October 3, 1913] 



SCIENCE 



473 



Poincare and Fave, Lord Rayleigli,'" and 

 Brace," each hoped to find effects of the earth's 

 translation through the ether in the double 

 refraction of light by crystals, but were unable 

 to obtain such effects. The phenomena of in- 

 terference upon which Young and Fresnel 

 based their wave theory of light have not as 

 yet been completely accounted for upon the 

 principle of relativity. Spectroscopists seem 

 to prefer the use of " frequency " to " wave- 

 length " in their descriptions of monochro- 

 matic radiation.'^ When any action forcibly 

 ejects from an atom a light particle or an 

 electron spinning in its atomic orbit with the 

 speed of light, it is not diificult to perceive 

 that the ejected light-particle would have a 

 circular motion superimposed upon its appar- 

 ent translation throiigh interstellar space. 

 Thus the path of a light particle would be 

 spiral or screw-shaped, wave-length would cor- 

 respond to the pitch of the screw, and fre- 

 quency to the number of revolutions which 

 the light particle makes per second. Possibly 

 a theory of interference may be worked out 

 along this line. 



The new mechanics teaches that the velocity 

 of light, 186,337 miles per second, is our limit 

 of speed ; no body in motion can exceed it, and 

 can only with extreme difficulty approach it. 



The old mechanics taught that a constant 

 force continually acting upon a body in in- 

 terstellar space, would make it go faster and 

 faster without limit. The principle of rela- 

 tivity says that a constant force acting upon 

 a body during successive intervals of time 

 meets a greater and greater opposition to its 

 increasing speed ; and when it has attained the 

 speed of light the power of this force to pro- 

 duce acceleration is exhausted. There is noth- 

 ing, of course, in empty interstellar space to 

 prevent a body from continuing forever with 

 the speed once acquired, except collision with 

 another heavenly body, when perchance, the 

 energy of motion changes the cold colliding 

 matter into a radiant sun. 



"Eayleigh, Phil. Mag., 4: 683, 1902. 



"Brace, Phil. Mag., 7: 328, 1904. 



'^Eunge, Zeitschrift f. Electro cliemie, 18: 485, 

 1912. 



The old mechanics was quite sufficient until 

 the discovery of cathode rays and radium gave 

 us matter in motion outspeeding a thousand 

 times our fastest planet, Mercury. The par- 

 ticles in the stream of cathode rays travel 

 with a velocity of 5,000 miles a second, while 

 those from radium are hurled into space with 

 a speed of 50,000 to 178,000" miles per second, 

 and have become in many instances the mod- 

 em surgeon's scalpel. The physicist, in his 

 search for law with respect to matter, finds it 

 necessary to readapt his mechanics to modern 

 facts. 



The question naturally arises: why should 

 the speed of light be set as a limit to the in- 

 crease of velocity? The answer is that with 

 unlimited speed the possibility arises of a 

 reversal in the order of time. This possibility 

 has been worked out in a curious way by Flam- 

 marion." He makes Lumen, an interstellar 

 traveler, an observer of the battle of Waterloo, 

 and then proceeds to show what would happen 

 if, at the close of the battle, he were moving 

 away from the scene with a velocity greater 

 than the speed of light; he would overtake the 

 light which left the battlefield at the beginning 

 of the engagement, and would see the whole 

 fray in a reversed order of time, like a moving 

 picture film run ofl^ backward. 



Secondly, if Lumen were at rest and the 

 earth were speeding away from him with a 

 velocity greater thau that of light, he would 

 see the battle in its natural order, but all 

 would proceed with stately slowness. 



Thirdly, if Lumen were at rest and the 

 earth were speeding toward him with a velocity 

 greater than the speed of light, he would again 

 see the battle in the reverse order, as the last 

 fire from the guns would come to Lumen from 

 a point nearer to him than the light from the 

 first volley. 



With any experiment thus repeated three 

 times. Lumen would be able to determine 

 whether he were at rest and the earth in mo- 

 tion, or vice versa; in other words, he would 



"^ Rutherford, Physikalische Zeitschrift, 13: 

 1178, 1912. 



" C. Flammarion, ' ' Stories of Infinity — Lumen, ' ' 

 p. 74, 1873. 



