VI PREFACE AND INTRODUCTION. 



The authors feel that the appendices (a) on Terrestrial Magnet- 

 ism, () on Ship's Magnetism and the Compensation of the 

 Compass, (r) on Miscellaneous Phenomena, and (d] on Miscel- 

 laneous Practical Applications will appeal to nearly every one 

 who has occasion to use this book. Every student should know 

 something about these various subjects but most of this material 

 should be omitted from a first systematic study of the Elements 

 of Electricity and Magnetism. The appendix on Ship's Magnet- 

 ism and the Compensation of the Compass especially is recom- 

 mended to those who wish to gain a clear insight into the physics 

 of this subject. 



1 Following the plan of our Elements of Mechanics, we wish to 

 include an introduction in this text. What needs to be said in 

 introduction, however, is very brief, assuming that the student 

 has read the introduction to our Mechanics. There seems to be 

 among our students a general indifference towards rational 

 physics study. What does this mean ? That all students are 

 unworthy, or that physical science is at fault? Neither. It seems 

 to us that this indifference is due to a misunderstanding, and we 

 believe that it may be made powerless to deter the student from 

 a reasonable expenditure of effort in the rational study of the 

 physical sciences if young men be led to understand what kind of 

 interest they may be expected to have in such study. Gilbert 

 Chesterton, in his essays on Heretics, says, very wisely, that the 

 only spiritual or philosophical objection to steam engines is not 

 that men pay for them or work at them or make them very ugly ; 

 or even that men are killed by them ; but merely that men do not 

 play at them. This is precisely the objection to physical science. 

 Men do not play at it, or, when they do, -it is play in the weakest 

 and most contemptible sense of the word. Physical science in 

 its elements is detached from the more intensely human interests, 

 and the will alone can determine its pursuit. 



THE AUTHORS. 



March 22, 1908. 



