In the earliest condition of man-savage man I mean-the food most nearly assimilating to him was the flesh of the lower animals. But for this provision of nature-this natural elimination of food fitted to his wants-he must, in common with many of the lower animals, have disappeared from the earth almost as soon as created. He could scarcely have subsisted on roots, at least in cold climates; and a long time intervened ere his inventive powers converted peculiar grasses into wheat, oats, rye, barley, and other grains; and though the lower animals are still used as food, invention has been constantly at work to vary their physical qualities, making them, by art, still more fit for man's purposes. As intellect shall continue to make progress, new discoveries in chemistry will continue to devise new means of procuring food, and at length enable us to put an end to the coarse —and, to the delicate imagination—the humiliating process of entombing the dead bodies of the lower animals in our own persons. So far from advocating abstinence from animal food, I consider it the best we have in our present limited state of knowledge; and as an essential ingredient in human progress, yet, still only a temporary ingredient. Knowledge will eventually be ours to prepare food from inorganic matter, as stimulating and as nutritious as that now furnished by the lower animals, who are made to die, that we may live.

In man's earlier time, his fuel was wood; but, as population thickened, wood lessened in quantity, and nature's next provision was laid bare to his view. Coal was the fuel suited to his improved condition, when his knowledge was sufficient to devise means of raising it from its subterranean store-houses. He first consumed the upper strata, and his knowledge became enlarged to penetrate to still deeper stores. Through the instrumentality of coal, have the modern wonders of locomotion been achieved. But coal is a constantly-decreasing quantity not reproduced by nature; already may we calculate on a not very distant period when it will cease to exist. But, ere that period shall have arrived, man's constantly progressing knowledge will have devised means of extracting heat by chemical agencies, as superior to coal as coal is to wood.

In like manner, nature seems to have

provided trees for us, for the purpose of ship-building-fitted for the slow progress hitherto attained, but of too slow growth for our increased activity of locomotion. The thickening of the population in England cannot afford forest space; and the ample stores of iron, useless, in former times, from want of the knowledge necessary to render them available, are now more valuable than the organic matter of the forests.

Several iron steam-boats have been sent to India for river use, built in London. Many are in use on the Clyde, plying between Glasgow and Greenock; and the first trial of a sea-going iron vessel is now about to be made between Glasgow and Liverpool. It is also the largest yet built, being of five hundred tons measurement; and the form is well proportioned. The builders expect to get from 12 to 15 knots speed out of her.

As befals most novel plans, prognostics are rife, that it is impossible to bring iron steam-ships into general use, especially for the sea. The reasons alleged are as follows:

First, The liability of iron to rust, and the consequent quick destruction of the

vessel.

Secondly, The danger of breaking large holes in them when striking against obstacles.

Thirdly, Their liability to leak, from the vibration of the engine.

Fourthly, The alleged impracticability of navigating them across the ocean, owing to their effect on the comp as .

An answer to the first objection, viz. rust, may be found in the galvanic process by means of zinc-thus rendering the iron indestructible by ordinary oxydation.

The second objection is an unsound one; for an iron vessel striking against an obstacle would merely dinge in, and rebound; while the wooden one would be cut through, and the planks started with an equivalent shock.

The third objection-the liability to leak, from the vibration of the engineis of more importance. But this objection may also be made to wooden vessels. It is true that wood may swell, and diminish the effect of a leak, which

*Our esteemed correspondent appears to have overlooked the Rainbow, now trading between Antwerp and London, a notice of the performances of which appears in another part of our Number. ED. M. M.

construct them of wood. The specific strength of the material limits the size of construction; but not so with iron. The strength of iron may be increased to any amount, i. e. the size of the component parts.

