. Ac, that the town possesses, that are worthy of a vieit, so that any of your readers when taking their summer outing, no matter in what direction, may have something to occupy the mind as well as the body, and afterwards call up pleasant recollections, which are more than can be said of poring overplus, minus, &c, this time of the year. Take London. You have, I should say, a few thousand subscribers in this—well, call it city, modern Babylon, or what you like. See what interesting and at the same time picturesque and historical pinces there are around It. There is Keosington, for example, with its Palace, Lord Holland's Park, Ac, while Twickenham, and all up the river, bring recollections to mind of Horace Walpole. Pope, Sheridan, Fox, Burke, Ac. Not only would these notes possess a passing interest, but if carefully written and unnecessary verbiage dispensed with, they would possess a luting value, and, like a thing of beauty, be a joy for ever. Jf any of our sternly scientific correspondents like to treat the subject in a purely practical manuer they might do so with great gaiu to themselves and their readers. For instance, there is Willesdeu cage, whence, so tradition tayeth, that uoble hern Jack Shepherd escaped (by the way, what a striking picture this would have made for the Police ffeict .')■ Well, that could be treated of in a purely scientific manner, and \re might have stated for the benefit of posterity the actual time the hero took to accomplish his feat—In fact, the number 'of; tquare inches of brick, wood, Ac, disturbed, anda calculation of the power of the leverage employed would be very interesting. But let us have no Beardeleyism. Human Science is all very well iu the winter, but in the summer let us have the Science of Nature and the matliematicsof green fields, rippling waters, and all those other sights and sounds which speak even to the hearts of the most ignoraut of Him who clotbeth the lily and careth for the sparrow.

A London Subscriber. ['" A London Subscriber " Is thanked for his suggestion. He will see by reference to our last number that we anticipated him. Perhaps he can do something to promote thecuitivation of what he calls "Summer Science," by writing on soma of the Interesting objects in and about London.—Ed. E. M.]

GEOLOGY.

Sir,—I am glad to know that wcare going to have а course of letters upon geology. I havu travelled in some of the high and lowlauds of Hugh Miller, Derbyshire, Matlock Bath. Crich Car. several parts of Ireland—north and south, and in Wales also, but I noticed more " fossils" in West Cumberland than iu any of those places to which I have referred.

I don't knowanything more interesting and instructing than that of sittiug at the mouth of a coal-pit (which the miners are uowly sinklugi, and watching and examining the materials that are brought from below—say SJUft. or MUtt. from the surface. I have done so on many occasions in West Cumberland, where I collected more than a cart-load of fossils. A considerable distance along the coast there Is a large space between high and low watermark, from which numerous fragments of fossils are washed up by the action of the sea, which I have oftcu picked up.

Veritas.

LOW-WATER DETECTOR AND SAFETY
VALVE.

,э,|||—I extract the following account of nn ingenious device combining a low-water detector, alarm, and safety valve, from the Scientific Amtncaa.— The safety valve is made as shown in section at A, with a flat ."unuiar face, tu upper portion being nearly at right angles with the vertical part, and a tubular opening passes through its entire length.

Into the lower part of the bent tubular opening is screwed the vertical pipe li. and Into tho upper part the inclined pipe C, harlng at Its outer end the hollow sphere D. I'ho sphere D has a pet cock at the top to allow the efflux of air when the valve Is first adjusted u> work. On tho opposite side of the valve A from the pipe С projects a bent arm E, pivoted at F. and carrying a weight by which the valve can be adjusted tot lie required pressure. The pipe В descends below the normal water-level, aa shown.

Iu adjosting this valve the pet cock in the sphere D i" opened when the air escapes, and the pressureof tho »team upon the surface of the water in the boiler '■anses the water to rise and till the cavity. The weight upon the arm E is then set to counterpoise the »eight of the water to the pressure It is desired to

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maintain. Ллу pressure exceeding the required pressure raieee the valve and relieves the boiler. It wilt be almo evident that as eoon as the water falls below the pipe li, steam will take tho place of water in the pipe С und the sphere D, and tho valve will then open immediately. The sound of the steam, as it issues from the valve, will give the alarm, or a whistle may be employed if desired.

In this case the valve is opened by both the force of steam and the counterpoise, nud a very wide opering being made the discharge of steam will bo so copious as to he readily distinguished from the smaller escape due to pressure alone.

