1923] Proceedings of the Academy of Science 19 



underlying Einstein's theory of universal gravitation. It was indi- 

 cated that the differences in results given by the theories of Newton 

 and Einstein are surprisingly small, despite the fact that the theories 

 have few points of resemblance, and proceed from totally different 

 assumptions. The difficulties of finding natural phenomena which 

 will verify Einstein's theory are very great, but finally three were 

 arrived at. These are : the deviation of a ray of light from a recti- 

 linear path, or deflected for example by the attraction of the sun; 

 the advance in the perihelion of Mercury over a period of a century ; 

 and the shift of solar light lines to the red end of the spectrum. 



Dr. Henderson sketched in outline the fundamental principles 

 of Generalized Relativity, and derived the equation of the curve 

 taken by a ray of light. A figure which was exhibited, as well as 

 the calculations, showed that the deviation according to Einstein's 

 theory, amounted to 1.74". This figure, which was exactly twice the 

 amount given by the Newtonian theory, was verified (within thir- 

 teen per cent) by two astronomical expeditions sent out by (jreat 

 Britain during the World War, one to Principe, the other to Sobral. 

 Since the time of Leverrier, it has been known that there was a dis- 

 crepancy of approximately 43'' in a centurj^ between the actual ad- 

 vance of the perihelion of ]\Iercury and the computed value accord- 

 ing to the Newtonian theory, even allowing for all the known in- 

 fluences. From the equation of the orbit, as computed by the Ein- 

 stein theory, and the known values of the constants, it was shown 

 that the advance for the perihelion of Mercury came out to be about 

 43''— a most remarkably accurate determination. Last of all, it was 

 shown by a simple computation that a ray of light from the sun, 

 being of greater wave-length and higher frequency (i. e., redder) 

 than a ray from a terrestrial source, would cause a shift of the 

 spectral lines an appreciable amount toward the red end of the spec- 

 trum. Only quite recently, by isolating the solar ray in a vacuum, 

 the French physicist Perot has shown that the actual shift, for 

 cyanogen, affords entirely satisfactory agreement with the value in 

 Angstrom units computed according to the Einstein theory. 



Effect of an Electric Field Upon Colloids in Non-conducting Liquids. 

 N. B. Foster. 



X-Ray Spectra from Crystals. J. B. Derieux. 



