vi PREFACE. 



mathematical strictness, and often by the help of tech- 

 nically mathematical methods. These characteristics 

 of the study of physics give to it a value, as a 

 means of training in habits of exact thinking, which 

 probably no other study possesses in the same degree, 

 but at the same time they make this study more than 

 usually difficult, especially to beginners. The conse- 

 quence is, that many students of elementary physics 

 never succeed in gaining any really valuable acquain- 

 tance with the subject. They may retain general 

 impressions of the results of some of the experiments 

 they have witnessed, but they do not get exact concep- 

 tions which can cast light upon each other and grow 

 within the mind ; or they may possibly remember 

 the words in which some of the general conclusions 

 of the science can be stated, though without having 

 any comprehension of what the real evidence for these 

 conclusions is, or of the reasoning by which they are 

 established: in short, what little is retained, in rela- 

 tion either to the experimental facts or to the laws 

 of physics, is kept in mind by a pure effort of memory, 

 in which the intelligence has no perceptible share. 



It is probable that the frequency, with which results 

 such as these attend the teaching of the fundamental 

 parts of physics, has furnished one of the motives that 

 have induced some authors and teachers to try to 

 arrange this subject in a series of consecutive proposi- 

 tions set forth in a manner imitated from Euclid's 

 Elements. It has, no doubt, been hoped that in this 