P. Humphriy.

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cast iron, iu one piece, bearing- :i short leg« to stand on, and a Jin. ball in centre screwed; li barrel of pump, G handle of piston and piston rod, D small Cock to equalise pressure where required, also to allow of vapour oi liquids or of gases to enter the receiver when exhausted. I use a disc of very thin vulcanised rubber between pnuip, coil, and receiver, they requiring no luting of any kind to keep them tight, wiiivh isof great importance; there are 2 valves E E. What I use Is thin vulcanised rubber, or oiled siik will do. Fig. .1 is an enlarged section ot valves; the rubber or silk is bold upon tbe aperture with a silk thread

wouud round the 2 ends of rubber when folded over it; the piston rod is mado of brass tube ; the uuder end carries the top valve, the other fixed in bottom ot pump; tho piston is made with 2 cup leathers, back to back, about i im. depth. As to the vacuum this pump cau force, 1 attached the tube Fig. 2 to plate of pump altera few strokes to shut the small cock, then disconnected It from the pump, opening; the cock under water; it filled the tube to about | of the top, the length of it being Hin. The vacuum is such ae to produce Gassiot's Fountain in a satisfactory way. But let me here remark that although this sample pump works very well, 1 know that there are others that are far superior to it if the cost be no objection. But here n might be as well to state size of coil and battery employed iu producing those experimente. The coil coutaiued fully Mb No. 28 of secondary copper wire; a Grove battery, the platina plate 3 by Шо. spark in free air ¿iu. ; the coil has no insulation, but the cotton covering with a coat of shellac overall, but is wouud by beginning at one side of bobbin, which is «Ыз, and filling the under corner first, then up and down till the whole length is filled, thas removing the ends to the greatest distance from each other. Now, Sir, as to the length of spark got from my coil compared with that gUen last week by "lnductorium," it must be far superior to mine if length of spark without reference to thickness is to decide the point. Haviug.thus far endeavoured to help a brohter 1 trust lu '• luductorum" fulfilling his promise, so that Í may lengthen my spark.

At p. 181, "Tangent" gives details of a contact breaker, which, by-the-bye, he thinks will hardly do for experimenting. What does he mean to do with it? I have looked it over but am at a loss to see how it is to work. We were to have a description of a Ithurukorll from linn, nud I feel hopeful and trustful of hearing воои from him or some one upon this point. it having au important action iu the worklug of all coils.

A. Farquhar.

PHRENOLOGY.

SiK,—In reading over the communication I sent aad which you have inserted in the Mechanic, 1 was much amused by finding lump substituted for bump. 1 think it must have produced a -un le on the countenances ot your readers. In reply to what you say as to whether phrenology would enable a person to distinguish between the six different characters mentioned, I think it is tod much to expect, for the following reasons :— The preacher might have a phrenological development so varied and comprehensive that he might have made и good engineer or successful merceant, or a clever statesman, or л botanist, and possibly a poet; but owing to the Influence of circumstances he becomes a preacher. This being the case. It would not be possible for any person to say what he was. You might as well introduce half-a-dozen men, one ablaoksnilth. one a joiner, another a painter, and soon, and ask a

f>hreuologist to decide what they all were. A phreuo ogist would tell on examiuation whether the person ■ \;¿miued, had the necessary organisation and deve

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lo .ment to fit him far becoming nnengineer merchant Drcaeher &c, bnt ho must not be blindfolded, ns he Ж .lot judge of temperament and hereditary organic quality, io necessary to form a correct opinion ït le just as necessary to ascertain the quality oí bram ns the comparative size of the »rgans.

Yon may depend upon It, phrenology Is a true sc enco, and founded on facts, and if generally understood and acted upon, would be of great service to mankind. An Inventor And Self-taught Mechanic.

Г Does not our correspondent givo np the whole question when he says that "the poacher might have a phrenological development so varied and comprehensive that he might bare made a good engineer or a suciesaful merchant, or a clever statesman, or a botanist and possibly a poet, but owing to the influences or circumstance« be becomes a preacher " .' I Ills shows that circumstances determine for him; these circumstances mar he education, scenery, climate, society, marriage ora dozen other things that influence a man s Ufo and character. Our correspondent goes on to say that "it is as necessary to ascertain the quality of the brain as the comparative size of the organs." . lie must admit that the quality of the brain Is also influenced by circumstances such as diet, habits, education, religion &c. But how can he ascertain the exact quality by any partioularconfiguration of the skull?—Ed. E. M.

TRADE AND COMMERCE. Sm,—Last week I sent you a letter deprecating the discussion of these subjects in the Mechanic. To my great dismay I find that my unfortunate essay has had tho contrary effect of producing a column of matter in tills week's issue. Although unsnrc-ssful, I am not discouraged, and with your peruni-slnn will make one more effort to show the inutility of the discussion of so great a subject upon so email a seal«.

"Herbert's" letter, being simply a reiteration of hi» former one, requires little comment. He still insists that the balance of Impone over exports is clear profit, but his imaginary cargo does noi prove this 1н ihe slightest degree. Supposing that through a failure of produce in any one year wo wore to run short of provisions this would clearly ben loss to us. hut by "Herbert's"course of reasoning it would appear to bo so much profit, since having ю buy our provisions from foreign countries, our imports would exceed our exports to a much greater extent than usual, and the year which w»s realty the most disastrous to the nation would appear to be the most prosperous. It may beoejeoted tbat the balauce would right itself In the oourse of time, but it ia poor consolation to reflect that" It will be all the same a hundred years hence."

