ADDRESS OF PROFESSOR LOVERING. 655 
have aroused criticism. What prevents the free ether, asks the 
late Sir John Herschel, from expanding into infinite space? Mr. 
Challis replies that we know nothing about infinite space or what 
happens there, but the existence of the ether, where our experi- 
ence can follow it, is a physical reality. The source of the mo- 
tion which the ether acquires is not the sun: for the most efficient 
cause of solar radiation is gravitation and condensation. Our 
author avoids the vicious circle of making gravitation, first the 
reason and afterwards the consequence of the motion of the ether. 
He says: “It follows that the sun’s heat, and the heat of masses 
in general, are stable quantities, oscillating, it may be, like the 
planetary motions, about mean values, but never permanently 
changing, so long as the Upholder of the universe conserves the . 
force of the ether and the qualities of the atoms. There is no law 
of destructibility : but the same Will that conserves can in a mo- 
ment destroy.” The following remarks upon this theory deserve 
our attention. The explanation of any action between distant 
ies by means of a clearly conceivable process, going on in the 
intervening medium, is an achievement of the highest scientific 
value. Of all such actions that of gravitation is the most univer- 
sal and the most mysterious. Whatever theory of the constitu- 
tion of bodies holds out a prospect of the ultimate explanation of 
the process by which gravitation is effected, men of science will 
be found read y to devote the whole remainder of their lives to the 
development of that theory.” 
the hypotheses of Challis and Le Sage have one thing in com- 
_ Mon; the motion of the ether and the driving storm of atoms 
_ Must come from outside the world of stars. ‘On either theory, 
the universe is not even temporarily automatic, but must be fed 
_ om moment to moment by an agency external to itself.” Our 
= Science is not a finality. The material order which we are said to 
a ‘now makes heavy drafts upon an older or remoter one, and that 
Again upon a third. The world, as science looks at it, is not self- 
“ustaining. We may abandon the hope of explaining gravitation, 
And make attraction itself the primordial cause. Our refuge 
‘Sin the sun. When we qualify the conservation of energy by 
: the dissipation of energy, the last of which is as much an induc- 
“on of science as the first, the material fabric which we have 
. ‘Constructed still demands outward support. Thomson calculates 
that, within the historical period, the sun has emitted hundreds of 
