342

favourable circumstances there is reason to hope that it might be accomplished in less than forty.

I do not know why the Messrs. Seaward should regard the proposed new passage with an evil eye. There is room enough, and to spare, for both projects; and it is certainly rather a disgrace to us that steam navigation by the Cape has not yet been effected to any extentthat the voyage of the Enterprise should yet remain a solitary instance of the spirit of "enterprise" in that direction. Let Messrs. Seaward persevere, then ; but let them not seek success by detracting from the merits—totally distinct as they are of the "south-east passage."

There seems to be still a little misconception in your pages as to the purport of the recommendation of the Parliamentary Committee. They considered the practicability of the route by the Red Sea as already demonstrated, and recommended the immediate establishment of a regular line of packets on it, the expense to be divided between the Government at home and the East India Company; and the 20,000l. voted is to be appropriated solely to making the experiment of a voyage by the Persian Gulf and the Euphrates.

I remain, Sir, Yours respectfully,

F. H.

grooved wheel at the bottom of the plane; or, instead of a large wheel at bottom, a half circle of grooved pulley wheels carry the chain round at bottom. The chains of course are endless ones. The loaded carriages invariably go down the same side (as the machinery moves invariably the same way), and the back carriages, or empty ones, return by the other side of the chain. The carriages are taken off empty at the top of the plane on one side, and put on loaded on the other side of the chain, one at a time, so that a regular distance between each carriage on the chain is always attended to. The same is done at the bottom, that is, when a loaded one is taken off, one loaded with back carriage, or an empty one, is put on the other side of the chain.

There are generally three or four carriages on each side of the chain, at regular distances from each other, going down and returning; and when the chain breaks, the whole of the carriages, chain and all, go down the plane in a confused heap. Nor is this all, for the chain itself being knocked about is often cracked and damaged, so that other breakages generally follow; and after repeated breakings of the chain, the iron becomes greatly impaired in tenacity. (Here I beg leave to say, that

London, August 15, 1834.

1.

PRACTICAL REMARKS ON WORKING
INCLINED PLANES.

Sir,-The plan adopted, in the Wemyss colliery, to stop the carriages on the inclined planes when the chains break, answers the purpose, no doubt, very well in underground situations, as observed by Mr. Landale; but the inclined planes in this district are mostly employed for sending weights down the hill-sides to the canals, tram-roads, &c., at the foot of them. The machinery made use of consists of nothing more than a horizontal wheel (some of them incline towards the planes) at the top of the plane, with a groove round it for the chain to run in, and a break to govern the speed; the chain running round the back of another

the best way, I think, to restore the iron to its quality again, is to draw it through a fire and heat it well: by so doing, any flaw or crack in the links may be discovered.)

The only way that I have thought of as likely to stop the carriages on an inclined plane, working on the above principle, when the chains break, is this:We hang the carriages to the inclined chain by bridles-chains in the form of fig. 1. A is hooked upon the endless chain; the hooks B and C are hooked on each side of the back part of the carriages. Now, if there were a toothed rail laid (see fig. 2) as near the middle of the road, on the planes, as the rollers and the traversing of the main chain would allow, I think it likely that the double of the bridles at D would catch the tooth-rail at E; and as it is necessary for every carriage to have a bridle attached to it, both going down the plane and returning, I think several of these bridles may take hold of the toothed rail, and stop the whole from going down the planes the bridle chains may be made strong for the purpose. The only inconvenience in that would be that they would be more cumbersome to handle.

Mr. Landale's plan, fig. 4, No. 569, Mechanics' Magazine, is something on the above principle; but to catch the carriages by the bridles as above described, would not produce any alteration in our present mode of working. The only additional expense would be the laying of the toothed rail on the inclined planes.

I admit that the sudden jerk, when a bridle first catches the toothed rail, may break that bridle chain, but the jerk would be less on the next taking hold, for the double of the bridle chains would be trailing over the tooth-rail until they all took hold.

I am, your obliged servant,
THOS. DEAKIN.

Blaenavon, August 6, 1834.

A FEW MORE WORDS IN BEHALF OF MATHEMATICAL SCIENCE.

Sir,-As I find I must be absent from London for two or three weeks, I will not have an opportunity, during that time, of continuing my appeal in behalf

343

of mathematical science; and as my last short article will hardly be a mouthful for your highly-gifted correspondent, Mr. Cheverton, I beg leave to give him one morsel more before I take my departure.

LEWIS FREND.

St. John's Wood, Aug. 17, 1834,

In the first place, I must correct on error in my last. In speaking of John Dollond, page 331, col. 1, line 3, instead of 1740 or 1741, I should have said 1753.

Notwithstanding the opinion expressed by Sir I. Newton on the effects of refrangibility on the refracting telescope, Euler, it appears (although a rigid disciple of the Newtonian philosophy), was not satisfied; for we find that, in 1747, he tried to prove the possibility of destroying the effects of colours on the focal image, by imitating the structure of the eye, which he considered to be the most perfect of all optical instruments.* He proposed to construct a convex lens, having its cavity filled with water, from which he expected to produce distinct vision freed from the effects of refrangibility, and also from the aberration produced by the spherical figure of the lens. He, however, did not altogether succeed —in all probability for the same cause that Gregory failed. In truth, he was not a practical optician; pure intellect was the region of all his speculations. In 1752, Mr. John Dollond communicated to the Royal Society of London, a paper endeavouring to show that the principles advanced by Euler were quite at variance with those deduced from Sir I. Newton's experiments on the refrangibility of light; although, at the same time, it was doubtful if either the one or the other of their theories were consonant with the laws of nature. On this subject the scientific world were much divided in their opinions. At last Mr. Dollond, in order to satisfy himself, had recourse to experiments, the result of which was, that he found that he was wrong himself, and that Euler was right. Being thus cured of his former preju

I do not know what Euler's opinion on this head might have been 19 years afterwards, when, unfortunately for himself and for science, he became totally blind.