Or, to take another case, suppose that through n long course of unexampled prosperity tlio nation ha<l become ao rich that it could retire from business altogether, Investing its capital in foreign stocks, and with the dividend» purchasing all it» requirements from abroad, the couu'ry might bo turned Into a vast flower garden, and produce absolutely nothing of any value An extension of tho volunteer movement would provide brigades of railway engine drivers aud porters, brigades of gardeners—unpaid brigades to do all the work, but there would be no exports, and this sort of thing might go on so long as foreign nations paid their dividends and refrained from going to war with us. But all this time the nation would be importing goods, and, as" Herbert" holds that trade is barter, we should be in the happy position of receiving all we required and giving nothing in returo. 1'his is taking an extreme case, out tho principio holds good in any lesser degree.

All "Herbert's" arguments are based upon tho assumption that trade is barter, but he does not attempt to prove it. I f he could show that it is a fact, 1 should agree with all of his deductions.

"Sigma's" letter is a gond illustration of the futility oí discussing so large a question in your column», since, In talking of mere buying and selling, it is obvious that we are only skimming the surface of the subject. In spite of Napoleon's saying, we are not anatiou of shopkeepers, as that would imply that we simply buy from one foreign country and sell to another, a kind of business which would never make u» a Îroaperous nation, or Hud employment for our people, n order to nourish, wo must manufacture the goods we sell: aud to be in a position to do so, we must take

be nn unmitigated blessing to this country, but. fear that we shall not obtain it so loig as foreign nations find that ihey can close their markets tnmr goods, and at tho same time retain the inestimable advantage of selling us their own manufactures without restriction. , ,, ,

Years a<'o, when the subject was under discussion, the advocates of one-sided free trade—Iree-trade halfbound, we may call It-were wont to tell us that I! wo only threw open our owu ports, soon all the world would follow our example. We tried the experiment, and now, twenty y ear« at ter, comes the answer from America, in the shape of tho most prohibitive tariff that was ever Imposed.

VELOCIPEDES. SrR—I Hketo seo ¡ustlco done, and "honour given where honour is dne." to every kind contributor of a "brick "in vour valued columns, and witli this obieut I would" draw nttetitlon to tho fact of the designs ¡.itlie" English" Velocipede, by " A Thinker,' (No 26,1-4) and aleo the "Macclesfield Velocipede, by 1. Stanley (page не,No. ¡¡til), being almost (if not quite) identical with the plan invented by .Mr. J. Hasting», as described most fully by that gentleman in 1KJ18 (page 55 No lSVi and by a momhorof the High Peak Velocipede Club, pago 647 (No. 2>fl), which is there stated to have been in use " some considerable tune, so that unless " A Thinker" aud Mr. Stnnway, have been asleep it is difficult. to understand how they both could be Iguorantof tho numerous communications, which Mr llist.ings has kindly given us upon every point and detail of his apparatus, in reply to questions extending through the files of the English Mechanic for two years past.

There is one point, (however, in which these later desiirns fall short of the original ouo ol Mr. Hastings, in which that ingenious gentleman adopts a very simplejand exoellont plau to counteract the tendency to upset in turning eharply at high speed, by axing two inclined plato» on the front steering axle, by which the machine is inclined Inwards ш.оп bemg turned, which appeared Co bo a valuable idea.

I am induced to make these remarks, because I observe that Mr. Hastings does not take any notice of this ap-aront appropriation of his invention in his good-natured lo'ter in replv to the wild theories of Mr. Reveley. (page 184. No.'¿(18.) 1 quito ugreo w.th Mr Hastiu'j-s regarding the advantage of small wheels as belli«- better adapted to utilise the muscular action of the fegs, which I llnd will endure a quick ami easy effort better than a slower and heavy strain, euoli as is the case where large wheels are used for driving, while the length of the crane must remain tho same. I baveuseda4ft.-wheel velocipede for 3 years, upon which I have been long distance», and obtained very high speed on good level road's, but find such large wheels make the machine heavy drwing, especially uphill, upon these points Mr. Hastiugs has written fully In a qnlet, scientilie aud kiudly tone, in pleasing contrast with the wild, aud too often Impracticable ideas of "would-be" inventors who used to Uli up so much of the pages of the English MeChanic a year or two hack, but who aro now. I am happy to see, no longer allowed space to vemilate their dreams. 1, therefore, feet that the subscribers of the Enclihh Mechanic are deeply indebted to Mr. Hastingrs for his communications and kindness and that they do not wish to seo his ingonuity forgotten or appropriated by other».

