TENDENCIES OF MODERN PHYSICS 65 



effect of electricity is called, becomes proportionately 

 greater and greater. Continue this process indefinitely, 

 and at last all the matter is gone, and there remains a 

 free electric charge, an immaterial point of electricity, 

 moving and possessing inertia or mass. And just here 

 lies the greatest danger of all such hypothesis a total 

 confusion of fact and fancy. In the first place, it is 

 not even based on experience, since the most rapidly 

 moving bodies of a sensible size have a velocity far 

 too little to make this effect noticeable. But, what 

 is more important, it is a method of thought to be used 

 with the utmost caution even in experimental processes. 

 The warning against such extra-polation is metaphor- 

 ically displayed in every physical laboratory. How we 

 would scorn the unscientific conclusions of the meta- 

 physicist who reasoned in the same way! Let us 

 imagine one saying that goodness is an attribute of 

 small, as well as of large men; now diminish the size 

 of a man and let his quality of goodness remain con- 

 stant, then we shall have an entity, concrete goodness, 

 left when the man shrinks to nothing. It is not neces- 

 sary to use such an absurd example, as a parallel case 

 exists in physical phenomena. A sphere, moving in 

 a fluid, experiences a like increase in apparent mass, 

 due to the necessity of imparting energy to the fluid. 

 Now decrease continually the density or mass of the 

 body and maintain its volume and velocity constant; 

 the hydrodynamic mass becomes proportionately 



