180 Trans. Acad. Sci. of St. Louis. 



When the large masses are in place 



T x = 2tt I — — - (2) 



Mm' v ' 



•i 



D + 2bG 



r 2 



Here D is the directive constant of Eq. (1), b the dis- 

 tance between the centers of the two suspended masses 

 m', and r the distance between the suspended masses and 

 the large masses M . The equivalent of the brass rod is 

 included in m f . 



When the large masses are electrified, if the time of 

 vibration is increased to T 2 and we assume that this is 

 due to a decrease in the value of the gravitation con- 

 stant G, then 



Tt = 2tt / — - - (3) 



From these equations 



_n_ Tt—T? v Jl (A . 



100 _ T 2 —Tx 2 X T 2 2 (4) 



The time of vibration was determined by means of a 

 chronograph belonging to the department of astronomy 

 of the University. The key was snapped when the mean 

 reading passed the cross-hair of the telescope. The 

 mean reading was obtained from the reading of the four 

 extremes of the two complete vibrations which immedi- 

 ately preceded. The values here given are the mean of 

 six complete to and fro vibrations and the probable error 

 does not in any case exceed 0.25 sec. 



Observations March 10, 1916. 



T — 623.0 sec. 

 Tx = 614.5 sec. 

 T 2 — 625.0 sec. 



n 



By Eq. 4, — 1.23 



100 



