60 BRUSH— KINETIC THEORY OF GRAVITATION. 



the paper cylinder ends. The performance of the bismuth cyhnders 

 thus equipped was carefully compared with that of the zinc cylinders 

 wearing the same paper caps pushed down to contact. Of course, 

 the paper caps, because of their weight, slightly increased the periods 

 of both zinc and bismuth cylinders. But, within the limits of ex- 

 perimental error, it increased them equally, thus showing no effect 

 from the equalization of air resistances. Hence the paper caps, 

 apparently serving no useful purpose, were not used in the following 

 experiments. 



TABLE III. 



Bismuth Zinc 



Period r 8".9232 Period f 8".9299 



j .9231 8".93i8 ->. .9329 



8" .9228 1 .9226 t .9326 

 .9223 



^■'■'^'-' I '"tf9 



8".9232 8".9302 



^".9247 I 



8".9255 8".9295 



.924 



Mean 



8 .9298 1333 



Table III. embodies the results of a series of experiments with 

 the zinc and bismuth cylinders on the torsion pendulum. Each 

 period is computed from a run of 22 to 24 hours. All the observed 

 periods are given — not those selected from a larger number. 



All bracketed periods were obtained with one setting of the cyl- 

 inders. After one period or set of periods was observed with either 

 pair of cylinders, these were removed from the pendulum frame and 

 the other ]:)air substituted. This involved each time a new and very 

 careful adjustment of the radii of gyration as before explained. 



