654 ADDRESS OF PROFESSOR LOVERING. 
at the advanced age of threescore years and ten. Challis be- 
lieves that there is sufficient evidence for the existence of ether 
and atomsas physical realities. He then proceeds to say :—‘ The 
fundamental and only admissible idea of force is that of pressure, 
exerted either actively by the ether against the surface of the 
atoms, or as reaction of the atoms on the ether by resistance to 
that pressure. The principle of deriving fundamental physical 
conceptions from the indications of the senses does not admit of 
regarding gravity, or any other force varying with distance, as an 
essential quality of matter, because, according to that principle, 
we must, in seeking for the simplest idea of physical force, have 
regard to the sense of touch. Now, by this sense, we obtain a 
perception of force as pressure, distinct and unique, and not in- 
volving the variable element of distance, which enters into the 
perception of force as derived from the sense of sight alone. 
Thus, on the ground of simplicity as well as of distinct percepti- 
bility, the fundamental idea of force is pressure.” As a other 
matter is passive except when acted upon by the ether, the ether 
itself, in its quiescent state, must have uniform density. It must 
be coextensive with the vast regions in which material force 18 
displayed. Challis had prepared himself for the elucidation and 
defence of his dynamical theory by a profound study of the laws 
of motion in elastic fluids. From the mathematical forms IM 
which he has expressed these laws he has attempted to derive u 
principal experimental results in light, heat, gravitation, electricity, 
and magnetism. Some may think that Mr. Challis has done 
nothing but clothe his theory in the cast off garments of an oh 
lete philosophy. If its dress is old, it walks upon new legs- i” 
interplay between ether and atoms is now brought on to the m 
not as a speculation supported by metaphysical and theologi 
arguments, but as a physical reality with mathematical supports: 
I should do great injustice to this author if I left the impression 
that he himself claimed to have covered the whole ground of his 
system by proof. Mathematical difficulties prevented him Oe 
: ‘ e of 
reaching a numerical value for the resultant action of & Wav 
ether upon the atom. What he has written is the guidepoth 
pointing the direction in which science is next to travel : ages 
end of the journey is yet a great way off. The repeated P we bis 
of Mr. Challis against the popular physics of the day; and 
bold proclamation of the native, independent motion of the «77? 
5 
