38 PHYSICAL SCIENCE 



experimental evidence to show that the mass of a 

 moving particle increases as its velocity approaches 

 that of light. Moreover, the principle of relativity 

 has changed profoundly our outlook on such 

 results as the conservation of matter and energy. 

 The concepts in which they are expressed are 

 relative to an observer and not absolute. We 

 may have unconsciously arranged the cards, and 

 then rediscovered with enthusiasm fours and 

 sequences put in by ourselves. 



Even if we assume that some reality underlies 

 phenomena, it is clear that the reality must be 

 very different from the mental picture which 

 common sense frames, when unaided by the in- 

 ductions of science. Our first conception of a 

 wooden stick involves the ideas of a certain lonof- 

 shaped form, of hardness, of weight, of a colour 

 more or less brown, perhaps of some amount of 

 elasticity. Examination with a microscope re- 

 veals many appearances invisible with the unaided 

 eye, and we find that the stick has a structure 

 much more detailed than we imagined. From the 

 results of observation and experiment, physics 

 teaches us that the properties of the stick can 

 only satisfactorily be represented by the hypothesis 

 that the substance of it is divisible, but not in- 

 finitely divisible ; that it consists of discontinuous 

 particles or molecules. Again, chemistry assures 

 us that the molecules of the stick are made up of 

 still smaller parts or atoms, which separate from 

 each other when chemical action occurs, when, for 

 instance, the stick is burnt, and can afterwards 

 rearranofe themselves into new molecules. 



When we pursue our inquiries into the nature 



