382 



SCIENCE 



[N. S. Vol. XXXIII. No. 845 



is enormous; sufficient, if converted into heat, 

 to vaporize the most refractory falling body. 



We are here confronted with the question, 

 vehence comes the energy acquired by a falling 

 body? Certainly it was not inherent in the 

 body before the fall, as evidenced by the fact 

 that during unimpeded fall none of the phys- 

 ical or chemical attributes of the body, aside 

 from the acquired motion, changes in the 

 slightest degree. 



We have been taught that before the fall 

 the body was endowed with " potential energy 

 of position," which is converted into kinetic 

 energy during the fall. I think " energy of 

 position " is an unfortunate term because it 

 is so very inadequate. To me, it explains 

 nothing. The case is not like that of a flexed 

 spring, where there is internal molecular 

 strain or displacement. 



Let us imagine a pound-weight of iron, for 

 instance, raised from the surface of the earth 

 to a point near the moon, in a line joining the 

 centers of the two bodies, the point so chosen 

 that the opposing attraction of the earth and 

 the moon shall exactly balance each other, 

 leaving orbital motion out of consideration. 



On the surface of the earth the pound- 

 weight had some so-called "potential energy 

 of position " because it was capable of falling 

 into a pit; but in its new position near the 

 moon, this potential energy not only has not 

 been augmented, but has disappeared entirely; 

 the pound-weight, left free to move, remains 

 stationary. And yet we must have expended 

 more than twenty million foot-pounds of en- 

 ergy in overcoming the attraction of the earth 

 and lifting the weight to its new position. 

 This amount of energy would be sufficient to 

 impart to the weight a velocity more than ten 

 times greater than that of the swiftest cannon 

 ball; or, if converted into heat, would be 

 many times more than sufficient to raise the 

 iron weight to dazzling incandescence and 

 then vaporize it. Now, in lifting the weight, 

 this large amount of energy has disappeared 

 utterly. We can not believe that the whole 

 or any part of it has been annihilated; it 

 must, in some form, be resident somewhere. 

 I think no one will contend that this energy 



is resident, in any form, in the cold, motion- 

 less pound-weight. I believe it was absorbed 

 by, and is now resident in, the ether through 

 which the weight was raised. Conversely, if 

 this be true, a falling body must acquire its 

 energy from the ether through which it falls. 

 This is a fundamental idea to which I invite 

 attention. Faraday glimpsed it long ago, and 

 others have appreciated it more clearly since 

 his time. But, so far as I am aware, no one 

 has realized its significance. 



This view of gravitation implies that the 

 ether is endowed with very great intrinsic 

 energy in some form. Many scientists now 

 hold that the ether is so endowed, and that the 

 amount of this intrinsic energy is enormous. 

 Sir Oliver Lodge ' appears to regard this 

 energy as potential in form, and estimates the 

 intrinsic energy of a single cubic millimeter 

 of the ether to be almost inconceivably vast. 

 He says, " All potential energy exists in the 

 ether." Sir J. J. Thomson says, " All kinetic 

 energy is kinetic energy of the ether." 



I conceive the ethereal energy involved in 

 gravitation to be kinetic rather than potential, 

 the latter involving strain or stress. Newton, 

 and later Maxwell, assumed that bodies pro- 

 duce a stress in the ether about them, of such 

 nature as to account for gravitation; but they 

 were unable to imagine any physical cause for 

 the stress. 



All the past theories of gravitation of which 

 I am aware, except the corpuscular theory of 

 La Sage, appear to regard gravitating matter 

 as the seat of the gravitative influence, the 

 surrounding ether, by induced stress or other- 

 wise, acting simply as the medium of trans- 

 mission. I can not see that any of these the- 

 ories accounts for the energy acquired by a 

 falling body. 



My own view of gravitation differs from 

 these radically. I believe that kinetic energy 

 of the ether is the fundamental cause of gravi- 

 tation; and that a gravitating body plays a 

 secondary role only, in disturbing the nor- 

 mally uniform distribution of the ether's en- 

 ergy, in a manner I shall endeavor to explain 

 later. 



- " The Ether of Space." 



