X PREFACE. 



alone the true import and mutual bearing of these facts 

 can be discovered and expressed. The student who 

 wishes to advance beyond the mere rudiments of the 

 subject will inevitably find himself obliged to give at 

 least as much attention to the mathematical as to the 

 experimental side of it ; but I think there can be little 

 doubt that it is best for him to begin by studying 

 separately experimental physics and pure mathematics, 

 and not to encounter at first the combination of the 

 difficulties of both subjects which the mathematical 

 treatment of physics presents. If once he has acquired 

 clear conceptions of the fundamental physical truths, 

 and also the requisite familiarity with the methods of 

 pure mathematics, he will find very little difficulty in 

 bringing his mathematical knowledge to bear upon 

 physical problems. 



Hitherto, however, it has been very difficult for a 

 teacher, even when thoroughly convinced of the impor- 

 tance of making the first instruction in physics as 

 thoroughly practical as possible, to carry his views into 

 practice ; he has derived little or no assistance from 

 the existing text-books of physics ; and, unless he has 

 been able not only to devise a general plan of instruc- 

 tion, but also to contrive every detail of the experimental 

 work he gave his pupils to do, he has had no choice but 

 to fall back upon the usual plan of reading a text-book, 

 or at best of showing experiments with ready-made 

 apparatus. But now all who wish to adopt a more 

 satisfactory system have an excellent guide offered to 



