"Hogg's Secret Code for Letters or Telegrams." G. Hogg, and Co., 122, Fleet-street.

mode by which Mr. Huggins determined the rate of motion of Sirius from the Earth. I will, Sir, having obtained your permission. endeavour at an early date to render this somewhat abstruse subject as apprehénsible as I can do, without the aid of mathematics, in the shape of an article. A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY.

ASTRONOMICAL.

THIS secret code is a more perfect development of that issued two months back on a card by Messrs. Hogg. The present plan saves 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 code 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 the message or letter sent. The same message can be written in thousands of different ways-that is to say, that 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.

LETTERS TO THE EDITOR.

OPTICAL AND SPECTROSCOPICAL. SIR,-If" O. G." p. 282, can obtain access to an achromatic refractor of Dallmeyer's construction, will direct it to the Moon, and focus carefully on her limb; then if moving the rack tube inwards do not produce a purple fringe to the edge of the image, and screwing it outwards a green one, I can only say that he must be the subject of a peculiar sort of colour blindness. Of course all the outstanding colour is "attributable to the irrationality of the glass employed," but the aim of the optican is always to unite the extreme bright rays; and, in practice, such discs of crown and flint glass are selected as to ensure this union, and at the same time leave the smallest possible amount of secondary spectrum. The effect of over-correction is, in my own case, to give a factitious brilliancy to the image viewed: that of under-correction, to surround everything with a wretched orange fringe, which appears to dull and blunt detail of every description. All the German glasses I have ever seen have been,

more or less, over-corrected.

The test of the "Optical Bricklayer," p. 284, is scarcely a crucial one. I think, were I he, that I would repeat it with a watch dial upon which the sun should be shining at the time: or, if he knew exactly what to look for, he might try the reflection of the Evening Sun from the bulb of a thermometer, and see what sort of a figure the artificial star thus produced presented. Still, if small print and the fine lines of an engraving were" well defined, clear and black, without any appearance of mist," his speculum cannot be a bad one under any circumstances, and may be a very excellent one.

"Northern Light," (4063), p. 311, appears to labour under a very curious misapprehension as to what determines the size of the field of view in a telescope; inasmuch as he says, apropos of his Gregorian, that "there is a strangely small field, not larger than the field of the eyepiece itself, when detached from the body of the telescope!" Why, of course, this field (being determined by the size of the stop between the lenses of the eyepiece, must present the same diameter to the eye, whether the eye-piece be looked through apart from, or in connection with the telescope. As for remedying the defect of which your correspondent complains, it seems to me that, in all probability, his eye-tube is a small one, and of course will only take an eyepiece having lenses of small diameter. These again will not act without a stop between them, and this, ex necessitate, must be smaller still. The distance of the lenses apart, has nothing to do with it. In the Huyghenian eyepiece, it is absolutely essential to its achromatism that they be separated by a distance equal to half the sum of their focal lengths. If practicable, an eyepiece of greater diameter with, of course, a larger stop, would give "Northern Light" a field of increased size: 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. I have to thank Mr. Vivian p. 307, for his reference to that wonderful old repertory of 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 with the second method, given by Mr. Prestor, on p. 309, that of combining the lens, whose focus is to be determined, with a convex one of known focus, which ought to have occurred to me merely by the light of nature. Why it did not, it would not be flattering to myself to hint.

1

80

Without giving another paper on the construction of the spectroscope, it may suffice for the present purp os of Mr. H. 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 pris m at one end of a small box about a foot long, which has a slit at the other end of it about in. wide, and a lin. in length parallel to the refracting edge of that prism. An eyehole sloped upwards serves to direct the eye to the image of the spectrum. In the annexed section of this affair, B represents the box, S the slit 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 slit with two knite edges separable by a fine threaded screw. The knife edges Ifiled out of the old brass scale off a broken thermometer, and it took me all one afternoon to turn and

at once. When D, the Sodium line (p. 172), is sharply seen, if a common spirit lamp with a pinch of salt on 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 the Solar light: in fact, so universally diffused is Sodium that it is almost impossible to make this experiment without any salt on the lampwick at all, and yet not have this line flash up, as the flame crosses the slit. If instead of viewing Sunlight, either direct or reflected, we look at that of a lamp. we shall get a continuous spectrum, uncrossed by any lines whatever.

