low pressure; and whether they ought to be made of cast iron or wrought

iron.

It is needless to enter minutely into the difference between the structure of the high and low pressure engines; the description, indeed, could hardly be made intelligible without plates. It is enough to say, that in the low pressure, called also the condensing engine, the power of the steam can, with no advantage, be raised above six pounds upon the square inch; it may be raised higher; but there is no temptation to raise it, because no increase in the propelling power of the engine would follow. In the high pressure, on the contrary, every increase of force which the steam receives, will produce a corresponding effect in the power of the engine; it will propel the boat or machine with the greater velocity. The conductors of steam-boats have, therefore, a temptation, when "bent on speed," to increase the power of the steam beyond what the strength of the engine can bear, and consequently to produce an explosion.

The steam-boat at Norwich had a high pressure engine. Mr John Taylor states, that it was proved to the pressure of 100 on the square inch, but that no more than 40 lbs. was usually applied. Mr Bramah conceives 60 lbs. to have been the usual pressure; but both are of opinion, that, at the time of the accident, it must have been upwards of 100.

The following are the leading statements on the comparative merits, beginning with those in favour of the low pressure:

Mr Bryan Donkin." Is it your opinion that a boiler could be made of proper materials, with safety valves, and under proper guard and direction, to make high pressure perfectly safe? -That would depend upon the quantity of pressure to be used; a safety valve might be carried to three hundred, or to any assignable force. I think that a high pressure engine may be made safe to a certain extent, but where they are left ad libitum, they never can be perfectly safe.

"Is it then your opinion, that in high pressure engines carried to that extent you mention, that danger would always operate ?-It would not always operate, but it would be extremely liable to accidents.

In fact, you yourself would not choose to use a high pressure engine, from the difficulty which exists, either more or less?-That is my opinion."

Mr Timothy Bramah, engineer at Pimlico." Do you think that a high pressure engine, under any guard that can be applied to it, is a safe engine to use in a steam-boat?-I do not conceive it is a proper engine, or a safe one."

Mr Henry Maudeslay, engineer, Lambeth.-" I never considered high pressure engines were applicable to boats, because the purpose of a high pressure engine is to save water, and water cannot be wanted on board a vessel; the difference between the one and the other makes no saving either in the weight or expence, taking it ultimately, particularly when steamboats are properly contrived. As far as my opinion goes as to steam-engines and steam-boats, I would not go from here to Margate in a high pressure boat."

He is afterwards asked, "According to your experience and knowledge. would a low pressure engine be safe in most cases that can occur?-I never knew a low pressure engine unsafe, but it appears that high pressure engines have been."

Mr George Dodd, an extensive proprietor of steam-boats on the Thames.-" Are all the steam-boats that you now have, or that you have had, used with condensing engines? -They are.

"Has any accident happened during the course of their being used?— The boilers of two have been injured by the imprudence of the engine workers; but no accident of any description could or has occurred to the passengers.

"Did you see the Norwich steampacket which exploded? I have been on board her, and perforined a voyage with her; I went down with a view of purchasing it; I went down for that purpose twice.

"What was your reason for not purchasing it?-Because it was a high pressure engine, and liable to the accident which has since occurred."

Mr Josias Jessop, civil engineer, Adelphi.-" There can be no doubt that an engine of low pressure must be more secure than one of high pressure; for although they may be both easily made secure originally, yet from

the natural wear and tear, both are liable to accidents. If an accident happen to one of a high pressure, its consequences certainly will be more dangerous than that of a low pressure engine."

The following testimonies go to prove a contrary opinion:

Alexander Tilloch, editor of the Philosophical Magazine.-" My opinion is, that, attending to what should be attended to in every steam-engine, and employing proper engineers, a steam-engine would be perfectly safe, whether with high pressure or low pressure."

Mr Andrew Vivian, miner, Cornwall." What accidents have happened to steam boilers within your own knowledge, working either with low or high pressure steam?-I have known of no accident with high pressure steam and cast-iron boilers; but I have known an accident happen working with Boulton and Watt's low pressure engine, which was on the 28th of November 1811, in Wheal Abraham mine; a wrought-iron boiler working with low pressure steam exploded there, and scalded six men, three of whom died in the course of a week afterwards. The steam from low pressure scalds much worse than the steam from high pressure."

