t36 Wbolard— Generalised Relativity and Gravitation. 



(19) 



* — L 



ds c 



and that at infinity from the sun 



dt __ l-n .'I .' 

 (h c 



(20) 



which means of course, that the measure of time varies 

 with the strength of the field; that is, events which 

 occupy so much time at one place, will, if observed from 

 another place, actually seem to occupy a different amount 

 of time, the phenomena itself appearing the same, but its 

 rate apparently changing. The atomic and electronic 

 vibrations which produce light-waves will therefore 

 vibrate slower in the sun as observed from the earth 

 than they will on the earth as observed from the earth ; 

 the wave-lengths of the Fraunhofer lines of any element 

 will be longer in the solar spectrum than those of the 

 same lines from a terrestrial spectrum of the same ele- 

 ment; the solar lines should all be displaced systemat- 

 ically towards the red. Some observers have claimed to 

 have found such an effect, although the cause of it could 

 not be safely placed 17 ; but Dr. Chas. E. St. John, using 

 the powerful instruments of the Mt. Wilson Solar Obser- 

 vatory, reaches the conclusion, after a careful investi- 

 gation of the nitrogen (cyanogen) bands in the ultra- 

 violet, that "within the limits of error there is no 

 evidence in these observations of a displacement to 

 longer wave-lengths, either at the center or at the limb 

 of the sun, of the order of 0-008 A, as required by the 

 principle of relativity. " 1S 



16. When we apply our equations to the problem of 

 finding the motions of the planets in the sun's field, we 

 get equations which show that the orbits are ellipses with 

 moving perihelia. The fact is well known that the peri- 

 helion of Mercury refuses to obey the Newtonian theory, 

 moving 40" per century too fast. Many causes have been 

 assigned, but none have been entirely satisfactory, and 

 in 1895 Newcomb adopted as the most probable of all, 

 the hypothesis that the Newtonian law is not quite 



17 Freundlich, Phys. Zeitsehr., 15, p. 369, 1914. Evershed and Royds, 

 Bull. 39, Kodaikanal Observatory. 



18 St. John, Astrophysical Journal, 46, pp. 249-265, 1917; Proc. Nat. 

 Acad. Sci., 3, pp. 450-452, 1917. 