A more elaborate form of instrument on the principle of the one figured on p. 145 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 carbon), placed vertically in a wooden box, as represented in the next figure, where B represents the box with the top removed, P the prism and T and T two telescopes. The eyepiece of T is removed and replaced by the disc carrying the slit S, this must be accurately in the focus of its objeet glass 0. As in this rough form of spectroscope, it is difficult to devise a means of giving motion to the 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 the

FIC.2

SIR.-In answer to Mr. Albert P. Holden, (4051), p.

are certainly much closer than that now. I should be

tempted to think from memory of my last peep at them. under 18. My Equatoreal clock has taken what the Scotch call "a dour fit" just now, and declines to drive the telescope, or I would make a few micrometrical measurements of the distance and position of the two stars Ursæ, for Mr. Holden's benefit.

With reference to his query about the "Bar Micrometer," I must candidly confess my ignorance of it. I am very familiar with the ordinary spider-line position micrometer, the one I always now employ, and likewise with the double image form of it, and I also know the ring micrometer (which, by the way, is the cheapest form of instrument I am acquainted with). but I never saw a bar micrometer in my life, nor do I know what it means. I suspect, however, that it depends on something the same principle as the ring Stars in the heavens differentially. Where, or by micrometer, and is used to determine the places of whom, may I ask, did Mr. Holden, see or hear it mentioned?

A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY.

CONGRATULATIONS.

SIR,-Let me add my name to the long list of those who appreciate the efforts you have made to make the ENGLISH MECHANIC thoroughly worthy of its wide circulation. I cannot say that I have been, very successful in adding to the number of your subscribers for this simple reason that I find all my friends are already subscribers. I do not say I am glad you are about to absorb the Scientific Opinion, for I think it deserved to succeed in establishing itself in public favour. It was well designed and excellently edited, and had not its plan been very coolly appropriated by about the worst edited journal I know of (one which you will doubtless absorb before long) would have been, I imagine, completely successful.

I cannot but congratulate you on the skill with which you manage the Correspondence columns. I do not think it would be by any means wise to rigidly exclude letters from paradoxists, or, generally, from writers who do not very closely attend to those precepts of Montaigne with which you head the Letter columns. But while kindly suffering the weaker brethren to speak, you yet make them feel that there are limits within which they must confine themselves. No one who has followed the progress of the ENGLISH MECHANIC for the last few months can have failed to recognise a gradual change of toue. Those whose sole object is to impart useful information feel encouraged to use your columns more and more freely; those who mistakenly, but honestly. imagine they have much useful knowledge to impart, are gradually finding their level; and lastly, those who would use your columas to "blare and bellow forth their own stupidity" are steadily discouraged. The result is, that your subscribers can turn with] confidence to your pages for sound information on a very 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 on a variety of subjects in which I take interest.

RICHARD A. PROCTOR.

LEIGH'S PLAN FOR CONVEYING RAILWAY TRAINS ACROSS THE STRAITS OF DOVER. SIR,-In the year 1861, I first conceived the idea o conveying railway trains across the Straits of Dover and took out a patent for it, connected with some other nautical matters. In the following year exhibited my patent ship in London to the Lords o the Admiralty and a number of other scientific gentle men, including Mr. Scott Russell, having been intro duced to most of them by Rear-Admiral Denman After this I sent my models to the Great Exhibitions of London in that year, and distributed hundreds lithographs with a printed description of my nex ship, showing how railway trains might be conveye across the Straits of Dover or other narrow seas.

