418 SKETCHES OF CREATION. 



tion requires. Since 1789, its period has shortened two 

 days and sixteen hours. Similar retardation — resulting in 

 a similarly accelerated angular velocity — has been fully es- 

 tablished in the cases of the comets of Brorsen, Faye, and 

 D' Arrest. 



The only explanation that has ever been offered of these 

 exceptional phenomena is the assumption of the existence 

 of an all-pervading resisting medium commonly called 

 ether. Since the undulatory theory of light became estab- 

 lished, the existence of such a medium has been recognized 

 as necessary, and its presence has been assumed throughout 

 all those realms of space to which light has penetrated. 



A belief in the existence of an all-pervading ether is 

 much more ancient than the observations which have made 

 it a scientific datum. In the astronomy of the Brahmins, 

 the stars are said to swim in ether, as fishes in the water. 

 Kepler supposed comets to be native inhabitants of this 

 ethereal medium, like fishes in the sea. The Cartesian doc- 

 trine of " vortices" presupposes an all-pervading material 

 fluid. The existence of such a fluid was admitted by New- 

 ton ; and he demonstrates that its tenuity must be greater 

 than that of our atmosphere at the distance of two hundred 

 miles from the earth. In more recent times this doctrine 

 has been maintained or admitted by Whewell, Sir John 

 Herschel, Thompson, Mayer, Littrow, Helmholtz, Grove, 

 Tyndal, Watson, McCosh, Comte, Rorison, and, in short, by 

 every physicist who has investigated the subject. 



We are compelled, then, to assume the position that a re- 

 sisting fluid permeates space, and that the heavenly bodies 

 do not move in a vacuum. The consequences of this ad- 

 mission are stupendous beyond conception. Laplace dem- 

 onstrated that if the planetary bodies are solid, and if they 

 move in vacuo, their mutual perturbations, in long cycles, 

 compensate each other, and the stability of the solar sys- 



