The purpose of this manual is to teach some of the principles of physics that ore commonly applied in things about us, and in such a way that the study shall be a training in observation and thinking. It may be used in courses where the important object is to afford such training, or in courses where its function is mainly to illustrate the subjects studied. To secure the first of these objects, the matter has been so arranged that the student shall have been prepared for each exercise by the work preceding it; and the exercise, drawing upon this knowledge, will add to it a single fact or principle by demonstrating its operation and by suggestive questioning. The same exercises may serve also the second purpose, and many of them show directly the application of principles in things about us.<br><br>In general, the material to be used is simple and not costly. Such material often serves best, because it divests the operation of strange or unusual features and directs the attention rather to the thing shown than to the method of showing it.<br><br>The manner of using this set of exercises may, of course, be adapted to the desires of the teacher and the facilities at hand.