C. D. E.

leaves as a salad. In my communication, I sought, to draw the attention of our working friends tu the value of many wild plants that were to he obtained without trouble or cost, and that could be used »a silads, and I maintain thin continental experience justifies the truth of my statement, that many source» of good and choap food are neglected in this country through ignorance or prejudice. I have no partie Лаг partiality for dandelion leaves beyond the unlimited supply to be readily obtained, and the similarity iu flavour to lettuce. •' Taut an" is wrong iu asserting that It Is rejected bynlmosteverybody in this country. In tny neighbourhood I daily see scores of workmen plucking the leaves of this plant, to render their midday and evening meals more palatable. With viaegar, oil. pepper, and dressing, no one can reasonably object to it. The. word "beer" was a misprint, it should have been " beet." I'he seeds of mustard sown with those of the garden cress certaiuly furnish a good salad known as "mustsrd and cress." As regard» onions, I do not consider them a rnhtrAc addition to a bow lof salad, он acenuut of their strong flavour affecting tho breath ; moreover, all alliaceous plant» arereaarded as "condiments " by our most eminent food authorities.

As our Journal largely circulate» among the working classes, 1 think that any information regarding food must prove neeful, moro especially if aitentiou can be drawn to any members of the vegetable kingdom whose properties are not generally known or recognised; however, with refereuee to taste, 1 think we must all agree with Mrs. Partington, that" that Is, after all a matter of opinion."

Beta.

A CUMBERLAND MINER'S APPEAL. If " Cumberland Miner" were to try a mask of shcotmeuil with eyes, say 2ln. or Sin. diameter, of plate glass, or fine copper gnuze, and pliee it not less tliau 4in. or Sin. from his face, I think it would be some protection. Perhaps,if he tries it he will let us know

the results.

Aliquis.

STEAM HAMMERS. Si»,—I have been a regnlnr subscriber to tho " MeChanic, from the commencement, but have never seen article in on steam hammers. I should (eel reader acquainted

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workmen, whose ordinary diet is bread and butter. But it is in the power of the foreigner to shut us out of the field by taxing onr productions. '* Sigma" seems to think that this process Is an evil only to the country which adopts it. But this Is a question which admits of any amount of discussion, for we have no proper dala to guide us. We cannot take any one country as an example, for the selfsame nation may at different times oscillate between prosperity and bankruptcy , between extreme activity of trade and stagnation, without any change in its Hscal arrangements.

"Sigma" considers the dulness of trade In the United states to be a proof of the ill effects of Protection; and It is difficult to disagree with him until, by dipping a little deeper into the subject, it becomes apparent tbat the rapidity with which they are paying off their national debt is an indication of the greatest prosperity. Probably one deduction is as erroneous as the other.

There is little satisfaction to be derived from statistics; for not only are those which aro available wanting iu accuracy, but, as "Sigma " states iu a former letter, they may be made to tell any tale.

I cannot help thinking that "Sigma" somewhat beg» the question when be talks about the emigration of our workmen being au advantage to the country. There ia little doubt that it is better for them to ito. when there is no longer work for them to do, on the same principle that it is sometimes beneficial to a man to have bis leg amputated; but surely it is no advantage to them, or to their country, when the necessity to emigrate arises from want of employment, caused by the* importation of coods made by foreign workmeu, which might happen were our population only oue-h»lf of what it is—which might uot occur if it were double. _ ,

I have not the slightest doubt that free trade would

acting pru..., have a small hammer In our forge, which we wish to make «elf-actlng, but 1 am at a loss how to proceed. ,r

1 believe Messrs. Massey, of Openshaiv, near Manchester, make one of the best, but I am unable to get to see one. A sketch would oblige.

General Mechanic.

SQUARING THE CIRCLE. St»,—Mr. Arthur Gearing has produced a very ingenious diagram (page :!UI) for the purpose of exhibiting a mechauicjl mode of effecting a solution of this question, in which, however, he entirely overlooks the fact that tho base, line of his sectors must alwavs be the arc of a circle, and therefore cau never be máilo to form a stralgh; line. Proceeding to describe the process, Mr. Gearing says—" take the half of the circumference of ilie circle for the length of tho parallelogram," now that circumference can only be obtained from the well known formula, 1 to 31415927, &c, ai infinitum, therefore his quadrature can only be approximately correct.

The area of a olrcle Is the product of the circumference multiplied by half the radius, and by extracting' the square root of that product, you have the side o f the equivalent square. I had bopod the squaring of the circle had been long since out of print, but it seems that it is never todie.

Henry W. Reveley, Reading.

SUMMER SKATING.

Sin,—I have jnst seen your suggestion about summer amusements, exercise, and scientilie pursuit», and need scarcely sav that 1 thoroughly agree with it. There 1» a time for everything, says the wise man. We. can set down and read elaborate articles during the long winter months, but during thu summer month» we want something moro " summery," if I ean coin a word.

