16 PROCEEDINGS OF THE AMERICAN ACADEMY. 



It is with some diffidence that this paper attempts to reconcile the facts 

 with any hypothesis, for hypotheses sometimes lead to dangerous delu- 

 sions. If, however, one never forgets the essential difference between 

 fact and hypothetical inference, a theory may afford useful suggestions 

 for further research. The facts under discussion in the present paper 

 seem to me to be adequately connected by none of the current concep- 

 tions concerning atoms, hence it has seemed not wholly pointless to 

 postulate a theory which might serve better. The essential elements of 

 this theory must be evident from the trend of the hypothetical discussion 

 above ; they are not wholly new. Since changes of atomic volume seem 

 to be so closely associated with the most intimate properties of substance, 

 it seems necessary to assign more importance to the atomic " sphere of 

 influence " or the " free space " around the atomic centres than is cus- 

 tomary. Indeed, the properties of material seem to be as much concerned 

 with the " atomic shell " as with the " atomic centre." The two hypothet- 

 ical conceptions are so closely related as to be inseparable. 



Such a point of view leads to the conception of an atom as a compres- 

 sible field of force possessing two attractive attributes, chemical affinity 

 and gravitation, both of which may be concerned in chemical action. 

 Mass may be supposed to be causally connected with gravitation. The 

 fact that in many cases affinity diminishes with increasing atomic weight,* 

 taken together with the Laws of Faraday and of Dulong and Petit, 

 suggests that the two attractive forces in the atom may bear some 

 sort of reciprocal or additive relationship to one another, — that the 

 product or sum of the two may afford a constant basis for the vibrations 

 of heat and electricity. This relation is often hidden by electrical attrac- 

 tion, which plays so important a role in chemical action that it is some- 

 times hard to distinguish the intensity of chemical affinity proper. In 

 such an atom one can imagine that either thermal or electrical vibration 

 might cause distention. The phenomena of electricity suggest that 

 electricity plays around the atomic surface, while heat seems to be 

 concerned with a more fundamental or central agitation. Light-vibra- 

 tion, which seems also to be intimately concerned with atomic structure, 

 would be assumed to be a surface effect like electrical vibration. 



Such an atom would be compressible under the influence of its own 

 affinities as well as under the influence of external pressure. Permanent 



* Van't Hoff, Vorl. th. phys. Chem., III. 87 (1900). Compare also the relation 

 of the energy-quotients of similar metals referred to on p. 10 of the present 

 paper. 



