122 BRUSH— DISCUSSION OF [April 24. 



late is that some or much of the ether's intrinsic energy is kinetic 

 and consists of some sort of wave motion or energy flux, whereby 

 a disturbance at any point in the free ether is ultimately felt every- 

 where else, diminishing in intensity, of course, with the inverse 

 square of distance from the seat of disturbance. 



It is not difficult to conceive of kinetic energy in the ether quite 

 apart from matter. Radiation is one form of such energy, and when 

 once launched in the ether it is persistent and quite independent of 

 its source. Interstellar space is alive with wave energy radiated 

 from countless suns, and at points far removed from any single sun 

 this energy is approximately isotropic. Of course this known iso- 

 tropic wave energy in the ether of space is far too feeble to play 

 any appreciable part in gravitation, and I call attention to it only for 

 the purpose of showing that one sort of free isotropic wave energy 

 in or of the ether in celestial space is already a known phenomenon. 



Probably the ether waves concerned in gravitation are not the 

 transverse kind known to us, though it is not difficult to think of 

 transverse waves of great amplitude, embodying great energy, and 

 of such great length that they pass freely through all bodies without 

 appreciably heating them — even electrical conductors. (Incidentally, 

 we cannot be sure that the intrinsic energy of the ether does not 

 impart some low degree of temperature to matter, because we know 

 of nothing in nature at the absolute zero of temperature or any- 

 where near it.) It seems more likely, however, that the ether waves 

 of gravitation are longitudinal, or otherwise consist in an energy flux 

 which, by reason of its universal presence, has not been made mani- 

 fest except by gravitation. 



It is easy to understand how the supposed spherical field of influ- 

 ence, or energy shadow, surrounding any body of matter may be 

 initiated, but just how it is maintained may never be known; though 

 I hope to have something to say in this connection in a future dis- 

 cussion. But that the field of influence actually is maintained seems 

 certain ; gravitation itself is a demonstration of it. 



The simplest mental picture of the supposed field of influence 

 which I can think of is a spherical energy shadow, and I have en- 

 deavored to make this conception visible in Figs. 2 and 3 as light 