As an inducement for others to »end more userai or more scientific matter for the eeasou, I beg to send a scrap on summer skates, 1 have Jnst. takeu from an American publication. "To carry the pleasure of wluter skating into the midsummer months, ha» been the aim of numerous projectors, whose fertilo brain» have brought fortli roller skate» of varied construction and design. Ono of these—¡in American Invention—has its stock or foot-rest provided with a too wheel, a heel wheel, ami two middle or side wheels, the latter uot having their planes of revolution iu line with one another, but are arranged parallel, and on the opposite flanks of a line extendin' from the centre ot the toe wheel lo the centre of the heel wheel. The two middle or side wheels are to be so applied to the stock as to be capable of revolving Independently of one another."

A Frenchman has invented another devioo ot tne same character, but of somewhat different structure, which I lind described a» follows :—" The leg piece is preferably made of wood, such a» ash or oak. lhe inventor attaches it on tho outside of the leg of the wearer with tho pad in contact with the leg a little below the knee by means of a strap, or any other convenient mode of attachment. T > the lower part of this leg-piece be attaches, by bolts and nut», or otherwise a wrought-lron or steel angle piece, to which lie attache» In a similar manner an elastic steel foot piece, »lightly raised at its extremities for supporting the foot and the heel of the wearer. Side joggles serve to maintain the foot laterally, aud straps tu hold it firmly down on tho loot piece. The locomotive wheel Is hung ou a stud attached to the leg piece by a nut; a vertical slot is mude through the leg piecu where thu stud passes, to enable the wearer to regulate wituio. certain limits the height of his foot from lhe ground as well as for the purpose of using dlffereut-sized wheel?, if desired." W R. В

MEDICAL GALVANISM. Sir —As a medical galvanlst of several yeare'experience I beg the favour of a little space iu reply to the lett.jr of .Sir. Anson, in your last, 1 have for years manufactured medical coils, and in answer to his theory of intense currents being unsuited for application to the human system, 1 »ay, us the result of my experience, that in certain савеа an intense current, collected by a (quantity) primary coil ia, in those casos, as much au absolute requirement as the same intense current, with the same coil, would, In other inappropriate case», be an absolute failure. But apart from all difference of opinion respecting the proportion of battery power to coil, and via «"".' am eouvlaced that out of a given number of failures, fully nine-tenths can be traced, no', to the inability of the «nlvauic current to effect the cure; uot to the disproportion of battery power to coil, but mainly and simply to misapplication of current. In a good per centage of the above failures, the patients who give up galvanism as not effecting what they have been led to expect (a consequence of which failure is the number of replies " rt. A." has received Irom persons wishiiin- to dispose of their instruments), bold the conducting plates in their bauds for a geueial uervoua affection, to the foot or feet for an aft'ocilon of tie knee and to the spine for an attack of indigestion, aud so on for a number of cases, which had the current been properly applied, would soou have made manifest trie Immense'amouul of curative property Inherent in g.ilvanio currents, medically and properly applied, ut present hid under tho bushel of medical prejudice ana iguorance of proper application, i'robably Irom my signature, "W. A." may recognise me a» the sender

SALADS.
Sir, -In last week's number, lam taken to task by
Tautau" for recommending the use of daudeliou

of a pamphlet on medical galvanism, iu answer to the advertisement to which he refers, in which he will find that I advocate the employment ot an intereso battery (arrauged for quantity) and a quaullty con, with an intensity and a quantity regulator, so in it any ordinsrily gifted person in.iy so regulate the current as to have a preponderance of quantity (over intensity. or Hie reverse; and should you, Mr. Editor, conaidor a drawing of a good medical machine worth io»*irtico in your pa^e«, I shall be glad to oblige " W. A.,"

and perhaps others, and show my estimation of tin*

P^c. of tbo English Mechanic, by forwarding

ooe- I »frreo with "W. A..*' in thinking that an

immense field Is open (or the introduction and practice

of medical galvanism, and once break down the at

present, impenetrable barrier of medical opposition

and prejudice, and open the eyee of the profesión to

tbe real use and efficacy of a properly-applied current,

and I am convinced (in the event of these almost wild

Improbabilities occurring) that medical galvanism

-will at once take its staud ne a recognised household

and popular remedy, but as matters now are, a large

Î>roportion oí the faculty, whenever they find it in ust* n a family on which they call lu their professional capacity, invariably Bet their faces against it—In the majority of cases without ever having given it atrial, even in a ea*e of a patient most susceptible to its influence—and if they do not positively demand the diecontinuance of its use, they as invariably give their ©pinion—in answer to the question by the patient, as to Its merits—"that it can do no good, and may do harm," which coming from the lips of their professional gentleman, carries an additional weight. This t know has been the verdict In several cases where 1 have had the pleasure of bringing the patient back to robust health, by the almo-t surreptitious use of a properly applied current, the physician ju the meanwhile chuckling over hie supposed cure. 1 cannot allow these few lines to come to a close, without »fating my firm belief and conviction that medical galvanism, united in its proper proportion with the nse of proper medicine, is yet destined to bo the menus of effecting cures which are now either Impossible or are of a protracted nntnre. I shall be glad, ¡Sir, if thi* letter may have the effect of evoking replies pro anil con, but I confess I shall like to see them emanate from pens worthy to treat on so Important a subject. I enclose my card.