two telescopes to one another must be at all events approximately such as to give the minimum deviation for the mean ray of the spectrum. The mode of using this instrument will be practically the same as that of employing the form depicted and described on pp. 145 and 146. Any two small achromatic telescopes will suffice for its construction, and a prism being formed of accurately-fitting pieces of plate glass cemented with gelatine (and a very little glycerine), and filled with bisulphide of carbon, will complete the whole thing. Particular care must be taken to free the edges of the glass from grease with some strong alkali, or the gelatine will not hold. The carbon bisulphide is, I think, only about half a crown a pound, and a very few ounces would fill a prism large enough for the spectroscope I am describing. Having written which I am confronted by the query of" W. R. p. 306. To him I would say, if he, 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 Browning, of 111, Minories, London, and he, for five guineas only, will supply him with the form of instrument of which a wood cut has been given in p. 145. Roscoe's Spectrum Analysis," or his "Elementary Chemistry,' published by MacMillan and Co,, London, will give Mr. Fowler has of course a perfect right to car all needful detail to enable your correspondent forth- out any scheme of his own for this object, so long with to set to work. The rest he will soon succeed he does not infringe my patent: but why he sho in doing for himself. To return, however, to Mr. go such a roundabout way to avoid this, if it can Bishop, The solutions for the observation of absorp-shown to be better than his plan, is inconceivab tion bands ordinarily recommended to beginners are except on a certain hypothesis, the nature of which Blood, Madder, Permanganate of Potash, Magenta leave my readers to infer. and Chloride of Uranium. The micro-spectroscope is more particularly adapted to this form of investigation. Iodine is the form of vapour, and (as noticed very many years ago by Sir David Brewster) the red fumes of nitrous acid gas gives strong absorption bands. I confess that the mode of making a "Solution of Sodium" does not occur to me.

A project has since been formed, I believe, by M John Fowler, for a similar scheme to mine. I wrot to Mr. Fowler, stating that although I had a paten and was the first individual to invent the plan, I ha no wish to be an obstruction, but was ready to des with him on suitable terms, or join him in the enter prise. To this letter there was no response. I wro again in January, 1867, and was informed that M Fowler was then in Italy, and that my letter wou be laid before him next month, on his return. I hea no more. On the 17th of February last, I wro again, expressing the same sentiments, but he has ne replied.

So much for the spectroscope itself. With reference to the reiterated request that I should describe the

The public are very little concerned as to who sha. have the honour of the scheme, beyond the love of f play; but they are greatly concerned about having t

Since this, Mr. Scott Russell has partly carri. this plan out in Switzerland, where a steam ferry established for conveying trains across the Lake Constance. It has also lately been partly carried o in America, by conveying trains across a broad rive

best method and accommodation. Now, if it could be, shown that Mr. Fowler's plan of shipping and unshipping the trains was better than mine, and his boat steadier, I should have nothing more to say; but I submit it is so much inferior that the public ought not to put up with the loss of time, delay, and inconvenience it would occasion. I also do not think that the plan of boat which Mr. Fowler has shown in Engineering and other publications, is the best that 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 seen, if they are ever made.

The boat (Figs. 1, 2, and 3) which I have designed for this service will not draw more than seven or eight feet water at most, with train and coal on board, if made without the pontoons ppp Fig. 3, and only about twelve feet with them. The paddle-wheels work (as shown) always in smooth water, which, by the peculiar construction of the wheels, is always kept at the outer perhiphery, so as greatly to economise the power given off by the engines. The general principles in the cellular construction 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 before. The engines are extremely light for the power given off, in consequence of the high velocity of piston traverse which the principle affords, without being too often on their centres. Steam expansion may be carried out to the utmost limit with the greatest convenience, as a very long stroke may be obtained, thereby ensuring an economy in fuel hitherto unknown in marine engines.

It will be seen from the light draught of water and the general plan of entering the harbours, that it will be quite unnecessary to change the present routes via Calais, Boulogne, or any other port, as there is a sufficient depth of water at all times. A small island marked 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 and sunk. The bottom of this shell may be made like a series of 'arches or tunrels, so that a current of water may flow to prevent the possibility of silting. On this artificial island is placed a lighthouse to guide the train boats into the harbour. The island is so placed that la boat can enter the harbour from either side with equal facility, so that the train boat, before entering from the rough sea, can 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 ensue from the desertion of Calais and Boulogne, would be avoided, as the harbours themselves may be formed on the same principle as the island in places where there is not sufficient water at present; and altogether I submit that there would be a vast saving of expense, compared with Mr. Fowler's scheme."

