172 



BRUSH— A KINETIC THEORY OF GRAVITATION. 



being on the pendulum formerly occupied by the bismuth weight; 

 then the weights were exchanged as before, the pendulums started 

 together, and allowed to run until the bismuth had gained two beats 

 as formerly. This procedure was for the purpose of verifying the 

 first finding and to expose any considerable difference there might be 

 in the performance of the driving clocks. No such difference was 

 found; yet for verification the same procedure was followed in the 

 next experiments. 



A cylinder of very pure iron was next prepared, of exactly the 

 same height, and approximately the same weight as the zinc and 

 bismuth cylinders, and adjusted for center of gravity with the same 

 care. 



The iron weight or cylinder was then compared with the zinc 

 weight and with the bismuth weight, with the same care used in com- 

 paring the zinc and bismuth as above described. The iron gave 

 results intermediate between those of zinc and bismuth. 



Table I. shows the performance of the zinc-iron, the iron-bismuth, 

 and the zinc-bismuth combinations. The measurements of time re- 

 quired to gain one beat check and confirm each other remarkably well. 



As the pendulums make about 2,388 oscillations per hour, the 

 bismuth gains one beat, or oscillation, in about 17432; but as before 

 pointed out, the real zinc-bismuth effect is only half of this, say, one 



17 + 13 = 7.36 



