PROFESSOR LOVERING'S ADDRESS. 317 



to have covered the whole ground of his system by proof. Mathe- 

 matical difficulties prevented him from reaching a numerical value for 

 the resultant action of a wave of ether upon the atom. What he has 

 written is the guide-post, pointing the direction in which science is 

 next to travel ; but the end of the journey is yet a great way off. 

 The repeated protests of Mr. Challis against the popular physics of 

 the day, and his bold proclamation of the native, independent motion 

 of the ether, 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 experience 

 can follow it, is a physical reality. The source of the motion 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 afterward 

 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 quan- 

 tities, 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 moment destroy." The following remarks upon 

 this theory deserve our attention : " The explanation of any action 

 between distant bodies 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 

 universal 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 

 ready 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 common : 

 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 from moment to 

 moment by an agency external to itself." Our science is not a finality. 

 The material order which we are said to know 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-sustaining. We may abandon 

 the hope of explaining gravitation, and make attraction itself the pri- 

 mordial cause. Our refuge then is in the sun. When we qualify the 

 conservation of energy by the dissipation of energy, the last of w T hich 

 is as much an induction 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 hun- 

 dreds of times as much mechanical energy as is contained in the united 



