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

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 maximum of speed be attained.

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

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Fourthly, The separation of the engines and paddles from the hull by the intervention of springs.

Fifthly, Galvanization of the iron to prevent decay.

Sixthly, Experiments on a large scale to compare the sculling and paddling processes.

I remain, Sir, yours, &c.
JUNIUS REDIVIVUS.

October, 1838.

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 g, 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

article, so essential to our gentle art, comes chiefly, I am told, from Spain and Turkey; but of late years nothing but gut of a very inferior quality has been imported, and the London fishingtackle makers all declare that really good, strong, and sound salmon gut is not to be procured for love or money. Owing to this scarcity, a most extravagant price is demanded, and it is surprising that, considering the great profit which the wholesale importers would derive from taking a little pains to induce the manufacturer to make a better article, nothing of this sort has ever been attempted. As far as I can learn, the process is exceedingly simple, and is generally performed by women or children, who take the silk-worm as it is about to spin its cocoon, and draw it out into a glutinous thread between their finger and thumb, fifteen or twenty inches in length, when it hardens, by exposure to the air, and is made up into hanks or skeins containing one hundred such lengths or threads. This operation would appear to be performed in the most careless manner, as in such hanks there are seldom more than a dozen or two good round pieces of gut, the rest being all "stale, flat, and unprofitable." The retail price of a hank varies from sixpence to two or three guineas, according to quality! Now, if there be no mystery in the art, and any silk-worm in a proper state be capable of being converted into a length of gut, we may calculate the profit to be made on one hundred silk-worms when converted into a three-guinea hank. What occurs to me, in my ignorance of the real process, is, that the glutinous matter of the worm might, at some time or other before it hardens into the beautiful transparent thread which it ultimately becomes, be rolled, or be drawn through a gauge, so as to ensure its being of an uniform thickness and roundness for a certain length, such as we sometimes find it. One-third of the length is always quite useless; but why it is so I do not know. Now, as we have in India every variety of silk-worm, and some of them of the wild species, yielding a particularly strong silk, which is often spun into fishing-lines, all that is wanting is to instruct our countrymen who have extensive filatures in Bengal, in the process of making silk-worm gut

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with such improvements (if practicable) as I have suggested, and to make them aware of the extent of the demand for it as a marketable article, and it cannot be doubted that, ere long, we should draw all our supplies from our own territories in the east, instead of being indebted, as hitherto, to foreign countries. May I hope that you will bring this subject into notice by calling for information regarding it, and perhaps some ingenious person may be induced to make a few experiments with the silk-worms reared at home, and ascertain whether it be possible by some such means as are above alluded to, to manufacture a superior article to what is generally to be found in the shops. Amateur anglers will tell you that they frequently pay sixpence or a shilling for single threads or hairs of salmon gut, and would gladly purchase whole hanks if they were to be had. I know not what quantity of silk-worm gut is annually imported into England, but this could be ascertained at the Custom-house, and would prove to the proprietor of a silk-worm establishment that it would be well worth his while to turn his attention to the manufacture of it on a large scale. I remain, Sir, &c.

Edinburgh, October 9, 1838.

PISCATOR

FRENCH AND ENGLISH FIREMEN.RESCUE SERVICE, &c.

Sir, I am much obliged to Mr. Felix M. Simeon, for the complimentary remarks with which he introduces his communication, at page 94 of your 791st Number; but I must be permitted to show, that while charging me with error, he has fallen into considerable error himself.

An attentive reader would hardly have supposed that when I was speaking of, and offering advice to, honorary firebrigades in England, or the voluntary fire-associations of the Continent, I could have included in either of these classes, the numerous and well-trained force of the French Sapeur Pompiers. No volunteer force, I apprehend, can ever hope to rival, either in point of numbers or discipline, the military firemen of Paris. In our own case, it would be absurd to expect that any "posts" can be established-" detachments sta

tioned at proper intervals," or, "men kept constantly on guard and always ready." Nor is such a service at all likely to be extensive enough, "to be formed into three divisions, each under the superintendence of an experienced officer," so as to undertake simultaneously and independently, the rescue of property, attack of the fire, supply of water, &c. With this explanation, I proceed to notice the comparison instituted by Mr. F. M. Simeon, between the Sapeur Pompiers of Paris and the fire-engine establishment of London, as well as the fire-police of Edinburgh and Manchester.

Mr. Simeon states, that if we take into consideration the immense size of the houses, their construction, the difficulty of excluding air, &c., we shall find the parallel between them much in favour of the first." But how this comes about is by no means clear, at least to my limited comprehension. If the immense size of the buildings is to be considered, neither London, Edinburgh, nor Manchester, are much behind the Parisian capital, the size of the Edinburgh houses is notorious.

With respect to "their construction," "difficulty of excluding air," &c., London buildings stand pre-eminent. The circumstance of the existence of stone stairs throughout the Parisian houses, is one of the greatest safeguards against the rapid spread of fire that can possibly be devised, and I have more than once or twice asserted in your pages, that the general introduction of incombustible stairs would tend more than any other provision that could be made, to limit the extent and diminish the danger of London fires; in fact, it would completely change their character.

There is considerable disparity in point of numbers between the corps alluded to; the Sapeur Pompiers of Paris are, I believe, one thousand strong; the fire-engine essablishment of London musters not quite one hundred; while Edinburgh is very efficiently protected by eighty firemen, Manchester by forty! The extent of ground, number of buildings, and value of the property effectually protected by the London fire establishment, may be set down as being ten times greater than in Paris; and yet, after the burning of the "Theatre Italia" in January last, M. Paulin, the Col. Commandant of the Sapeur Pompiers, required an augmentation of his force, as being too few.

Besides, in Paris all classes of persons turn out to assist in extinguishing fires and in addition to the firemen, there may usually be seen private citizens, National Guards, troops of the line, Municipal Guards, Sergens de Ville, and police officers, all actively employed. The French laws are exceedingly strict in compelling all passers-by-whether the fashionable beau in his ball dress, the lowest of the canaile, or the monarch himself to hand the water or pump the engines as he may be directed. At the conflagration of the "Theatre Italia," a number of well. dressed persons who had just issued from Musard's ball, and also from the concert of M. Valentino, submitted with the best possible grace, to join the chain, and pass the water-buckets, notwithstanding the intense cold which prevailed at the time.

The following table will show at a glance the relative proportions which the fires in the two capitals bear to each other; viz.