H. P.

Sm,—Seeing several Inquiries in our Mechanic in reference to galvanism as a remedial agent in disease, and having had considerable experience and some success in its application—moreover being oouünedtotny room through a severe accident—it occurred to me that I could do worse than employ the weary hours of my convalescence iu (to the best of my ability) Instructing my fellow-readers who doslre to pursue this interesting branch of science bow to proceed therein with good hopes of success.

At the threshold of my subject allow me to make a few remarks upon the subject of therapeutics in general. We most of us adopt and cling to one particular system of medicine, to the exclusion of all others. ííaviug satisfied ourselves that one theory of the henliug art Is right, we unhesitatingly coucludo that every other must be wrong. Having found the system adopted by one set ef theorists succeed in certain cases, we condeinu every other system.

In this, it appears to me, we are wrong. И seems to me to be the business of an inquiring mind aot only Va invent theories, but especially to gather facts wherever they may be found; to nccept truth, from whatever source it may be presented. Kesults. as far as they can be ascertained, should Ы- carefully marked and studied. Special conditions should be industriously noted and observed; und from such material theories should be patiently built up. I

These remarks apply in a more .forcible maimer to the healing art thau to any other science. In this we can never be certain, in any two experiments, that the conditions are precisely the same. It therefore requires a much more enlarged experience, and far wider and more comprehensive experiments, to enable anyone to form deductions in this than In any other branch of philosophy. The constitutions, the temperaments, tbe habits, and the physical conditions of patieuts are so various, that ft is impossible, from Its effects in one or two cases, to judge of the real character of the remedial agent in every (apparently) similar disease. For Instance, In how much mystery is shrouded that very common, yet constantly varying, ailment, catarrh? Who is not acquainted with the philosophy of it? Who is not provided with a remedy for it? from the old woman in the almshouse to the most erudite and intelligent homoeopath. And yet, after all tbe gin and porridge of the sick nurse—the gruel and nitre of the allopath—the drop o( cam

Ehor of the homoeopath—the wet sheet of tbe ydropath—the composition powder of the Coffinltc—the vapour-bath of the herbalist—and the pint-and-a-half of cold water of the teetotaller, how few but what *eem to run their course; and how few, with but little care at first, quietly subside 1 How sometimes, with all our care, they hau g about for months; and how again, when sometimes let alone, they eeeni to die the o/iicker. Yet who would despise the hot footbath advised by all, or »ay that the remedies proposed are no remedies at all?

The science of medicine is intimately connected with that of chemistry. Both health and disease consist largely of chemical processes. When the chemistry of dbca-ws is better understood, the healing art will have made a large advance. Whatever may bo the true system of medicine, tf such has vet beeu discovered, w<? know that nearly all chemical processes are more or less under the control of electricity or galvanism. Ch< mlcal force, as Faraday, in bis " Physical Force?." beautifully demonstrates, is convertible into galvanic and magnetic force, and vice versa; and we know from experience—at least those of us who have ever held the poles of a large galvanic apparatus —that galvanic force is convertible luto, and largely controls, animal or muscular force. Galvanism or electricity is closely associated with nervous activity and life, if it do not actually form the link between spirit and matter. The amount of nervous vitality tn th* body may be guaeed by means of a delicate galvanic pile. Determinable galvanic currents are continually being generated by the chemical processes curled on in the animal economy. Electric currents are constantly circulating throughout the nervous system. The galvanic current is found to poesess a specific power over many of tbe most important functions and teeret tons of the body. К very throb of the brain. rvery pulsation of the heart, every twitter of the ъегте«. Is productive of, ur connected with, electric

excitation. Dr. Bey mon d has conclusively demonstrated that the muscles und nerves, including the brain and the spinal cord, are endowed during life with an electro-motive force. The electric current flows from the great nerve centres towards the extremities. The strength and intensity of these currents depend upon tbe state of health or disease of the bodily subject aud the amount of vitality possessed. In some forms of disease, as tetanus and epilepsy, the nervous excitement is excessive, and the electricity developed by those parts is beyond the normal quantity or intensity, and requires to be decreased. In other forms of disenso, as asphyxia and general debility, the circulating electricity is found to be below the normal amount, and requires to be increased; whilst in still other aspects of disease, a chemical reaction or decomposition should bo set up. aud a current of great intensity and quantity is requisite.

