56 THE LIMITATIONS OF SCIENCE 



lead us, there has been a tendency of late years to avoid 

 them altogether. But while this method is the safer one 

 and provides us with a set of correct formulae and laws, 

 yet we are compelled to introduce into these equations 

 unknown terms, called coefficients, which express the 

 individual properties of different kinds of ponderable 

 bodies. For example, the same magnetic force pro- 

 duces different magnetic effects in iron and copper. If 

 we wish to obtain a deeper insight into the properties of 

 matter, he says, we must not be satisfied with simply 

 introducing for each substance its special coefficient, 

 whose value is to be determined by experiment; we 

 must invent some hypothesis about the mechanism of 

 matter which causes such differences of behavior. It 

 is this necessity which has led us to the hypothesis of 

 the electron. He then defines these electrons as ex- 

 tremely small particles, charged with electricity, and 

 present in immense numbers in all ponderable bodies. 

 They are of two kinds, positive and negative, and are 

 free to move in conductors of electricity and bound 

 to points of equilibrium in non-conductors. Sometimes 

 he considers them to be rigid, and at other times as 

 deformable bodies. Their inertia, or mass, is, for the 

 most part, an effect of their electric charge, and the 

 negative electron is probably free electricity without 

 ponderable mass. Professor Lorentz assigns no 

 specific properties to the ether, but he is required to 

 assume that it can penetrate freely all parts of the 