Be

The third requisite is economy. The economy of the iron construction has been already alluded to; but increased size and increased speed are still more fruitful sources of economy-being an economy of expenditure, far more important than economy of outlay. A large number of passengers can be carried at a far cheaper rate than a small number; and steam can also be used with a less proportionate waste in large engines, than it can in small ones. yond all this, there is the saving of time, involving expensive maintenance and much wear and tear. A passenger would rather pay his thirty guineas for a five days' trip, than for one of twelve days; and the actual maximum of speed for ocean steamers being yet far from ascertained, owing to the expense of the experiments on the large scale, we cannot yet prescribe a limit. One thing, however, has been satisfactorily ascertained that the largest vessels have proved the swiftest; and this seems to indicate the true principle, which has yet to be worked out.

In the science of water locomotion by by steam, one most important principle seems to have been wholly overlooked, the necessity of getting rid of all undue vibration, in order to attain the maximum of speed. It is well known that a vessel which is too "crank" or rigid, will not sail well. She will not yield to the motion of the water and thus produces a partial concussion. The American schooners belonging to Baltimore carry the heavy sails in their long span by its own elastic strength, with scarce any aid from shrouds, and the heavy yards of the Mediteranean feluccas have the same elasticity. If a Baltimore schooner be tightly stayed up with rigging its wondrous speed will depart from it, and it will be as a common vessel. This fact was once proved by our dockyard wise-acres at Portsmouth, who thought to make the vessel more seaworthy by trummelling her up in a multifarious tracery of ropes. The French privateers during the war understood the advantage of elastic yielding, when

by knocking out the wedges from their beams they were enabled to gain extra speed and escape their swift-heeled adversaries.

I once in your pages advocated the plan of applying springs between the axes and circumferences of paddle-wheels; my reason for this was, that I had noticed the mischievous vibration caused by the strokes of the paddle-blades on the surface of the water, causing annoyance to the passengers and retardation to the vessel.

I have since thought more deeply on the subject, and am satisfied, that the principle of making the framings of the engine a fixture of the vessel's hull is altogether wrong. The vessel itself should resemble a fish-not a dead fish but a living one-not a loose mass falling inertly from one form to another-but a well-proportioned body, with an elastic power of yielding to pressure within certain limits. and of acquiring its true form by virtue of its elasticity the moment the pressure is removed. This is the reason why boats without decks sail better than boats with decks. This is the reason why Thames wherries and Deal gigs are the fastest rowing boats in the world. Large vessels made of sheet iron, if properly constructed, with the rivet hands flush and smooth, are better adapted for this elastic yielding and smooth gliding motion than any other construction.

When a Thames waterman rows a wherry he does not keep his body rigid, but sways it to and fro, according to the motion, and he is careful to enter his oar in the water with as little shock as possible. Were the waterman tied fast to the thwarts, with his limbs rigid and prevented from feathering his oars, the result would be a great decrease of speed.

In a steam-vessel the engine is the rower, improperly fastened to the hull, and transmitting to it every shock and concussion, annoying the passengers and mpairing the speed. The true method of construction would be to frame the engine separately, and then to attach it to the hull of the vessel by the intervention of springs or elastic substances. By this means the motion of the vessel would not be unduly retarded, and the power of the engine would be confined to the axis and wheels.

It is, I believe, a known fact, that a boat can be "sculled" with a single oar astern faster than she can be rowed. The principle of sculling is that of forcing a wedge down an inclined plane alternating from side to side. On this principle is constructed the stern sculler patented by Mr. Taylor. Instead of the shaft athwart ship to which paddlewheels are attached, he uses a longitudinal shaft passing through a stuffing-box into an opening formed between the stern post and the dead wood. At right angles with this shaft is placed a kind of oar blade working in the opening with a continuous revolution. Being set at an angle with the plane of its revolution, this blade is continually cutting against an inclined plane, and thus the vessel is forced onwards.

The experiments exhibited with this simple instrument were as follows:

:

A model boat proportioned to one of the best government steamers was set moving, by a clock-spring power in a trough of water about 30 feet long.

The spring being wound up to its full power, the boat made the distance in fifty seconds. This was repeated more than once with a very trifling variation.