Mr Thomas Lean, engineer for Cornwall miners.-" You are then well acquainted with steam-engines of every various construction?-Certain ly I am; I see fifty-seven every month.

"Do you conceive that there is any material difference in the respective safety of those engines ?-Some of the engines are certainly safer than others.

"Be so good as to state which, and why?-I conceive there is no danger whatever in the use of high pressure steam-engines; and for this reason, that, in general, for an engine that is intended to be worked with high steam, the materials are made stronger in proportion than the materials used for steam of low pressure."

I shall now collect the evidence in regard to the comparative merits of a cast or of a wrought iron boiler.

Mr John Taylor." Have you ever seen an explosion of a cast iron boiler?-No, I have not. I have seen the effects at Wells Street; I was upon the ruins immediately af

ter; the effect seemed to be tremendous; there it knocked down the whole building, which was a sugar-house of five or six stories high, and fragments appeared to be thrown in every direction; the boiler itself was shattered into a great number of pieces.

"If that had been a wrought iron boiler, and had burst, it would not have produced the same effect?—I think not."

Mr William Chapman.-" Would you not always recommend a boiler to be made of wrought metal on board steam-boats?-On board steam-boats I would recommend them all to be made either of copper or charcoal iron plates, beat under the hammer and not rolled; the resistance of cylindric boilers will be in the inverse ratio of their diameters."

Mr Philip Taylor." The boilers I have generally employed are constructed of malleable iron, commonly known by the name of charcoal iron, rivetted together and secured by strong wrought iron belts. From observing the danger arising from the introduction of flat cast iron ends, I have terminated the ends of the boilers by wrought iron ones, nearly hemispherical; this mode of construction, as far as my experience goes, combines more strength and durability than any other."

Mr Henry Maudeslay." What is your opinion as to the comparative safety of cast and wrought metal used in boilers?-I consider that wrought iron is extremely safe, compared to cast iron.

"Then, at all events, it is your opinion, that, in steam-boats, boilers of wrought metal should be used in preference to cast?-No doubt about it.

"Do you think there is any material difference between the use of copper and wrought iron?—No, excepting in the greater degree of corrosion to which iron is liable."

Mr Alexander Galloway.-" Under all the circumstances of the case, I should most decidedly recommend a condensing engine, a condensing engine with a wrought iron boiler; because, when cast iron becomes subject to high expansion and contraction, the constant repetition of these effects in a very great degree impairs the strength of the boiler."

Mr John Braithwaite." Would

you not recommend on board steam boats, wrought metal boilers to be used in preference to cast?-Certainly; I have made some discoveries myself in the boilers I have put up, which makes them perfectly safe."

Mr John Hall." I make boilers in cast iron, and I have proved them by an hydraulic press made for the purpose, and have gone as high as 250 pounds to an inch, and that I considered enough; nothing happened.

Mr Alexander Tilloch.-"I would prefer cast iron, contrary to the opinion of many people, and the reason I would prefer it is the same for which it is preferred in making cannon. It is not possible to get thick plates of wrought iron perfect throughout, and you trust at last to rivets in joining them, but cast iron boilers can be made of any strength you please; instead of having a boiler that will stand sixty, it may be made to stand six hundred, of either wrought or cast iron. Another reason why I would prefer cast iron is, that the sheet iron corrodes much quicker, and destroys by oxydation, so that a boiler may be safe when first set up, and stand its proof, but very soon become unserviceable, or at least comparatively so."

Mr John Steel." Will you give your opinion as to the comparative merits of wrought and cast iron? I cannot conceive as to the safety of the two, that there is any difference whatever, when the steam is used, as it generally is, for high pressure engines to 40 pounds to the inch. If it was required to make the strongest boiler imaginable, I should consider cast iron preferable, because there you can get to an unlimited strength of resistance; wrought iron you can only have of a certain thickness."

Mr William Brunton.-" What injury do you think is likely to arise from the bursting of a high pressure boiler, composed of wrought iron ?-I conceive the injury would be more partial, in consequence of the fragments being larger; for I do not suppose that the wrought iron boiler would be divided into so many parts as a cast iron boiler would.