deck the moment the boat touches the lending stage, | as will be seen on reference to Figs. 1 and 2, and in in which a is a bridge firmly hinged to fixed supports bb on the land side, and to a floating support c on the landing stage d. The centre of the hinge is in a line 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 landing stage assume the position shown in dotted lines. There is an indent in the landing stage d, into which the bow of the boat fits. At the bottom of this indent is fixed a roller e. The bottom of the boat comes upon this roller on 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 heavy cargo. The moment the bow of the boat enters this indent it is caught and firmly held by the catches 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 and for some distance above the water line. 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 heim at each end of the ship, making stem and stern alike. These two helms 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 equilibrum 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 machinery.

DEVON AND CORNWALL. SIR,-I should like to take a walking tour along the coast of Devon and Cornwall, and there are many 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 reading hints to walking tourists, and more particularly if geological information be given, I should be glad if someone who has been in this part with stout shoes on, a walking stick in 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 MECHANIC will not fail to say a good word in favour of our friend and councillor, as they go on their holiday rambles.

SCARBOROUGH.

COCKNEY.

&c.

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 are 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 miles of Scarborough, among them is the curlew, the sea parrot, kittywakes, razor-bill, guillemotes, cirl buntings, flycatchers, &c., And as for boating and fishing 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 as glass, taking your shrimp-net, with you, and your box of specimens, enjoy a good bathe, and then after having obtained a good collection, coming back and enjoying a hearty breakfast, of hot rolls, fish, &c. Then the programme for the day is arranged, Altogether I am prepared to prove that my plan of a visit to the Old Castle, built in the reign of Stephen, boat will be much swifter, steadier, safer, and cost by the Earl of Albermale; the walls of the ruin, 9ft. no more than an ordinary boat with outside pad- thick; and then standing on such a bold promontory, dles. I calculate the passage will occupy only fifty 300ft. above the level of the sea, the rocks direct minutes in fair weather. I also contend that my beneath you, and here we sit down and rest awhile, plan of entering the harbour, shipping and unship-watching the Naval Reserve men or the Artillery ping trains, will be more efficient, and cost less than firing at the target that is anchored off. Then there the method shown by Mr. Fowler; but of this I leave is Oliver's Mount, 500ft. high, and one mile from the the public to judge.

EVAN LEIGH, F.S.A., Manchester.
TOURISTS' TRIPS.
SCOTLAND.

SIR, I was much pleased to see Mr. F. Harwood's letters on "Tours in Ireland." A friend and myself are

town. We get to the top without any difficulty, and then what a sight breaks on our astonished gaze. Away! away!-as far as the eye can stretch, the waves and the sky seems to touch.

I think I hear some of your readers say, "Oh, yes, this is all very nice, but what a long purse you require for those pleasures." To this say, "No, not so much as you spend over your pipe or beer; it is

within the reach of every working man, this lifegiving, soul-renovating enjoyment. The railway xpenses by the excursion trains are very low indeed, and the most comfortable lodgings, within three minutes' walk of the sands, can be obtained for the low charge of one shilling a day-that is for bed and use of sitting-room, and cooking and victuals-one shilling clears all; the charge for boarding and lodgings at the hotels is from 68. 6d. per day. Should any of your readers want any more information I should be most happy to render it.

