IOWA ACADEMY OF SCIENCES. 51 



The strain in each case extends to infinity, or as far as the 

 ether extends. If the displacement of ether were prevented 

 from extending on one side by a rigid imaginary wall, the 

 whole strain on that side would take place between the atom 

 and the wall, and would be more intense than on the opposite 

 side. The atom would tend to move in such direction as to 

 decrease the intensity of the strain, namely, from the wall if 

 the displacement were outward, toward the wall if the displace- 

 ment were inward. By the same reasoning two atoms repel 

 each other if the displacement is outward, and attract if it is 

 inward. The law of gravitation is thus explained on the 

 hypothesis that each atom is accompanied by an inward dis- 

 placement of the surrounding ether, proportional in amount to 

 the mass of the atom. 



Minchin (Statics, fourth edition, vol. 2, p. 475,) by a couise 

 of mathematical reasoning has reached the same conclusion. 



If the atoms be regarded as cavities, the mass of an atom is 

 represented by the quantity of ether removed, which repre- 

 sents also the volume of the atom. Since atomic volume is not 

 proportioned to atomic weight, the cavity- atom hypothesis 

 must be abandoned. 



On the condensation hypothesis the mass of an atom is the 

 quantity of ether condensed, its volume the space occupied on 

 the average by the condensed mass which may have any kind 

 of irregularity of form. 



This hypothesis implies that all atoms are built out of the 

 same original stuff, and is in this respect similar to but not 

 identical with Front's hypothesis. The fact that all atoms 

 attract with forces proportional to their masses shows that all 

 atoms possess the same kind of mass, and are therefore likely 

 to consist of the same sort of stuff. 



Valence, selective affinity, electric and other peculiarities of 

 atoms, must, if this hypothesis of gravitation be correct, find 

 their explanation in the form and density of the atom, the dis- 

 tribution of its stuff in space, which can be expressed as a 

 function of the three space co ordicates; together with the laws 

 of energy, which express the relations of the atom to the ether. 

 The field of force about an atom is also capable of representa 

 tion by a function of the space co-ordinates such that when the 

 distance r from the atom is relatively great the equipotential 

 surfaces are very nearly spheres. 



