PREFACE. THIS work advances no pretensions to originality. It is what its title indicates - A Manual. The subjects, therefore, of which it treats, must more or less have been handled before, and, no doubt, more ably, fully, and clearly. The scientific and mechanical explanations, which the writer has found it necessary to give in different parts of his work, are of course little more than repetitions of definitions and principles which many treatises supply; and if, in the statement of such principles, well known terms and formulæ of expressions have been employed, it must be recollected, that the language of science is technical, and from its arbitrary precisión forbids the use of any tongue but its own. The Publication of such a book may seem to require explanation, if not apology; and perhaps the best one the writer can give, will be found in the circumstances which suggested the work, and which have led to its appearance in print. In the course of a somewhat long and arduous professional career, the writer discovered, not unfrequently, considerable ignorance prevailed among Naval Cadets on points intimately connected with their duties. This may have arisen partly from their education, previous to entrance in the service, not being made to bear directly on its requirements, partly from the extensive range of information on various subjects required in a naval officer, and partly from the want of some plain works containing a good deal of instruction in short compass. As the writer has ever taken a lively interest in the improvement of young officers under his command, he was induced not only to direct their studies generally, but to assist them in those studies by a supply of papers, diagrams, and illustrations, calculated to throw some light on the subject before their minds. These papers grew upon his hands, and suggested the idea that, if collected and arranged, they might be of more extensive use to those youthful members of the profession for whose advantage they had been originally prepared; and that without the slightest intention of authorship. Under these impressions, the writer felt it his duty to place the following papers before the Lords of the Admiralty, leaving it to their judgment to decide whether they were likely to contribute towards the end desired, or whether they were only worthy of place among other well intentioned but useless writings which never see the light. Being himself entirely unambitious of the honour of authorship, and conscious that his etchings had but little claim on the favourable consideration of the public, he was contented to leave the question in the hands of his professional superiors, as an evidence, at all events, of his desire to serve a profession to which he has been all his life ardently attached. The decision of their Lordships left him no choice as to further steps. They were pleased to express a judgment that the pages laid before them were calculated to be useful, to intimate their approval of their contents, and to evince that favourable opinion in the strongest manner in their power by voting a sum of money towards the publication of the work, and still further by ordering a number of copies on their own account. This act, as liberal and encouraging on the part of the |