MINUTES. xvii 



by means of a rotary molecular vibration. To this end we may sup- 

 pose that ether is in a state of continual special vibration determining 

 its tension, and that this vibration is decreased by its passage through 

 the molecular interstices of the matter. The contrary might, how- 

 ever, be supposed, and this would appear more plausible, viz., that 

 the phenomenon is caused by the vibration of the atoms composing 

 the matter, and that the tension of the outside ether is transformed 

 by the molecular vibration of the bodies. This seems to me the more 

 plausible opinion." 



In neither his ether-absorption theory nor his alternative hypoth- 

 eses does Gregorio explain how the supposed diminution of ether 

 pressure outside bodies of matter is maintained after absorption of 

 ether has ceased : and indeed this seems to me impossible of explana- 

 tion. Nor does he offer any suggestion of the source of the energy 

 acquired by falling bodies. 



My own " Kinetic Theory of Gravitation," ^ put forth in Decem- 

 ber, 1910, is based on two fundamental concepts of the ether of space : 

 First, that the ether is endowed with vast intrinsic energy — energy 

 quite apart from matter — free energy. This was then and is now the 

 belief of many eminent physicists. Second, that some, perhaps all, 

 of the ether's intrinsic energy exists in wave form of some sort capa- 

 ble of motive action on matter, and propagated in every conceivable 

 direction, so that the wave energy, or energy flux, is isotropic ; and 

 whereby a disturbance of any kind, anywhere in the ether, is in due 

 time felt everywhere else, the intensity of disturbance diminishing 

 with the inverse square of distance from its seat. 



The last concept above I believe to be original with me. I find 

 nothing of it in Gregorio's paper, but it is essential to my theory. 



In his more recent paper, 1914, Gregorio reaffirms his 1892 theory 

 of ether pressure and ether absorption by matter, and seeks to " de- 

 velop my idea further " in the light of more recent discoveries in 

 physics. He now regards the ether as a " dynamic fluid " composed 

 of " imponderable particles, extremely minute, of the condensed fluid 

 itself," which he calls " superatoms." He says further that " the 

 actions of magnetic and electric currents " clearly prove " that an 

 imponderable fluid can generate energy and, as it were, transform 

 itself into energy." . . . 



Again I find nothing of the second, and essential, postulate of my 



own theory. 



Charles F. Brush. 



Cleveland, 



November, 1922. 



'^Science, March 10, 1911 ; Nature, Marcli 23, 1911 ; Proc. Amer. Phil. Soc, 

 Vol. LIII., No. 213, Jan.-May, 1914; Proc. Amer. Phil. Soc, Vol. LX., No. 

 2, 1921. 



