L PHILOSOPHICAL SOCIETY OF WASHINGTON. 
theory, have abundantly vindicated its value as an instrument of 
chemical research, while conspiring to vindicate its truth by giving 
to its votaries that ability of prediction which is the crucial test of 
science. The theory, besides, has sometimes “snatched a grace 
beyond the reach of art” by working retroactively to the purifica- 
tion of chemical method from errors and defects incident to the 
most careful manipulations of the practical chemist. 
Standing in the presence of chemical science, as now constituted, 
Baron Liebig has expressed the opinion that we can scarcely con- 
ceive how it could have been developed without the Daltonian 
hypothesis. And yet the atom of Dalton, considered in its rela- 
tion to our natural senses, is just as incapable of visible and tangi- 
ble demonstration as the atom of Democritus. For this reason it 
is known that Faraday could never fully reconcile himself to the 
modern doctrine of atoms.* But, in fact, there is a genetic and a 
generic difference between the ancient and the modern conception. 
The former is the offspring of the philosophical imagination 
toying with analogy. The latter is the offspring of the philosophi- 
cal imagination gendering with the homologies of reason. The atom 
of Democritus sprang into thought under the plastic forms by 
which he figured to himself at will the invisible relations and 
constitution of matter. The atom of Dalton sprang into thought 
from a rigid mathematical mind figuring to itself certain de- 
terminate relations which had become visible in elastic fluids. 
The atom of Democritus was, by the terms of its genesis, incapable 
of verification. The atom of Dalton was, by the terms of its 
genesis, capable of verification, if true, in all the gases of nature. 
Metaphysic thought born of the analogical reason can never con- 
clusively prove its legitimacy. Metaphysic thought born of the - 
homological reason can always prove its legitimacy, and, until it 
does, has no rights of heirship in the kingdom of science. The 
essential quality of a metaphysico-physical hypothesis is that it 
should be plausible; the essential quality of a physico-metaphysical 
hypothesis is that itshould be apodictic. The former is “magistral 
and peremptory;” the latter is “ingenuous and faithful.” The 
former is contrived in such sort as to be “soonest believed,” the 
* Faraday: Experimental Researches in Electricity, vol. 2, p. 284. But 
ef. vol. I, p. 249. . 