“In a steam-boat, what boiler would you most recommend to be used to insure safety to the persons on board; a wrought iron or a cast iron

boiler?-A wrought iron boiler, properly constructed."

Mr Josias Jessop." I think that if the boiler were made of malleable metal, such as iron and copper, it would be an additional security.

"What is the ground of your preference to malleable or wrought metal?It does not burst by an explosion, as brittle metal does, but tears; it would probably rend at the joints.

"You do not mean then to say, that it would be impossible that a malleable boiler would burst, but that it is improbable that it would ?—It would burst, but it would not fly in pieces; the rent would create a natural safety valve."

Mr Arthur Woolf, engineer, Cornwall." Are your boilers in general made of wrought or cast iron ?—Of cast iron wholly; I approve of the cast iron boilers in preference to any mixture of metals.

"Do you consider that the cast iron boiler, upon the common construction, is equally safe with a wrought iron one?-Not upon the cominon construction that I have seen; some I should have doubted very much; I have seen some that are rather dangerous; my patent consists of one composed of a number of tubes.

Suppose a cast iron boiler, and a wrought iron boiler of about the same form and capacity, to be exploded by the force of the internal steam, do you think that the mischief likely to be produced by each of those would be equal; taking any form you please, and exploding both, which would do the most mischief?I do not think the wrought iron boiler would separate into so many pieces as the cast iron boiler.

"Then do you think that the explosion of the wrought iron boiler is attended with as much danger as the cast iron boiler?-In every thing, excepting what depends upon the fragments of the iron itself; I have no hesitation in saying that cast iron boilers are safer than wrought iron boilers."

Mr Andrew Vivian." Do you conceive that there is any difference in the liability to explode between the boilers constructed of wrought and of cast iron ?-I should conceive that cast iron could be made much stronger than wrought

iron with less difficulty; I conceive it to be a very difficult thing to make a wrought iron boiler so strong as we can have it cast; we have some of our boilers made two inches thick; and to make a wrought iron boiler equally strong as that, would be very difficult to be accomplished by work

men.

Supposing the only object to be safety to the lives or limbs of the persons who should be surrounding the engine, would you in that case prefer having the boiler of a high pressure engine of wrought or of cast iron? -I would have cast iron, because it can certainly be made stronger than wrought iron for the same expence."

Mr Thomas Lean." Have you any choice, in point of safety only, between a boiler constructed of cast iron or of wrought iron?-Were I to have a boiler where I wished to have the greatest strength, I would certainly have it made of cast iron; I have not one doubt that a cast iron boiler can be made much stronger than it is possible to make a wrought iron one; in fact, the explosions that we have had in Cornwall have all been in wrought iron boilers, but I never had one in cast iron boilers, nor have we had an accident from high pressure steam; all the accidents have been from low pressure steam in Cornwall."

Having thus extracted the substance of the examination, so far as relates to these two leading questions, I shall now beg leave to make a few observations.

The Committee report, that the persons examined "generally agree, though with some exceptions, that those called high pressure engines may be safely used, with the precaution of well constructed boilers, and properly adapted safety valves." Now, I cannot exactly agree with the Committee in this general inference. A great majority, I think fully twothirds, are decidedly against the high pressure engines. It is farther to be observed, that these persons include almost all who have had any observation of, or concern with steam-boats; while the advocates of high pressure are almost all persons connected with the application of steam to machinery used in manufactures. They are, indeed, almost exclusively the persons

VOL. I.

