TO THE TEACHER 



IN this book will be found an unusual number of prob 

 lems. It is not intended that each member of each 

 class shall work all of the problems. It is hoped that 

 they are sufficiently numerous and varied to enable you 

 to select what you need for your particular class. No 

 author can make a comfortable Procrustean bedstead. 



You would do well to secure, in the fall of the year, a 

 supply of the pith of elder or sunflower stalk, and several 

 full-blown thistle-heads, that they may be well dried and 

 ready for experiments in electricity during the dry, cold 

 weather of winter. 



The author would be glad to receive any suggestions 

 from any of his fellow-teachers who may use this book, or 

 to answer any inquiries concerning the study or apparatus. 



Most of the apparatus mentioned in this book may 

 be obtained from E. S. RITCHIE & SONS, Boston, or of 

 JAMES W. QUEEK & Co., Philadelphia. 



The author has prepared a Teacher's Hand-Book to 

 accompany this volume, with answers to the problems, 

 and much additional matter of interest to teachers of 

 Natural Philosophy. 



