PREFACE. 



This manual consists of a series of tests on direct and alter- 

 nating current apparatus, selected with reference to their practical 

 usefulness and instructive value. While the book has been pre- 

 pared primarily for students, it is hoped that it may prove helpful 

 to others. The presentation is in the form of a laboratory 

 manual; the author, however, has not restricted himself to a 

 mere statement of instructions for conducting tests but has 

 directed the reader's attention to the principles that underlie the 

 various experiments and to the significance of the results. Ex- 

 perience has shown that theory is more readily grasped when it is 

 thus combined with its application and that the application is 

 more intelligently made when its broader bearings are understood. 

 The material has been systematically arranged and it is believed 

 that the book may be found useful for reference or as a text, 

 aside from its use in testing. 



From the text proper are excluded specialized tests and those 

 that are of limited application or require unusual testing facili- 

 ties, such tests being described in the appendices to the several 

 experiments. These appendices thus permit a fuller discussion 

 of some of the details of the tests and various modifications than 

 could be included to advantage in the text proper. The tests in 

 general are those that can be performed in any college laboratory. 



No attempt has been made to make the work exhaustive or 

 complete ; on the contrary every effort has been made to eliminate 

 matter of secondary importance and that which is of questionable 

 technical or pedagogical value. 



The aim has been to arrange an introductory series of experi- 

 ments of a comprehensive nature, so that in a reasonable time 

 and with a reasonable amount of effort the student may acquire 



