Page images
PDF
EPUB

PREFACE.

The science of Mechanics is of 80 much importance to a commercial nation, that every attempt, either to elucidate its principles, or to extend its various branches, must ultimately prove beneficial to the whole community.

community. Should the Author's motives for publishing this work required, he wishes to observe that the Public are in possession of very few books on this subject, and, among these, not one can be found which is suited to Academical purposes : an easy sompendium was wanting, and he drew up the following sheets with the view of abridging the labors of those Gentlemen who are in the practice of instructing youth in those useful studies.

The English Author's 'who have written expressly on this subject are, Emerson, Parkinson, Wood, and Gregory, with a few others-Emerson's mechanics was an excellent performance. at the time it was published, but it cannot be denied that subsequent improvements have, in some degree, diminished its utility; and it may be truly affirmed that it never was suitable, for ever wds intended for a School-book :the same may be said of Parkinson's work. Wood's small piece in the Cambridge Courseis entirely devoted to the theory; and, therefore, however excellent it may be in that department, it must necessarily be deficient in such information as is requisité in . opplying the theory to practice in the Arts, and in the

construction of machinery. The size and price of Dr. Gregory's very scientific work preclude it from being generally used in Schools ; it is, also, too difficult to be understood by the generality of Studentsto that work the present may serve as an Introduction. Considerable experience as a Teacher has convinced the Author that Introductory books cannot be rendered too plain and easy for the capacities of youth are exceedingly various, and though some few are capable of making rapid strides, and stop at nothing, yet it is a melancholy reflection to think that a far greater number must be led by the hand, must be assisted at every step, and require that every obstacle should be removed.

In short, it is the business, it is the duty also, of preliminary. writers, to make the road as smooth and easy as their materials will admit; to lay the ascent gently sloping, and endeavour as much as possible to dispel the mists which but too frequently intercept the view.

The present work is divided into five Books, the first of which contains the elements of Statics, or the doctrine of the Equilibrium of solid bodies. The two first sections in this book are taken, with considerable alterations, from la Statique de Monge; and here it must be observed that the principle on which the first section is founded, has been objected to, as depending on a property of the straight lever, which ought to have been previously demonstrated; the proposition has in fact been demonstrated, without any reference to the straight lever, by making use of a principle which the celebrated Leibnitz called a sufficient reason ;but it is itself nearly selfevident, without any demonstration; the mind assents to it as a fact, wilhout any hesitation; and if we may be permitted to consider it as an axiom, all that follows is as strictly demonstrated as the most scrupulous in these matters could desire: the remaining sections are in a great measure altered from some of the best of our English Writers. The

[ocr errors]
[ocr errors]

language of other Authors, however, has scarcely ever been adopted, except in the description of machines ; every article has been written de novo, and in demonstrating a proposition, after having carefully considered the several demonstrations of former writers, if he could not, according to his own judgment make out a plainer, he has inserted the substance of the easiest he could find; after this confession the reader will perhaps not be surprized when he finds, on perusing the work, that the Author has not always cited his Authoritieshe has however mostly done 80, and especially when it was necessary to inform the Student where he might meet with more ample information, when farther information might be required.

This method has been carefully followed throughout the whole work; and as no claims to originality are advanced, he will feel insensible to any charges of plagiarism that may be urged against him.

To arrange the leading principles of a science in proper order, or so that a regular and dependent concatenation of ideas may run through the whole, is no very easy task to perform; this the Author thinks he has in some degree accomplished, and, though a great number of articles are entirely new, this is all the merit he claims for his undertaking. The examples added to almost every section will be found of much service in firing the principles in the mind, and great care has been taken not to introduce any example, the method of doing which had not been previously laid down in the preceding articles. The practical remarks, scholia, and description of machines, will show how to apply the theory, and both together cannot fail of relieving the Student from the disagreeable tedium which he always feels when studying the theory alone.

The second book treats of DYNAMICS, or the doctrine of motion, and as this subject is extremely copious, little more than an abstract of the most useful branches of this science can be expected ; the Student will, however, find sufficient information to enable him, after he has studied what is here given with attention, to pursue the subject in other works where this doctrine is more fully detailed.

The THIRD BOOK contains the principles of HYDROSTAtics and HYDRODYNAMICS, or the principles of the equilibrium and motion of non-elastic fluids. In this book the theory and practice are so blended, and the subjects treated in such a manner, as to render it of use to readers in general.

In the fourth book, PNEUMATICS, or the properties of elastic fluids in general, though more particularly the properties of common or atmospheric air, are explained.

This book though short, will be read, it is hoped, with much pleasure, as it contains a considerable fund of information treated in a popular manner : beside the description of several smaller instruments, as the barometer, the thermometer, the syphon, pyrometer, 86. it contains the theory and description of pumps, that is, of the AIR-PUMP and four WÁTER-PUMPS; tiz. the SUCKING, the LIFTING, the FORCINO, and the CENTRIFUGAL PUMP.

In the first four books the subjects are prosecuted as far as could be done without introducing the Fluxional Calculus; but to render the work of more general utility, and to accommodate Students in the higher Classes,, a FIFTH BOOK is added, in which several branches in the preceding books are considerably extended.

This fifth book contains also the motion of machines and their marimum effects, an account of water-wheels, experiments on friction, and the theory of wheel-carriages.

But for a more particular account of what each book contains, the reader is referred to the Index or Table of Contents.

It was also with a view of rendering the work useful to PRACTICAL MECHANICS, as well as to STUDENTS, that the Scholia with the many practical rules and observations,

« PreviousContinue »