38 THE LIMITATIONS OF SCIENCE 



tend invariably to express our abstract conclusions in a 

 more or less concrete form. We shall always speculate 

 about the manner of the propagation of light to the 

 earth from the sun, and it is convenient to express this 

 transfer of energy either as a periodic disturbance 

 taking place in something filling space or as something 

 projected through space. Such indefinite speculations 

 are simple enough and allow us to state all that we 

 need in order to assume continuity of action in free 

 space. The obscurity and confusion in the science of 

 optics arise from the attempts to express in detail the 

 nature of the waves or of the particles of light. A 

 method where speculation is kept to its lowest terms is 

 quite different from the prevalent custom of spending 

 the greater part of our effort on the fictitious proper- 

 ties of the ether rather than on the phenomena and 

 laws of matter. 



The problem of tracing the tendencies of thought 

 concealed in the conflicting data and opinions of the 

 present state of physics is difficult, and this difficulty 

 is increased by the unusual amount of new material 

 brought to light since the discovery of the X-rays by 

 Professor Roentgen in 1895. The phenomena con- 

 nected with the discharge of electricity through gases 

 and with radio-activity are obscure, and speculation 

 about them correspondingly bold. There is a desire, 

 quite common, to ignore the importance of the more 

 regular advance in other branches of physics and to 



