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of contact; whereas, when the rubbing surfaces are very true, the oil is spread over them in a thin film, and metallic contact is prevented. In the engines of the 'Hercules,' which are of 1,200 nominal horses' power, the speed of piston is 648 feet per minute, which is nearly as great as the speed of the engine of the steamer 'Barwon' constructed by me in 1854. In many steam vessels a pressure of steam of 60 lbs. and upwards is now employed. These engines are fitted with surface condensers; and the steam after acting by high pressure in one cylinder is dismissed into the other, where it acts as low pressure steam. The consumption of coal is reduced by this arrangement to about 2 lbs. per actual horse power per hour.

The steam engine, however, it appears to me has now nearly fulfilled its destiny; and believe it to be on the eve of supercession by other motors, which will differ materially from the existing steam engine, though steam may still be used in them to some extent, but not exclusively, and only in combination with other fluids. Under this belief I have undertaken the production of a work on motive power engines, whether propelled by air, or gas, or steam. I hold it to be the function of any competent authority upon such subjects to lead public opinion instead of following it; nor should such a guide content himself merely with the func

tion of chronicling the circumstances of contemporaneous achievement. My constant aspiration has been, while recapitulating the nature and details of the best existing arrangements, to discuss their congruity or otherwise with those sound mechanical principles which I have endeavoured to explain, and thus to combat the heresy that there is any finality in existing arrangements or systems; the fact being that the existing steam engine is a most imperfect machine, so that it should be the object of intelligent ambition to produce something better. It is indeed no small work to lift the veil of the future, and out of a chaos of abortive schemes and of principles of action in the application of which no practicable method has yet been discerned, to construct a system which will supersede that which at present exists, and which the ablest minds have been unable, after a century of effort, very materially to improve. But the task I now propose to myself is not merely to show that a better engine than the present steam engine can be made, but how it can be made; and it is not to be supposed that I should have spoken with the confidence I have done of the early supercession of the steam engine if I had not seen my way in this important work.

J. BOURNE.

LONDON: May 10, 1869.

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RECENT IMPROVEMENTS

IN

THE STEAM ENGINE.

In this Supplement to my Catechism of the Steam Engine I propose to recapitulate the most useful information I have been able to collect respecting all recent improvements which have been made in the Steam Engine.

As that work addresses practical engineers, and not mere desultory or superficial inquirers, it is indispensable that the information it affords should not only be intrinsically sound and practical, but that it should be cleared of all tinge of antiquity. In an art so rapidly progressive as mechanical engineering, the knowledge of ten years ago is no longer adequate to satisfy the wants or direct the operations of present practice; and, under this conviction, it has appeared to me that the time has come when it would be proper to review the information which the catechism contains, in order that it might be rendered more conformable to the accredited maxims of the

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time, and also that reliable information respecting altered modes and new improvements might be fully afforded. To this end I have carefully revised the text of the last edition; and I have introduced such alterations into it as appeared to me to be necessary to make the work consistent with the best indications of modern practice. But these alterations have not been numerous or extensive, as I found that although there was a good deal to add there was little to alter; and it seemed to me that the requisite additions could be much more conveniently made in a separate discourse, which would be supplementary to the work, and which might be purchased separately by the possessors of the former editions, than by incorporating such new information in the body of the work itself, whereby it would be rendered inaccessible to all who did not feel disposed to purchase the entire volume. Under these convictions I have proceeded to prepare the present supplement; and I trust that it will be found to answer its intended purpose of giving an accurate and vigorous outline of contemporaneous engineering knowledge in its most select manifestations, and that it will set the reader face to face with the works and opinions of those who are justly accounted the leaders of the art, so that he will be able to feel that he has been brought up to the highest point of information yet reached by the most eminent practitioners. It is this vitalizing species of knowledge which alone renders engineering works of much value; and the place of it can never be supplied by

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