A text-book on natural philosophy for the use of schools and colleges, Book

PREFACE.

The success which has attended the publication of my Text-Book on Chemistry,” four large editions of it having been called for in less than a year, has induced me to publish, in a similar manner, the Lectures I formerly gave on Natural Philosophy when professor of that science.

It will be perceived that I have made what may appear an innovation in the arrangement of the subject; and, instead of commencing in the usual manner with Mechanics, the Laws of Motion, &c., I have taught the physical properties of Air and Water first. This plan was followed by many of the most eminent writers of the last century; and it is my opinion, after an extensive experience in public teaching, that it is far better than the method ordinarily pursued.

The main object of a teacher should be to communicate a clear and general view of the great features of his science, and to do this in an agreeable and short manner. It is too often forgotten that the beginner knows nothing; and the first thing to be done is to awaken in him an interest in the study, and to present to him a view of the scientific relations of those natural objects with which he is most familiar. When his curiosity is aroused, he will readily go through things that are abstract and forbidding; which, had they been presented at first, would have discouraged or perhaps disgusted him.

I am persuaded that the superficial knowledge of the physical sciences which so extensively prevails is, in the main, due to the course commonly pursued by teachers. The theory of Forces and of Equilibrium, the laws and phenomena of Motion, are not things likely to allure a beginner; but there is no one so dull as to fail being interested with the wonderful effects of the weight, the pressure, or the elasticity of the air. It may be more consistent with a rigorous course to present the sterner features of science first; but the object of instruction is more certainly attained by offering the agreeable.

But though this work is essentially a text-book upon my Lectures, I have incorporated in it, from the most recent authors, whatever improvements have of late been introduced in the different branches of Natural Philosophy, either as respects new methods of presenting facts or the arrangement of new discoveries. In this sense, this work is to be regarded as a compilation from the best authorities adapted to the uses of schools and colleges.

Disclaiming, therefore, any pretensions to originality, except where directly specified in the body of the work, I ought more particularly to refer to the treatises of Lame and Peschel as the authorities I have chiefly followed in Natural Philosophy; to Arago, Herschel, and Dick in Astronomy. To the treatises of M. Peschel and the astronomical works of Dr. Dick I am also indebted for many very excellent illustrations.
Those subjects, such as Caloric, which belong partly to Chemistry and partly to Natural Philosophy, and which, therefore, have been introduced in my text-book on the former subject, I have endeavored to present here in a different way, that those who use both works may have the advantage of seeing the same subject from different points of view. The laws of Undulations, now beginning to be recognized as an essential portion of this department of science, I have introduced as an abstract of what has been written on this subject by Peschel and Eisenlohr.

It will, therefore, be seen that the plan of this work is essentially the same as that of the Text-Book on Chemistry. It gives an abstract of the leading points of each lecture—three or four pages containing the matter gone over in the class-room in the course of an hour. The lengthened explanations and demonstrations which must always be supplied by the teacher himself are, therefore, except in the more difficult cases, here omitted. The object marked out has been to present to the student a clear view of the great facts of physical science, and avoid perplexing his mind with a multiplicity of details.

There are two different methods in which Natural Philosophy is now taught:—1st, as an experimental science; 2d, as a branch of mathematics. Each has its own peculiar advantages, and the public teacher will follow the one or the other according as it is his aim to store the mind of his pupil with a knowledge of the great facts of nature, or only to give it that drilling which arises from geometrical pursuits. From an extensive comparison of the advantages of these systems, I believe that the proper course is to teach physical science experimentally first—a conviction not only arising from considerations respecting the constitution of the human mind, the amount of mathematical knowledge which students commonly possess, but also from the history of these sciences. Why is it that the most acute mathematicians and metaphysicians the world has ever produced for two thousand years made so little advance in knowledge, and why have the last two centuries produced such a wonderful revolution in human affairs It is from the lesson first taught by Lord Bacon, that, so liable to fallacy ara the operations of the intellect, experiment must always be the great engine of human discovery, and, therefore, of human advancement.

To teachers of Natural Philosophy I offer this book as a practical work, intended for the daily use of the classroom, and, therefore, so divided and arranged as to enable the pupil to pass through the subjects treated of in the time usually devoted to these purposes. A great number of wood cuts have been introduced, with a view of supplying, in some measure, the want of apparatus or other means of illustration. The questions at the foot of each page point out to the beginner the leading facta before him.

John William Draper.
University, New York,
July 10, 1847.