Woolard — Generalized Relativity and Gravitation. 137 



exact. 19 The fact which has, more than anything else, 

 drawn attention to the general relativity theory is that 

 the motion of Mercury's perihelion predicted by it 

 agrees almost exactly with the actual motion. 



17. The truth of. the postulate of general relativity 

 probably cannot be questioned 20 ; as to whether the 

 invariant equations derived by Einstein are the ones or 

 not, future observations alone can tell. The agreement 

 in the case of Mercury "may conceivably be due to acci- 

 dent and, in any case, its evidence is too slender to be 

 regarded as establishing the theory. But we must face 

 the distinct possibility of its ultimate success." 21 



Boulder, Colorado. 



January 24, 1918. 



10 Newcomb, Astronomical Constants, 1895. In connection with relativity 

 suggestions, see Nature, 99, pp. 412-3, 1917, and 100, pp. 33, 1917. 



20 Bumstead (Science, N. S. 47, pp. 59-60, 1918) says, however: "There 

 can be little doubt of its correctness when applied to motions of translation ; 

 speaking in terms of the ether, we may be reasonably confident that it is 

 impossible to detect the effects of uniform translation relative to the ether. 

 But little has been accomplished in extending the theory to motions of 

 rotation; indeed, rotation has always been a stumbling-block to a purely 

 relative theory of motion, as soon as dynamical considerations are intro- 

 duced." See his remarks following this, and also "On the Belativity of 

 Rotation in Einstein's theory," Sci. Amer. Sup., Aug. 18, 1917. In 

 addition see Walker, Proc. Boy. Soc, A, 93, p. 448, 1917. 



21 Bumstead, cited above. As to both the relativity theories, see Einstein, 

 Scientia, May, 1914; and T^gesfragen aus den Gebieten der Naturwissen- 

 sehaften und der Tecnik, Heft 38, Tiber die spezielle unci die allgemeine 

 Relativitatstheorie ■ ' (Gemeinverstandlich), 70 pp. 



