DEC 1 1922 



DISCUSSION OF A KINETIC THEORY OF GRAVITATION, 



II; AND SOME NEW EXPERIMENTS IN 



GRAVITATION. 



Second Paper. 



By CHARLES F. BRUSH. 



A year ago I had the honor to present to this Society the first 

 paper under the present title. The second, or experimental part of 

 that paper, appeared to show that equal masses of zinc and bismuth, 

 also of iron, and presumably of other metals and substances, do not 

 have exactly equal weights ; in other words, that the mass-weight 

 relationship differs in different substances. For instance, a given 

 mass of bismuth appears to weigh a little more than an equal mass 

 of zinc ; or, to state it differently, as in the pendulum experiments 

 following, gravity acts more strongly per unit of mass on bismuth 

 than on zinc. 



When established, this is a fundamental fact of supreme impor- 

 tance ; and the present paper is devoted wholly toward its confirma- 

 tion, leaving theoretical consideration for future papers. 



As the following experiments relate only to the mass-iveight dif- 

 ference between zinc and bismuth, I shall, for simplicity, refer to it 

 as the " zinc-bismuth effect." 



Of the several experiments detailed in the first paper, that of the 

 two gravity pendulums is the simplest and most easily understood, 

 the most accurate and reliable, and has brought out most suggestions 

 of possible sources of error. The latter are all considered in the 

 following review and extension of the pendulum experiments; and 

 the conditions as to length of rods, and weight and shape of bobs, 

 have been widely varied. In every case the former zinc-bismuth 

 effect has been confirmed, and in no instance has there been any 

 negative or equivocal result. 



PROC. AMEK. IHll. sec, VOL. L\I, M, : OV. l6, I922. 



167 