In nearly all cnses'galvanism may be applied as a remedial agent without the slightest inconvenience or pain, and is often most successfully used when scarcely perceptible by tbe senses at all. What is required is a current large in quantity, and of very feeble Intensity. Any machine that is not capable, of generating very large quantities of the galvauic force will, in ninury-Dine cases out of a hundred, be found useless; and such anpllaueos as galvanic belU and chains, which give off but small quantities of galvanic force of very great intensity, in the two former classes of disease, a* I have often seen, are Hablo to become positively mischievous in their effects, though they may occasionally prove beneficial in cases of effusion of maLter into thejoiuts, In rheumatism, and similar forms of disease.

The student should therefore provide himself with an apparatus exposing at least from 12 to 30 square feet of metallic surface, and so arranged as to be capable of producing a great variety of effects, from the very feeblest possible curreut to the strongest of which the machino is capable. He should also bo provided with two coils, the one a single helix of thick copper wire, with a bundle of soft iron wires enclosed, and connected with the terminal wires by the usual glass tube and water arrangement, aud the* other a UlmmkorfT's, or similar coil, capable of giving the strongest secondary efleets. .Some arrangement should alscT be provided whereby the *vhoIe of the cells can have all their positive polos united aud attached to one end of the coll, or) terminal wire, and all their negative poles brought together and united with the other wire, instead of being alternated in tbe usual manner, so as to afford the greatest quantitative effects. Zinc and silver or platinum plates should also be secured, of different sizes, aud with insulated knobs, to take the p lace of the handles, for its more ready application to various parts and organs. It will oteen be found better, in local application, for the operator to allow the current Hrst to pass through his own body, and then with the moistened knuckles «( his free hand to gently rub the affected parts. This mode of application, while more efficacious in коте affections, greatly mellows thi-'intensity of the eurreat, and appears to modtly it In several other respects.

Electricity and galvanism used in this way, and cttm grano salis, will bo found a powerful agent and assistant to Nature in her efforts for the removal of disease; for, after all, we must ever bear In mind that In every caseit is Nature, moved by Nature's God, that works the cure. All that the most skiful physician or the best adapted remedy can do is to remove obstacles and to assist, and will often work wonders when otnpr means have failed. Indeed, if judiciously applied, it seldom fails either to promote a cure or to relieve, and will often (as in the case of obstinate ulcers) give Nature a good start, which she will not fail to follow up to a healthy issue.

Edmuiîd M. T. Tydeman, lu, High-stieet,
Brighton,

EMIGRATION. Sir,—In your last issuo but oue of the English Mschan'c I observed, under the bead of " Answers to Correspondents," a request that Mr. Rogers would communicut« intelligence In connection with emigration to the Western States of America; and as 1 have not observed any correspondence from a namesake, aud haviug supplied something tritliug ou tbe subject before, I naturally suppose I am the person referred to. It is some years since I was in the United States, but I am in communication with seme friends there monthly; aud anything 1 write, culled from correspondence with them, is reliable. I had occasion, some few months ago. to make particular inquiries, for a friend who wishes to emigrate. He has a family growing up, who could just be of uso to him If be went ont; has been educated, aud practiced for a short time, as a solicitor; has been en tí aged in farming lor some years; could command £luuu to purchase land, &c. lie wished to know whether I would recommend him to go to Canada, either Upper or Lower, and from uiy experience (two years' travelling) of that country, I said certainly not. It is a miserable place—winter too' long, all people bmily paid, and rieh people aro not numerous. Most of those who bave a little money have earned it so hard, that I have known pome who would not trnst the best banks in Canada with it, but keep It locked up or hidden in their homed. These arc not people to spend much; and where there is not a good circulation of cash, there certainly cannot be an inducement to settle there. Having written to my correspondent iu Kent пеку {oue of the middle btates?, ho replied that the amount of money in that Mate would bo a small thing, the profession was overrun, land very high In price; but the State of Kentucky was one of the best of tbe middle .States. In Nebraska the laud is cheap, rich, and yields abuudantly. A friend there says he grew beets in his garden, last summer, that wuuld 1111 a nail keg fa vessel as large as a butter lirklni, and that everything giows so in proportion. Wild Iruits grow in abundance, and a tremendous emigration is growing on. It is a new State. The capital hat recently been removed to Lincoln. An English colony, with which one of our leading members of Parliament Is connected, is located near the above named place. The public buildings ure now being built. Minnesota is a beautiful Suite, hut cold in wiuter for nny one who likes a warm climate.

