Mr. Dodd estimates the expense of completing a vessel of a hundred tons burden, and drawing four feet six inches water, at about six thousand pounds; while the first cost of a steam-boat on Mr. Symington's plan, doing the work of about twelve horses, and travelling at the rate of two miles and a half per hour, has been estimated at about eight or nine hundred pounds. The consumption of coals however, in this and in all other engines connected with steam navigation, is much more considerable than when employed on land. In a fourteen-horse power engine, on Messrs. Boulton and Watt's construction, they consume 1 cwt. 1 qr. 20 lbs. per hour of good Newcastle coals: while an engine of thirty-three horses' power, requires a proportion scarcely equal to two-thirds that quantity.

The employment of high-pressure engines for the purpose of steam navigation, has unfortunately given rise to a considerable prejudice against the general use of this economical and expeditious prime mover. The attention of the legislature was first drawn to this subject by the explosion of a high-pressure boiler in a vessel employed for the conveyance of passengers in the neighbourhood of Norwich, on which occasion the consequences were of the most terrific nature. As, however, the matter was very fully examined by the Committee of the House of Commons, appoint

ed to inquire into the various particulars connected with this unfortunate catastrophe, we shall content ourselves by referring the reader to the important facts contained in the annexed abstract, which fully demonstrate the possibility of constructing a steam vessel, uniting the essential qualities of safety, economy, and celerity.

CHAPTER IV..

Abstract of Evidence before a Select Committee of the House of Commons on STEAM NAVIGATION.*

MR. BRYAN DONKIN was called in and examined. Witness went down to Norwich, as a volunteer, to inquire into the cause of the explosion of a steam-boat. Was accompanied by Mr. Timothy Bramah and Mr. Collinge. Was of opinion that the immediate cause of that explosion had been the use of steam of a very high expansive force; the approximate cause was a deficiency in strength of the end of the boiler. The boiler was cylindrical. The cylindrical part, and one end, was wrought iron; and the other end

* The Committee commenced its sittings May 8, 1817, and consisted of the following highly respectable individuals:-Charles Harvey, Esq. in the chair; Mr. William Smith, Mr. Davies Gilbert, Sir Martin Folkes, Sir James Shaw, Sir William Curtis, Sir Charles Pole, Mr. Alderman Atkins, Mr. Williams Wynn, Sir Edward Kerrison, Mr. Lacon, Mr. Shaw Lefevre, General Thornton, Mr. Edward Littleton, Mr. Finlay, Mr. Leader, Mr. Alderman Smith, Mr. Wrottesley, Mr. Barclay, Sir James Graham, Mr. Swann, Mr. Charles Dundas, Mr. Holmes, Mr. Thompson, and Mr. Bennet.

On the 14th of the same month, Sir Matthew Ridley and Mr. Ellison were added to the Committee.

was cast iron. It appeared to have been previously of wrought iron, but, for some reason, the wrought iron end had been cut out, and a cast iron end substituted in its place.—Was of opinion that any high-pressure boiler so constructed was unsafe. The difficulty of obtaining a proper degree of strength at all times, in the materials of which the boilers were made, arose from the constant deterioration which they must be suffering from the action of the fire, and from the various degrees of expansion and contraction, operating on different parts of the boiler.-Would not choose to use a high-pressure engine, from the danger which arose from their use.-Thought it just to state to the Committee, that there was an advantage to be derived from the use of high-pressure engines on board of boats, which were necessarily loaded differently at different times.

This different loading required a different power in the steam engine, and the high-pressure engine was capable of having the additional power given to it without difficulty; whereas, in the lower-pressure engines, they were confined to the power first assigned them.-Scarcely ever saw the low-pressure engine beyond six pounds to the inch.-Had known one boiler worn out in six months, and another used for seven or fourteen years. The strength of cast-iron boilers was extremely uncertain: cast iron was liable to contract in various degrees in different places, and therefore was liable to break.-Thought that all cast-iron boilers were dangerous when used for steam of high expansive force. It was more practicable to make a boiler of the malleable metals to resist a high pressure, as far as the tenacity of the metals was concerned; but another difficulty occurred which prevented the application of the malleable metals to boilers for high-pressure engines, which was that of rendering the joining of the plates secure.-Believed

that wrought-iron boilers were much less frequent than the cast-iron boilers, and in Woolf's engines they were scarcely used at all. Should think that the cast-iron boilers would be cheaper than wrought, if made of equal strength.-Considered that in case of the explosion of a cast-iron or a wrought-iron boiler, the cast-iron would be attended with the greater danger.

In employing the malleable metals a simple rending generally took place, so that it would seldom happen that the upper part of the boiler would be torn off; but, in a cast-iron boiler, the fragments would be scattered about, and be more destructive. The boilers invented by Mr. Linns and Mr. Woolf were all of them cast iron. Mr. Woolf's had been in use nearly ten years. Considered low-pressure boilers safe from explosion in all instances, used with no farther pressure than six pounds.-Had seen very few boilers constructed for the purpose of a low-pressure engine, or a condensing engine, that would sustain a pressure of ten pounds without occasioning considerable leakage, or without forcing the joints.-Had never heard of an explosion with the low-pressure boiler of any consequence whatever, merely a giving way of the plates, or the wearing out, not such a bursting as could be called an explosion.— Conceived Woolf's mode of constructing boilers to be a considerable improvement,-a very material one. Had likewise been told, though without having seen one, that Trevethick had invented a method of making boilers by increasing their length and decreasing their diameter, so as to render them capable of sustaining pressure to a much greater degree than heretofore.-In high-pressure engines the expansive force of steam was very variable, from thirty pounds to one hundred and twenty pounds upon the square inch, or even perhaps higher than that. Instances had been known in which a boiler had been worked at one