LUCRETIUS AND THE ATOMIC THEORY 213 



not explain light, gravitation, and analogous phenomena, for 

 which a second kind of very subtle matter is required ; but this 

 may be supposed to consist of almost infinitely finer atoms. If 

 the molecules of gross matter be supposed constructed from 

 these finer atoms moving in certain special ways, this doctrine 

 would be in accordance with that of Lucretius, and would differ 

 little from the fluid theory, except that it would admit a void. 

 Thus far the displacement school. 



Those who believe in force exerted at a distance without a 

 means of communication have more elbow-room. They may 

 assume attractive and repelling forces, perhaps oblique and 

 tangential forces ; they may assume that these forces vary 

 according to laws, simple or very complex ; they may wholly 

 deny the existence of anything but force, and grant extension 

 and inertia to a field of force regulated in a special fashion. This 

 little field of force, or a combination of such fields, may build 

 their chemical atom, and the motions of these atoms, in their 

 turn as above, produce some of the properties or accidents of 

 gross matter ; they may believe in a plenum or a partial vacuum, 

 and in one or more kinds of matter, precisely as the other school 

 may do ; and, indeed, it is impossible to set a limit to their con- 

 jectures ; because when once the mind admits this conception 

 of an abstract force, such as that of gravitation as popularly 

 understood, it will not refuse to entertain the idea of any other 

 kind of force varying according to infinitely different laws, nor 

 is there any mental limit to the possible set of co-existent 

 forces. 



Let each party try. Mathematics provide a sure test of suc- 

 cess, though impotent to suggest a theory. The existence of 

 the chemical atom, already quite a complex little world, seems 

 very probable, and the description of the Lucre tian atom is won- 

 derfully applicable to it. We are not wholly without hope that 

 the real weight of each such atom may some day be known, not 

 merely the relative weight of the several atoms, but the number 

 in a given volume of any material ; that the form and motion of 

 the parts of each atom, and the distance by which they are sepa- 

 rated, may be calculated ; that the motions by which they 

 produce heat, electricity, and light may be illustrated by exact 

 geometrical diagrams ; and that the fundamental properties of 