Middle Tennessee offers many inducements, but is full of Confederate soldiers. A large number of Swbe aro settling there. For a man who has a taste for fannin« Nebraska Iu every respect is good. There are a good many trines of Indians still In this State, who sometimes give some troable; but they are not so fierce as. they were some years ago. However, a border life bos its drawbacks as well as its benefits. Land rn Nebraska can be bought for from £3 to £6 per acre within about lfi to 20 miles from the spleudid city of Omaha. A person buying laud should become a naturalised citizen to enable him to hold land in the Uulted Otates or to practice a profession in courts. Anyone going to any of these States must not expect to fiud society In the same condition as it is in the» old countries and should go prepared for such change. Sons'and daughters muse work in and out of doors for some time until they are Iu a position to hire help. They must milk, feed stock, learn to mow, sow, and reap. Although society Is not all Ürst-elass, still there are very many first-class people to be found there, especially in the older places. These remarks apply to most of the Western States, and are more peculiarly adapted for those Intended to settle on farms, and who have some capital. Being pressed for time, I must conclude.

S. BOGERS.

Sib,—I have Just seen the lucubrations of several correspondents in your last two numbers, upon the subject of emigration. Knowing your large circulation compels you to %o to press at an early moment, I have determined to write a few lines off-hand. Pray let уэиг readers, and especially those intending to emigrate, beware of the fanciful Ideas which may be mooted, and which would prove every square mile under the suu the most suitable for emigrants to occupy. I believe, yes, thoroughly believe, that the colouiee possessed by England offer the best spheres tn our superabuudaot population. The tirade of " B. W. J." about paying tor fancied security is all moonshine; you are likely to pay much more In the "countries of the south*TM main" for no security at all. Bands of lawless desperadoes go about without let or hindrance in many parts of South America, seeklug whom they may devour. The puerility of tbe authorities is so well known, that every man looks out for himself. "J. G.V description of the Argentine aud River Plate territory is not to me very pleasing. I do not seo how а тай would better himself by settling there. But suppose such to be the case, what are his prospecte 7 No roads whereby bis superabundant produce may be utilised and money gained. Hunting accoutrements and Guacho life seem best adapted to the territory. The choosing a spot bv a navigable river, at least for canoes, is easier said than done. Thus, as J. D. Rogers so excellently describes, we must turn to America ; bv this I mean tho United States. Some of his remarks'! protest agaiust-viz., those directed against the English Colonies. Australia is not too distant, neither is New Zealaud, Natal, or the Capo—countries possessing a climate as equitable and salubrious as any part of the United States. Then, again, wehave Columbia, by no means an insignificant part of the British Empire. Here, then, is enough land to absorb the whole population of the "British Isles," if need be. I admire the energy and self-dependence of the working meuat Mile-end. and have no doubt that they will thrive at their new home, ltut I question if they will fled the laws better. Cortainly If our Legislature was to take more interest In colonial matters very much more good would be the result. Apathetic, careless, fguoront, toa surprising degree ; doing nothing but under compul siou, and even then the least possible work, ignoring the claims of our superabundant population; wasting time iu useless i-quabbbng—are a few of the remarks hurled against our Legislature, now true, may heknown by consulting an article on England and her Colonies by J. A. Froude, in Frnser's for January. I believe Mr. Froude would have no objection to the republication of his article in the columns of the Клоыви Mechanic, aud il this could be done a great boon would bo given to its readers. Oue or two of his last sentences I make bold to extract. Thus he says :—

"That emigration alone can give them permanent relief the working men themselves will ultimately find out. . . . Are we to wait till ourown artisans, discovering the hopelessness of the struggle with capital, and exasperated by hunger aud neglect, follow in millions also the Irish example, carry their industry where the Irish have carried theirs, and with them the hearts and hopes and sympathies of three-quarter» of tbe English nation! If Mr. Gladstone and Mr, Odger are Indifferent, we appeal to Mr. Disraeli. Thin is oue of (hose imperial concerns which the aristocracy, lifted by fortune above the temptations and necessities of trade, can best afford to weigh with Impartiality, &c."

По evidently thoroughly believes In a national system of emigration, in which Government vessels conduct the wayfarer, and Government arms encircle and sustain hitii till the time has come when he »an sustain himself. Of course Government would be no loser In the long run; the lirst expenditure would easily be recouped by various means which, however, I cannot at prescut discuss. 1 Again wish prosperity to the noble workers at Mile-end, a speed? and auspicious departure, and a successful Issue lu their new sphere I

F.R.G.S.

WHEEL TEETH.

Sir,—In auswering a query on the above subject, I had occasion to speak of the Manchester wheel gauge, and attempted to describo it; I now forward for engraving, if y-»u please, what I use in place of the gau^e as ordinarily made. As this last is expensive, coating Via. for about t-Ixteeu rows, divided on box wood, and some more for tbe smaller ones ou и brass plate. To use it. say, to ascertain tbe gauge of any wheel you already have, count tbe teeth,and place tho wheel flat on the gauge where you find the diameter of the wheel covers tho same number of equal parts on tbe scale, as the wheel bu<* teeth. And that line of equal parts is the gauge tu work to for any other

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