344

dices, although not liking the expedient of enclosing water in the lens, he at last, after four or five years of fatiguing research, succeeded in constructing an achromatic refracting telescope, in the way mentioned in my first article. And here, Mr. Editor, I cannot help thinking that although Euler did not succeed, still the discoveries he made as to the method of destroying the errors arising from the effects of colours on the extremities of the focal image, were the means of directing Mr. Dollond in his construction of the first refracting telescope, which he produced in the year 1757. However, be that as it may, he was more fortunate than Mr. James Gregory; he lived to see, and was one of the first to congratulate Mr. Dollond on his great achievement. He was too much of a sage to indulge in any peevish reflections on this seeming triumph of Mr. Dollond. Different was the fate of Mr. James Gregory; he did not live to see a construction of his reflector, according to his own principles, although Newton with his own hands had attempted it. However, in 1724, Mr. James Short, a first-rate artist, and highly celebrated for his mathematical and astronomical attainments, succeeded in constructing a telescope according to the principles of the first inventor.

What Mr. Cheverton means when he says, that the most valuable method of determining the longitude is by means of the telescopes constructed upon the principles of Mr. Dollond, I am at a loss to guess. Does he mean that of finding the longitude at sea ?* If so, I am conpelled to inform him that he knows nothing about the matter. Hadley's reflecting quadrant and sectant, as improved by Ramsden's dividing engine, must rank as one of the greatest mechanical discoveries that ever was made in aid of nautical (or, I might add, practical) astronomy. It is now universally used at sea for determining the longitude. While mentioning the names of Dollond, Short, Hadley, and Ramsden, those of Graham and Bird ought not to be forgotten; they equally distinguished themselves in their various mechanical and optical discoveries. The only charge that can be

The writer of this article has had considerable practice both at sea and land, in taking and working Innar observations,

Sir,-In answer to the inquiries of J. L., inserted in the Mechanics' Magazine for June 7, No. 505, I beg leave to state, that any glazier will cut a glass plate circular, or nearly so; the edges may then be finished in a lathe, by cementing it on a chuck, and applying emery and water on a piece of tin-plate, in the manner the watch-glasses are finished. The hole in the centre may then be expeditiously cut while in the lathe, by cementing a small block of wood to the centre of the plate, about two inches diameter, and half an inch thick; in the centre of which turn out a hole, down to the glass, of the size required. J. L. must then get a copper ferrule, of the same size as the hole in the wood, and about one inch and a half long; half of this ferrule must be fixed on the end of a tool handle, for the convenience of holding it steady in the hole previously made in the wood on the glass. If the copper ferrule or tube is properly applied to the centre of the glass with emery and water, it will very soon cut out from the centre a piece the size of the copper tube. J. L.'s glass will be thin enough for his purpose, and of sufficient diameter to do all that he

requires. He may easily fix the plate on its axis, by having a shoulder of a piece of boxwood on the spindle, and another piece to screw firmly up against the plate this will keep it from turning when in use.

Optical glasses are ground with emery, of various degrees of fineness, on brass tools; the very small magnifiers are best

!

*

"

Ballad of Rosabelle-Sir Walter Scott's Lay of the Last Minstrel.

Magdalen College, Cambridge,
August 21, 1834.

Sir, In reply to your letter I send you, copied from my papers, the rigor. ous enunciation of the theorem in submarine operations, the rationale of which I gave you in one of our late conversations when I was in London, as a witness before the Committee of the House of Commons for the Improvement of the Navigation of the Shannon and its tributaries.

Suppose a perfectly solid rock under the sea, and either a natural cavern or artificial chamber to be formed in it, with a horizontal orifice, sufficiently wide to permit a man to pass through it. I speak of a depth, not like that of the hall of Domdaniel, where the magicians, destroyed by Thalaba, had their col lege, and their, self-suspended spherical

345 go down into the natural or artificialib chamber in the rock, and remain in it quite 10 alone, after the bell in which he des scended, and the companions who dessa scended with him, shall have been taken o out of the water altogether. Whiles there, he may either read or write, or d make drawings, or occupy himself with d a musical instrument, or in any othera similar manner he may choose-quite un. wet, and in his ordinary costume, without alteration whatever by candle light, or by lamp light, burning withins the chamber. He shall be suspended into the air within this submarine and sub4008 terranean chamber-to him (to take a description from Ossian) an airy hall' -and he shall hold conversation with a person above, utterly unsupported by: land or by water, or a vessel on the water, but held, like himself, in suspension in the air.

any

They may not only hold conversation, and interchange writings or drawings a with each other, but they may even ex-me change places-or both may be together, d either under the sea or above its surface, held in suspension in the air.

66

Finally, either one, or both, or three, &c., (the number of persons forms no element of the abstract mechanical principle, and I am now only speaking of an ABSTRACT PRINCIPLE)-I say that either one, or both, or three, &c., after having been either held in suspension in the cavern, or in the chamber under the sea, or standing or sitting in it, on the having been held in suspension for an bare rock itself, may ascend; and after indefinite time in the open air above, they wish it, and soar away in the may be taken into the car of a balloon,

do

usual manner.

grob act "Remember, I am giving a mere ab-ser stract theory,but unless the laws of H hydrostatics and pneumatics, and the bes general laws of nature, have altered op within the last five minutes, the opposite process will hold good too; and they may 2911 be transferred from the car of a balloon to the point of suspension in the air, and may then descend into the submarine w