W. W. LARKIN, Scarborough.

SIR,-1 am going "to do and exercise" as the lawyers say, the Englishman's grand privilege, in fact the privilege of all British subjects, the mainstay of our institutions, &c., ad lib.-that is, to grumble. My cause of complaint is this, your paper is too scientific for the time of year. "All work and no play 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 nature than many of the voluminous essays that are inflicted on us" poor cusses." 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 the inclination to travel that "side of Jordan." You possess, I suppose, readers in every town of the kingdom; well, let one who is capable of doing so in each town, send you a short note of the ancient buildings, &c., that the town possesses, that are worthy of a visit, 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 over plus, 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 places there are around it. There is Kensington, for example, with its Palace, Lord Holland's Park, &c., while Twickenham, and all up the river, bring recollections to mind of Horace Walpole, Pope, Sheridan, Fox, Burke, &c. Not only would these notes possess a passing interest, but if carefully written and unnecessary verbiage dispensed with, they would possess a lasting value, and, like a thing of beauty, be a joy for ever. If any of our sternly scientific correspondents like to treat the subject in a purely practical manner they might do so with great gain to themselves and their readers. For instance, there is Willesden cage, whence, so tradition sayeth, that noble hero Jack Shepherd escaped (by the way, what a striking picture this would have made for the Police News!). Well, that could be treated of in a purely scientific manner, and we might have stated for the benefit of posterity the actual time the hero took to accomplish his feat-in fact, the number of, square inches of brick, wood, &c., disturbed, and a calculation of the power of the leverage employed would be very interesting. But let us have no Beardsleyism. Human Science is all very well in the winter, but in the summer let us have the Science of Nature and the mathematics of green fields, rippling, waters, and all those other sights and sounds which speak even to the hearts of the most ignorant of Him who clotheth the lily and careth for the sparrow.

A LONDON SUBSCRIBER. "A Londou 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 the cultivation of what he calls "Summer Science," by writing on some of the interesting objects in and about London.-Ed. E. M.]

GEOLOGY.

SIR,-I am glad to know that we are going to have a course of letters upon geology. I have travelled in some of the high and lowlands 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 in any of those places to which I have referred.

I don't know anything more interesting and instructing than that of sitting at the mouth of a coal-pit (which the miners are newly sinking), and watching and examining the materials that are brought from below-say 200ft. or 300ft. 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 water mark, from which numerous fragments of fossils are washed up by the action of the sea, which I have often picked up.

VERITAS.

LOW-WATER DETECTOR AND SAFETY
VALVE.

SIR,-I extract the following account of an ingenious device combining a low-water detector, alarm, and safety valve, from the Scientific American:-The safety valve is made as shown in section at A, with a flat naular face, its 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 B, and into the upper part the inclined pipe C, having at its outer end the hollow sphere D. The sphere D has a pet cock at the top to allow the efflux of air when the valve is first adjusted to work. On the opposite side of the valve A from the pipe C projects a bent arm E, pivoted at F, and carrying a weight by which the valve can be adjusted to the required pressure. The pipe B descends below the normal water-level, as shown.

In adjusting this valve the pet cock in the sphere D is opened when the air escapes, and the pressure of the steam upon the surface of the water in the boiler causes the water to rise and fill the cavity. The weight upon the arm E is then set to counterpoise the weight of the water to the pressure it is desired to

LOW WATER DETECTOR AND SAFETY VALVE. maintain. Any pressure exceeding the required pres-, sure raises the valve and relieves the boiler. It will be also evident that as soon as the water falls below the pipe B, steam will take the place of water in the pipe C and the sphere D, and the 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, and a very wide opering being made the discharge of steam will be so copious as to be readily distinguished from the smaller escape due to pressure alone.

P. HUMPHREY.

cast iron, in one piece, bearing 3 short legs to stand on, and a fin. ball in centre screwed; B barrel of pump, G handle of piston and piston rod, D small cock to equalise pressure where required, also to allow of vapour or liquids or of gases to enter the receiver when exhausted. I use a disc of very thin vulcanised rubber between pump, coil, and receiver, they requiring no luting of any kind to keep them tight, which is of great importance; there are 2 valves E E. What I use is thin vulcanised rubber, or oiled silk will do. Fig. 3 is an enlarged section of valves; the rubber or silk is held upon the aperture with a silk thread

But

wound round the 2 ends of rubber when folded over it; the piston rod is made of brass tube; the under end carries the top valve, the other fixed in bottom of pump; the piston is made with 2 cup leathers, back to back, about 1in. depth. As to the vacuum this pump can force, I attached the tube Fig. 2 to plate of pump after a 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 14in. The vacuum is such as to produce Gassiot's Fountain in a satisfactory way. let me here remark that although this sample pump works very well, I know that there are others that are far superior to it if the cost be no objection. But here it might be as well to state size of coil and battery employed in producing those experiments. The coil contained fully 5lb No. 28 of secondary copper wire; a Grove battery, the platina plate 3 by spark in free air fin.; the coil has no insulation, but the cotton covering with a coat of shellac over all, but is wound by beginning at one side of bobbin, which is glass, and filling the under corner first, then up and down till the whole length is filled, thus 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 given last week by "Inductorium," it must be far superior to mine if length of spark without reference to thickness is to decide the point. Having thus far endeavoured to help a brohter I trust in Inductorum" fulfilling his promise, so that I may lengthen my spark.

in.

