64 THE LIMITATIONS OF SCIENCE 



the periodic disturbances produced in the plenum by the 

 oscillatory motions of the same particles about fixed 

 centers. These are said to be useful ideas and clear 

 explanations. But are they? Have we accomplished 

 anything more than to reaffirm the statement that a 

 current of electricity under certain conditions flows 

 through a wire, when we say a stream of charged par- 

 ticles moves through the wire? In the first place, we 

 create the particles, and next endow them with an 

 occult power of motion. Again, when zinc and cop- 

 per are placed in contact and separated, the zinc be- 

 comes positively charged with electricity, the copper 

 with negative, and the two attract each other. Do we 

 learn anything more when we affirm that an excess of 

 positive electrical particles passes into the zinc and 

 negative ones into the copper ? Why should they act so ? 

 In both cases we have merely stated an unknowable 

 cause in different words. The law remains the same 

 whether we say electricity or electrical particle, and 

 the former term expresses less pretense of knowledge. 

 Far more significant, and less justifiable even, is the 

 attempt to explain the mass of a body as an attribute of 

 lectricity. Mathematical analysis shows that an elec- 

 trically charged body, moving with great velocity, has 

 a resistance to motion apparently greater than when 

 not so charged. Now, they say, continually diminish 

 the ponderable mass of the body and maintain the elec- 

 tric charge constant ; the electro-magnetic mass, as this 



