Dynamical Theories of Gravitation, 159 



no opinion. The bases of them are nevertheless quite un- 

 altered, and therefore open to the same objections ; namely, 

 he sets himself in contradiction with the principle of the 

 conservation of energy, which, moreover, Dr. Bock himself 

 admits. 



Hamburg, 1894. 



Appekdix (added Jan. 1895). — All who have thought on the 

 subject know that, in the case of a falling body, the motion gene- 

 rated comes from the aether, according to any dynamical explana- 

 tion of gravitation : and when the body strikes the earth's surface, 

 shaking its molecules into vibration by the concussion, these 

 ("heat") vibrations develop waves in the aether, or are "radiated" 

 away. So we have a cyclical process here, where motion passes 

 from a material agent and back again to that agent, in a circle. 



In accordance with the above we see, then, that stars or 

 stellar suns do not " pour their heat unrequited into space/' but 

 return their stores of motion to the source whence they were 

 obtained. For if gravity be caused by a material agent, and if 

 solar energy be derived from gravity, then manifestly solar energy 

 is returning only to its original source, to be again available for 

 generating heat (through gravitation) in some other regions of 

 the universe. 



Evidently, if chemical action be caused by a material medium, then 

 an animal or a steam-engine lifting a weight is an instance (again) 

 of motion coming from a material substance, and going back to it 

 in a circle at the same time. A locomotive, as we know, converts 

 all its energy into heat (which is radiated into the aether) as it 

 progresses with its train : so clearly we have the cyclical process 

 of exchange of motion again here : the same being true of work 

 derived from falling water (cataracts) or from winds. If, finally, 

 one pure speculation be permitted, we might suggest that over- 

 grown stars may, towards their centres, become from excessive 

 compression inadequately penetrable by the atoms of the aethereal 

 gas, and so the overgrown masses be broken up by conversion 

 of the aethereal motion into heat. Thus cyclical change would 

 apply to the Universe generally : the stellar bodies constituting in 

 sum a gigantic grained gas inside an excessively fine atomic one. 

 For the tentative development of this idea, a paper in the 

 Philosophical Magazine, August 1879, also Sitzungsberichte, April 

 1883, Vienna, may be mentioned. So it appears that the Universe 

 may at present (in the same sense as a gas is) be in equilibrium of 

 temperature. 