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 Rhumkorff from him, and I feel hopeful and trustful of hearing soon from him or some one upon this point. it having an important action in the working of all coils.

PHRENOLOGY.

A. FARQUHAR.

SIK,-In reading over the communication I sent and which you have inserted in the MECHANIC, I was much amused by finding lump substituted for bump. I think it must have produced a smile on the countenances of 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 too much to expect, for the following reasons:The preacher might have a phrenological development so varied and comprehensive that he might have made a good engineer or successful merceant, or a clever statesman, or a 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 a blacksmith, one a joiner, another a painter, and so on, and ask a phrenologist to decide what they all were. A phrenologist would tell on examination whether the person examined; had the necessary organisation and deve

"W. A.,

tion in your pages, I shall be glad to oblige and perhaps others, and show my estimation of the pages of the ENGLISH MECHANIC, by forwarding one. I agree with "W. A.," in thinking that an immense field is open for the introduction and practice of medical galvanism, and once break down the at present, impenetrable barrier of medical opposition and prejudice, and open the eyes of the profession to the 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 stand as a recognised household and popular remedy, but as matters now are, a large proportion of the faculty, whenever they find it in use in a family on which they call in their professional capacity, invariably set their faces against it--in the majority of cases without ever having given it a trial, even in a case of a patient most susceptible to its influence and if they do not positively demand the discontinuance of its use, they as invariably give their opinion-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 I know has been the verdict in several cases where I have had the pleasure of bringing the patient back to robust health. by the almost surreptitious use of a properly applied current, the physician in the meanwhile chuckling over his supposed cure. I cannot allow these few lines to come to a close, without that medical stating my firm belief and conviction alvanism, united in its proper proportion with the use of proper medicine, is yet destined to be the means of effecting cures which are now either impossible or are of a protracted nature. I shall be glad, Sir, if this letter may have the effect of evoking replies pro and 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.

SIR,-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 contined to my room through a severe accident-it occurred to me that I could do worse than employ the weary hours of my convalescence in (to the best of my ability) instructing my fellow-readers who desire to pursue this interesting branch of science how 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. Having satisfied ourselves that one theory of the healing art is right, we unhesitatingly conclude that every other must be wrong. Having found the system adopted by one set of theorists succeed in certain cases, we condemn every other system.

In this, it appears to me, we are wrong. me to be the business of an inquiring mind not only It seems to ta invent theories, but especially to gather facts wherever they may be found; to accept truth, from whatever source it may be presented. Results, as far as they can be ascertained, should be carefully marked and studied. Special conditions should be industriously noted and observed; and from such material theories should be patiently built up.

These remarks apply in a more forcible manner to the healing art than 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, the habits, and the physical conditions of patients are so various, that it 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 homeopath. And yet, after all the gin and porridge of the sick nurse-the gruel and nitre of the allopath-the drop of camphor of the homeopath-the wet sheet of the hydropath-the composition powder of the Coffinite-the vapour-bath of the herbalist-and the pint-and-a-half of cold water of the teetotaller, how few but what seem to run their course; and how few, with but little care at first, quietly subside! How sometimes, with all our care, they hang about for months; and how again, when sometimes let alone, they seem to die the quicker. Yet who would despise the hot footbath advised by all, or say 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 disease is better understood, the healing art will have made a large advance. Whatever may be the true system of medicine, If such has yet been discovered, we know that nearly all chemical processes are more or less under the control of electricity or galvanism. Chemical force, as Faraday, in his " Physical Forces," beautifully demonstrates, is convertible into galvanic and magnétic 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 into, 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 in the body may be guaged by means of a delicate galvanie pile. Determinable galvanic currents are continually being generated by the chemical processes carried ou in the animal economy. Electric currents are constantly circulating throughout the nervous system. The galvanic current is found to possess a specific power over many of the most important fauctions and secretions of the body. Every throb of the brain, every pulsation of the heart, every twitter of the nerves, is productive of, or connected with, electric

