June 5, 1914] 



SCIENCE 



837 



mined in this work with an error which does not 

 exceed one per cent. The value found is in very- 

 close agreement with that obtained by other 

 methods. It is probable, however, that none of 

 these other methods are capable of as high a pre- 

 cision as the photo-electric method here used. 



The discovery that an electron ejected from a 

 body under the influence of mono-chromatic light 

 acts as though the whole energy content of the 

 light wave were transferred without loss to the 

 electron has important bearing on the whole 

 framework of theoretical physics. It constitutes 

 a new triumph of Planck's atomistic theory of 

 radiation or, better, perhaps, a new proof of the 

 usefulness in a new domain of Planck's "h." 



The full theoretical significance of the mass of 

 facts connected with "h" which have come to light 

 within the past three or four years has not, how- 

 ever, as yet been fully discerned. 

 Discussion of " A Kinetic Theory of Gravitation" 

 — (1) Gravitation is Due to Intrinsic Energy 

 of the Ether; (2) Transmission of Gravitation 

 can not ie Instantaneous: Charles F. Betjsh. 

 A kinetic theory of gravitation was outlined by 

 the author at the Minneapolis meeting of The 

 American Association for the Advancement of 

 Science,! in which the ether is assunaed to be en- 

 dowed with vast intrinsic kinetic energy in wave 

 form of some sort capable of motive action on 

 particles, atoms or molecules of matter, and prop- 

 agated in every conceivable direction so that the 

 wave energy is isotropic. Particles or atoms are 

 imagined to be continually buffeted in all direc- 

 tions by the ether waves like particles of a pre- 

 cipitate suspended in turbulent water. There are 

 no collisions because neighboring particles follow 

 very nearly parallel paths. Each atom or particle 

 is regarded as a center of activity due to its 

 energy of translation initially derived from the 

 ether; whereby it has a field of influence extend- 

 ing in all directions, or casts a spherical energy 

 shadow, so to speak. The energy shadow of a body 

 of matter is the sum of the shadows of its constitu- 

 ent parts. The energy shadows of two gravitating 

 bodies interblend, so that the energy density be- 

 tween them is less than elsewhere, and they are 

 pushed toward each other by the superior energy 

 density or wave pressure, on the sides turned 

 away from each other. 



In the present discussion the author employs 



some impressive illustrations to show that the 



energy acquired by falling bodies has some ex- 



1 Science, March 10, 1911; Nature, March 23, 



1911. 



ternal source, and that it must be ethereal energy 

 or energy of space; and he holds that the term 

 "potential energy of position," as applied to a 

 system of gravitating bodies implies the energy- 

 endowed ether as a necessary part of the system. 

 As a corollary, the author explains how bodies 

 falling toward each other by reason of their mu- 

 tual attraction, and thus accelerating, that is to 

 say, absorbing energy from the ether, can not 

 rigidly obey Newton's law of inverse squares of 

 distance. The force of attraction iustead of vary- 

 ing as 1/D-, as it does for bodies at rest or in uni- 

 form motion, varies as 1D(2— ^) for bodies acceler- 

 ating in the line of attraction, wherein a; is a very 

 small quantity which appears to vary with the rate 

 of energy transformation or velocity of fall. 

 When acceleration is negative, that is to say when 

 energy transformation is from the accelerating 

 body to the ether, x becomes positive. 



In the ease of a planet of the solar system, x 

 obviously increases in importance with eccentri- 

 city of orbit, and may become appreciable in the 

 highly excentric orbit of Mercury. The au- 

 thor expresses the hope that this alternately plus 

 and minus deviation from Newton's law will be 

 found adequate to explain the secular advance of 

 the perihelion of Mercury's orbit. He also calls 

 attention to the fact that the moon moves toward 

 and away from the sun almost the whole diam- 

 eter of her orbit every month, and hopes that, in 

 this connection, the deviation from Newton's law 

 above indicated may explain the outstanding lunar 

 perturbations, and perhaps cancel another to be 

 mentioned later. 



In the second division of the paper the author 

 describes the premises from which Laplace drew 

 his famous conclusion that gravitation is trans- 

 mitted with infinite, or virtually infinite, velocity; 

 a dogma which ' ' for more than a century has 

 blocked the path of fruitful thought on the phys- 

 ics of gravitation. ' ' The radically different prem- 

 ises growing out of the theory under discussion 

 are then described and contrasted with those of 

 Laplace, to explain why and how the author 

 reaches such a widely different conclusion. He 

 concludes that, even if the velocity of transmis- 

 sion is no greater than that of light, the moon's 

 mean motion will be retarded a very few seconds 

 of arc only, in a century; and the retardation will 

 be correspondingly less if the velocity is greater 

 than that of light. This retardation, of course, 

 adds to the unexplained acceleration, if any, of the 

 moon's motion; but the author further hopes that 

 this retardation, plus the outstanding acceleration, 



