PREFACE TO THE FIRST 

 EDITION 



In recent years we have witnessed a great 

 development of physical science. The different 

 sections into which natural knowledge is, for the 

 sake of convenience, divided, have grown each 

 within its own domain ; and, moreover, have 

 shown increasing signs of extending beyond the 

 boundaries arbitrarily traced between them. The 

 methods of physics, in the restricted sense of 

 that word, are being more and more applied to 

 chemical and biological problems, while many 

 questions in physics can only be investigated 

 by those with mathematical or chemical training. 



Thus it happens that an acquaintance with 

 the knowledge newly acquired in one department 

 of science is necessary for the study of another ; 

 indeed, the phenomena which need for their 

 interpretation the methods of two branches of 

 science have proved often the most fruitful field 

 of inquiry. 



For reasons such as these it has been 

 thought possible that a short account of some 

 of the important investigations now being carried 

 on in the physical laboratories of the world 

 might prove useful to students of science in 

 general ; while it is hoped that, by treating the 

 subject as far as possible without technical 

 language, the book may also appeal to those 