excitation. Dr. Reymond has conclusively demonstrated that the muscles and 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 the state of health or disease of the bodily subject and 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 disease, 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 be set up, and a current of great intensity and quantity is requisite. In nearly all cases galvanism may be applied as a remedial agent without the slightest inconvenience or pain, and is often most successfully used when scarcely perceptible by the 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 galvanic force will, in ninety-nine cases out of a hundred, be found useless; and such appliances as galvanic belts and chains, which give off but small quantities of galvanic force of very great intensity, in the two former classes of disease, as I have often seen, are liable to become positively mischievous in their effects, though they may occasionally prove beneficial in cases of effusion of matter into the joints, in rheumatism, and similar 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 current to the strongest of which the machine is capable. He should also be 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 korff's, or similar coil, capable of giving the strongest tube and water arrangement, and the other a Rhumsecondary effects. Some arrangement should also be provided whereby the whole of the cells can have all their positive poles united and attached to one end of the coil, or) terminal wire, and all their negative poles brought together and united with the other wire, instead of being alternated in the usual manner, so as to afford the greatest quantitative effects. Zinc and silver or platinum plates should also be secured, of different sizes, and with insulated knobs, to take the place of the handles, for its more ready application to various parts and organs. It will often be found better, in local application, for the operator to allow the current first to pass through his own body, and then with the moistened knuckles of his free hand to gently rub the affected parts. This mode of application, while more efficacious in some affections, greatly melit in several other respects. lows the intensity of the current, and appears to modify

forms of disease.

Electricity and galvanism used in this way, and cum grano salis, will be 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 case it 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 other 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.

EDMUND M. T. TYDEMAN, 10, High-street,
Brighton,

EMIGRATION.

SIR-In your last issue but one of the ENGLISH MECHANIC I observed, under the head of " Answers to Correspondents," a request that Mr. Rogers would communicate intelligence in connection with emigration to the Western States of America; and as 1 have not observed any correspondence from a namesake, and having supplied something trifling on the 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 some friends there monthly; and anything I 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 use to him if he went out; has been educated, and practised for a short time, as a solicitor; has been engaged in farming for some years; could command £1000 to purchase land, &c. He wished to know whether I would recommend him to go to Canada, either Upper or Lower, and from my experience (two years' travelling) of that country, I said certainly not. It is a miserable place-winter too long, all people badly paid, and rich people are not numerous. Most of those who have a little money have earned it so hard, that I have known some who would not trust the best banks in Canada with it, but keep it locked up or hidden in their homes. These are 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 in Kentucky (one of the middle States), he replied that the amount of money in that State would be a small thing, the profession was overrun, land very high in price; but the State of Kentucky was one of the best of the middle States. In Nebraska the land is cheap, rich, and yields abundantly. A friend there says he grew beets in his garden, last summer, that would fill a nail keg (a vessel as large as a butter firkin), and that everything grows so in proportion. Wild fruits grow in abundance, and a tremendous emigration is growing on. It is a new State. The capital has recently been removed to Lincoln. An English colony, with which one of our leading members of Parliament is connected, is located near the abovenamed place. The public buildings are now being built. Minnesota is a beautiful State, but cold in winter for any one who likes a warm climate.

Middle Tennessee offers many inducements, but is full of Confederate soldiers. A large number of Swiss are settling there. For a man who has a taste for farming, Nebraska in every respect is good. There are a good many tribes of Indians still in this State, who sometimes give some trouble; but they are not so fierce as they were some years ago. However, a border life has its drawbacks as well as its benefits. Land in Nebraska can be bought for from £3 to £6 per acre within about 15 to 20 miles from the splendid city of Omaha. A person buying land should become a naturalised citizen to enable him to hold land in the United States or to practice a profession in courts. Anyone going to any of these States must not expect to find society in the same condition as it is in these old countries, and should go prepared for such change. Sons and daughters must work in and out of doors for some time until they are in a position to hire help. They must milk, feed stock, learn to mow, sow, and reap. Although society is not all first-class, still there are very many first-class people to be found there, especially in the older places. most of the Western States, and are more peculiarly These remarks apply to adapted for those intended to settle on farms, and who have some capital.