who construct engines for the use of the Cornish miners. When employed for that purpose, there appears to be a great saving, in point of economy, in the use of high pressure engines. Without, however, supposing any bias from this cause, the two cases are different, and different rules may apply to them. It would seem, by the testimony of those concerned in steamboats, that the low pressure boilers burst almost as often as the high pressure; but, in bursting, they do no injury; the fragments never explode. The only danger is from the scalding of the steam; but this seems never to have been experienced in boats, probably from the covered state of the engine; it occurred only in mines or manufactories, where the workmen were exposed to the steam. It appears to follow, therefore, that his Majesty's subjects may travel in boats using low pressure engines, with perfect safety to life and limb. Moreover, these boats seem, in all common cases, capable of sailing with every degree of rapidity which can be wished for. The steamboats on the Clyde go, I believe, at the rate of seven or eight miles an hour, which is as rapid sailing as any one could desire or choose. There seems no motive, therefore, for encountering the hazard of explosion, which probably can never be entirely prevented in high pressure engines. I am not prepared to say, that the Le gislature ought absolutely to prohibit the use of boats with such engines; because I share the feeling of the Committee, that as little restraint as possible ought to be placed on the natural course of human industry. I only conceive, that, unless in very peculiar and special cases, the use of high pressure engines in boats can serve no purpose, and ought to be entirely discouraged. The Committee also appear to me to be departing from their own principle, when they load all steamboats indiscriminately with troublesome and expensive regulations, which seem to be necessary or applicable only in the case of those using high pressure engines. If the bursting of low pressure engines never produces any damage, why require, before every voyage, an examination by an engineer, whose presence it may be difficult and expensive to procure?why also demand, that the boiler should be made capable of bearing six

D

times the pressure which it is intended to sustain?

The Committee also report, that a great majority of opinions lean to boilers of wrought iron or metal, in preference to cast iron;" and they therefore recommend as a regulation, "that all boilers belonging to the engines by which such vessels shall be worked, should be composed of wrought iron or copper." Generally speaking, the same persons who recommend low pressure engines, recommend wrought iron; and those who advise high pressure engines, advise cast iron. We do not exactly know why the Committee has adhered to the former in the one case, and to the latter in the other. The general result seems to be, that cast iron boilers may be made stronger than wrought iron, and consequently less liable to explode; but when they do explode, they occasion more damage. On these grounds, the preference between the two appears somewhat of a dubious point. But, at all events, as the only object in the use of wrought iron is to diminish the injury produced by an explosion, I can see no possible motive for compelling the adoption of it in low pressure engines, which never explode. The hardship of such a regulation would also be very considerable, as it would render useless all the low pressure engines at present composed of cast iron, and oblige the proprietors to incur the expence of a new machine. Upon the whole, the result of the evidence here collected appears to be, that there is no ground for giving any encouragement to the use of high pressure engines in steam-boats. But, if any proprietors choose to set such on foot, it is very proper that they should be made liable to the regulations proposed by the Committee. To impose, however, the same regulations upon ali steam-boats, appears to be both unnecessary and vexatious.

varieties of organized life, or the diversified appearances of the laws of nature, which are there presented. The facts which I have to notice are not, besides, very generally known, and seem, on both these accounts, to be deserving of a place in your useful miscellany.

1. My first observation relates to that species of marine animal which is known to naturalists by the name of Medusa Capillata. It is a frequent inhabitant of most of the shores of this island, and may easily be distinguished from the other species of the same animal, by the remarkable transparency of its whole mass; and more particularly by some beautiful spots of bright purple, which are placed near the centre of its disk. I ought, perhaps, to remark, for the sake of some of your readers, that the class of animals, of which that alluded to in the following observation is a species, is commonly known in this country by the name of the sea-blubber, and is remarkable for several striking properties, which characterize some of its species, such as that of occasioning a feeling of irritation in the skin when touched, and of being phosphorescent in the dark. To a common observer, all the varieties of this animal appear to be merely masses of a transparent jelly, scarcely worthy of being ranked among the class of animals, and parently driven, without the power of directing their course, by the varying direction of the winds or the waves. If, however, on a fine day, when the sea is calm, and when one of the spe-cies to which I now allude is swimming near the shore, an attentive eye be kept upon its movements, within a yard or two of the place of the animal, the following very beautiful and amusing appearance will be observed: As the animal moves forward, it is constantly employed in forming its disk into a greater or less degree of convexity, while at every such change in the form of its mass, a fringe of most beautiful and apparently silky filaments, all around the circumfe rence of the disk, is protruded into the water, and again withdrawn into the body of the animal, as it resumes its ordinary and more flattened appearance. These filaments proceed from the circumference of a circular space, which is placed near the centre of the animal, and may be distinctly secu

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