tions, he surrenders the apparatus to another who may be ready to use it, and next occupies himself in writing up the results of his experiments in his note-book. These note-books are deposited in a receptacle near the door as he leaves the laboratory. Nothing is ever written in them except at the times of experimenting. These books are examined by the teacher; they contain the only written tests to which the pupil is subjected, except the annual test given under the direction of the Board of Supervisors. Pupils, in general, are permitted to communicate with their teacher only. "Order, Heaven's first law," is absolutely indispensable to a proper concentration of thought and to successful work in the laboratory. Only in exceptional cases, such as work on specific gravity and electrical measurements, has it been found necessary to duplicate apparatus. The same apparatus may be kept on the desks through several exercises, or until every pupil has had an opportunity of using it. Ordinarily two pupils do not perform the same kind of experiment at the same time. With proper system, any teacher will find his labors lighter than under the old elaborate lecture system; and he will never have occasion to complain of a lack of interest on the part of his pupils. I I venture to hope, in view of the kind and generous reception given to the Elements of Physics, that this attempt to make the same methods available in a somewhat more elementary work may prove welcome and helpful. It has been my aim in the preparation of this book to adapt it to the requirements and facilities of the average high school. With this view, have endeavored to bring the subjects taught within the easy comprehension of the ordinary pupil of this grade, without attempting to "popularize" them by the use of loose and unscientific language or fanciful and misleading illustrations and analogies, which might leave much to be untaught in after time. Especially has it been my purpose to carefully guard against the introduction of any teachings not in harmony with the most modern conceptions of Physical Science. NOTE TO THE REVISED EDITION. WHILE the general plan and arrangement of the original edition of this work have been preserved in this revision, numerous changes dictated by experience and improved methods of presenting portions of this science have been made here and there throughout the text. The subjects of Electricity and Magnetism, however, have been entirely rewritten and made to conform in plan and arrangement to the treatment of the same subjects in my Principles of Physics. Although several new topics, for instance, Specific Heat, have been introduced, yet the volume of the text proper has been increased only sixteen pages. Aside from these changes and additions, the matter of the text remains the same. Several subjects treated in the text notably the Pendulum, Expansion Coefficients, the Dynamo, and the Electric Motor have been "continued" in the Appendix for the benefit of those who may wish to pursue these subjects further than a very elementary text-book will admit. I may be permitted to suggest that copies of the Principles of Physics, the style of which is naturally similar to the style of this book, but the treatment much fuller, if made accessible to both teacher and pupil, cannot fail to be very helpful to both. A. P. G. 1896. Dynamics of fluids. - Pressure in fluids. - Barometers. -Com- pressibility and elasticity of gases. - Buoyancy of fluids. - General dynamics. - Momentum, and its relation to force. - Three laws of motion. - Composition and resolution of forces. - Center of gravity. - Falling bodies. - Curvilinear motion. - Effects of heat. - Thermometry. — Convertibility of heat. - Batteries. Effects produced by electric current. Elec- - - rent and magnetic electric induction. · Dynamo-electric ma- Study of vibrations and waves. Sound-waves, veloc- ity of; reflection of; intensity of; reënforcement of; inter- ference of. Pitch. Vibration of strings. Overtones and Radiant energy, ether-waves, light. — Photometry. — Reflection of |