Being pressed for time, I must conclude.

S. ROGERS.

correspondents in your last two numbers, upon the SIR, I have just seen the lucubrations of several subject of emigration. Knowing your large circulation compels you to go to press at an early moment, I let your readers, and especially those intending to have determined to write a few lines off-hand. Pray emigrate, beware of the fanciful ideas which may be mooted, and which would prove every square mile under the sun the most suitable for emigrants to occolonies possessed by England offer the best spheres cupy. I believe, yes, thoroughly believe, that the to our superabundant population.

The tirade of "E. W. J." about paying for fancied security is all moonshine; lawless desperadoes go about without let or hindrance you are likely to pay much more in the "countries of the southern main" for no security at all. Bands of in many parts of South America, seeking whom they known, that every man looks out for himself. "J. G.'s" may devour. The puerility of the authorities is so well description of the Argentine and River Plate territory is not to me very pleasing. I do not see how a mau would better himself by settling there. But suppose such to be the case, what are his prospects? No roads whereby his superabundant produce may be utilised and money gained. Hunting accoutrements and Guacho life seem best adapted to the territory. The choosing a spot by a navigable river, at least for canoes, is easier said than done. Thus, as J. D. Rogers this I mean the United States. Some of his remarks I so excellently describes, we must turn to America; by protest against--viz., those directed against the English Colonies. Australia is not too distant, neither is New Zealand, Natal, or the Cape-countries possessing a climate as equitable and salubrious as any part of the United States. Then, again, we have Columbia, by no Here, then, is enough land to absorb the whole popumeans an insiguiffcant part of the British Empire. lation of the "British Isles," if need be. I admire the energy and self-dependence of the working men at Mile-end, and have no doubt that they will thrive at their new home. But I question if they will find the laws better. Certainly if our Legislature was to take more interest in colonial matters very much more good would be the result. Apathetic, careless, ignorant, to sion, and even then the least possible work, ignoring a surprising degree; doing nothing but under compulthe claims of our superabundant population; wasting time in useless squabbling-are a few of the remarks hurled against our Legislature. How true, may be known by consulting an article on Englaud and her Colonies by J. A. Froude, in Fraser's for January. I believe Mr. Froude would have no objection to the republication of his article in the columns of the ENGLISH MECHANIC, and if this could be done a great boon would be given to its readers. One 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.

covering the hopelessness of the struggle with capital, Are we to wait till our own artisans, disand exasperated by hunger and 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-quarters of the English nation! If Mr. Gladstone and Mr, Odger are indifferent, we appeal to Mr. Disraeli. This is one of those imperial concerns which the aristocracy, lifted by fortune above the temptations and necessities of trade, can best afford to weigh with impartiality, &c."

He evidently thoroughly believes in a national system of emigration, in which Government vessels conduct the wayfarer, and Government arms encircle and sustain him till the time has come when he can sustain himself. Of course Government would be no loser in the long run; the first expenditure would easily be recouped by various means which, however, I cannot at present discuss. I Again wish prosperity to the noble workers at Mile-end, a speedy and auspicious departure, and a successful issue in their new sphere!

WHEEL TEETH.

F.R.G.S.

SIR,-In answering a query on the above subject, I had occasion to speak of the Manchester wheel gauge, and attempted to describe it; I now forward for engraving, if you please, what I use in place of the gauge as ordinarily made. As this last is expensive, costing 128. for about sixteen rows, divided on box wood, and some more for the smaller ones on a brass plate. To use it, say, to ascertain the gauge of any wheel you already have, count the teeth, and place the wheel flat on the gauge where you find the diameter of the wheel covers the same number of equal parts on the scale, as the wheel has teeth. And that line of equal parts is the gauge to work to for any other