The paddle-wheels being removed, the sculler was applied, and the distance was accomplished in thirty seconds. A repetition of the experiment gave the same result, and there was no apparent reason to question the perfect fairness of the experiment.

There are two reasons to account for the superiority of the sculler over the paddles. First, that the sculler always works in unbroken water, whereas, the paddles frequently act against mere froth, churned by themselves. Secondly, the sculler acts in deeper, and therefore denser water, always immersed, without any load to lift at the return stroke; whereas, the paddles work in surface water varying their immersion with the roll of the vessel, and lifting a load as they emerge.

The objects I advocate for the purpurse of challenging discussion in your pages may be thus summed up:

First, The use of iron steamers for ocean navigation.

Secondly, An increase of size till the maxiinum of speed be attained.

Thirdly, Hollow air-tight decks, and a divided hold, to ensure safety.

39

CIRCULAR BOILERS AND CYLINDRICAL FLUES.

Sir,-The remarks of A. Trevelyan, in your Number of to-day, seem calculated to prejudice the public against all circular boilers, which are, perhaps, the safest as to form that can be made. The accident they are most liable to is, the collapse of the circular flue by pressure on the outside. The danger is in the flue, not in the boiler; and many have no internal flue.

"A public demonstration of dislike to cylindrical boilers," would be a public demonstration of gross and most unwarrantable prejudice.

Cylindrical boilers are not more likely to be used to generate steam of a greater pressure than they were intended to bear, than other boilers are.

I am, Sir, yours, &c.

Oct. 13, 1838.

C. G. JARVIS.

DEANE'S IMPROVED DOUBLE-ACTION LEVERED LOCK.

Sir-To put a thing under lock and key is, unhappily, not at all times to make it secure. For all people know, sufficiently well, that it is not love alone which laughs at locksmiths. To find out any contrivance which may render assurance doubly, or even singly sure, is what has long been desired by those who have treasures to take care of, or secrets to conceal.

Intricacy in the structure of the lock has been considered the grand secret of success; and makers have multiplied grooves and wards to a great extent, but not to the complete satisfaction of minds only moderately suspicious.

In the figure it will be seen, that the bolt A has racks or indentations, fitted to the pins which we will call a a a. The bolt cannot pass until these pins are severally moved down by the lower levers at C. But the bolt has also two pins bb, held by the racks in the upper lever D, which must be raised at the same moment with the lower levers, or the bolt cannot pass. If any one of these five remains unreleased, there can be no movement to lock, or unlock.

The key has two bits F and G, acting on the levers C and D. F, with its three notches, moves the three levers C, which act severally on the pins a a a, whilst G, with its two notches, raises the two levers D, releases the pins bb, and at the same time throws the bolt.

The superiority of this lock consists, 1st. In its simplicity of parts and arrangement, greatly excelling in this respect the celebrated patent locks; 2nd, In the extra bit y, which constitutes, in fact, a double key, and adds exceedingly to the security of the lock; 3rd, That it is impossible to pick such a lock as this; the five stays, and the bolt itself, must all move together, or not at all, a thing which one might defy the most skilful pick-lock, with whatever tools, to effect, without the assistance of the key. Or

should not this be thought sufficient, the number of upper and under levers may be increased, each additional one adding, of course, to the security of the lock; 4th, An impression in wax, or any other composition, to imitate the key, would be of no avail; for so great is the exactness and accuracy of construction required, that even under the most favourable circumstance of having the key itself for a pattern, it would scarcely be possible to avoid leaving some one of the racks or pins untouched, which would render all the rest of the labour unavailing.

Deane's double-action levered lock has been submitted to the inspection of several practical and scientific men, who have given very high and laudatory opinions of its excellence and efficiency.

B.

MANUFACTURE OF SILK-WORM GUT.

Sir,-You would greatly oblige a numerous class of your subscribers, who, like myself, are fond of angling, if you would request some one of your correspondents competent to the task, to furnish you for publication in your Magazine, with a detailed account of the process for making silk-worm gut. This