THE

ELEMENTS OF PHYSICS

BY

HENRY S. CARHART, LL.D.

PROFESSOR OF PHYSICS IN THE UNIVERSITY OF MICHIGAN

AND

HORATIO N. CHUTE, M.S.

INSTRUCTOR IN PHYSICS IN THE ANN ARBOR HIGH SCHOOL

' REVISED EDITION

Boston

ALLYN AND BACON

AND CHICAGO

HENRY S. CARHART AND HORATIO N. CHUTE.

HENRY S. CARHART AND HORATIO N. CHUTE.

PREFACE.

DURING the past decade the teaching of Physics in high schools and universities has undergone radical revision. The time-honored recitation method has gone out and the laboratory method has come in. As a natural reaction from the old régime, in which the teacher did everything, including the thinking, came the method of original discovery; the textbook was discarded and the pupil was set to rediscovering the laws of Physics. Time has shown the fallacy of such a method, and the successful teacher, while retaining all that is good in the new method, has already discovered the necessity of a clearly formulated, well digested statement of facts, a scientific confession of faith, in which the learner is to be thoroughly grounded before essaying to explore for himself. The maxim, "That only is knowledge which the pupil has reached as the result of experiment," has been found to have its limitations. With no previous instruction, the young student comes to the work without any ideas touching what he is expected to see, with entire ignorance of methods of experiment, and without skill in manipulation. He has no training in drawing conclusions from his own experiments. He is not a skilled investigator, and will be apt to discover little beyond his own ignorance, a result, it must be confessed, not entirely without value. Before the pupil is in any degree

fit to investigate a subject experimentally, he must have a clearly defined idea of what he is doing, an outfit of principles and data to guide him, and a good degree of skill in conducting an investigation.

A few years ago it seemed necessary to urge upon teachers the adoption of laboratory methods to illustrate the textbook; in not a few instances it would now seem almost necessary to urge the use of a text-book to render intelligible the chaotic work of the laboratory.

With this view of the situation, the authors have prepared this book for the class-room, as distinguished from a manual for the laboratory. The experiments described are, for the most part, designed to illustrate principles. They are, in other words, qualitative rather than quantitative in character. The attempt to combine both characters in one book has not, in our judgment, proved a success in the past.

In the preparation of this book the aim has been to formulate clear statements of laws and principles; to illustrate them amply, both by simple experiments and by appropriate problems; and to observe a logical order and sequence of topics, so that the pupil may pass from subject to subject with the aid and momentum of what he has already acquired.

The arrangement is such that a convenient division of the book either into two or three parts, corresponding to two or three terms in the school year, may be easily made.

Every experiment, definition, and statement of principle is the result of practical experience in teaching classes of various grades. Many of the illustrations are new, having been made from original drawings or from photographs of the actual apparatus set up for the purpose,

We should recommend teachers to supplement the classwork in this book with practical work in the laboratory. It is not necessary that the pupil should traverse the entire subject of Physics before taking up laboratory practice, but he should be kept in his class-work well ahead of the subjects forming the basis of his laboratory experiments.

An entire year should be devoted to the subject, and great advantage will be found in delaying its introduction till the student has acquired some knowledge of algebra and geometry.

ANN ARBOR, MICHIGAN.

H. S. C.

H. N. C.