BRUSH— KINETIC THEORY OF GRAVITATION. 57 



TABLE II. 



Zinc-Iron 15^/^ hrs. "1 



g,/ .< r Mean 17 hrs. 



Iron-Bismuth 13 hrs. 



121/2 " y Mean 13 hrs. 



3/2 " 



V Mean 7.2, hrs. 

 Zinc Iron Bismuth 



Zinc-Bismuth 7 hrs. 20 min. 



7 " 16 " 



17 hrs. 13 hrs. 



Reciprocals : 



7-2> hrs. 



I I I 



17 13 7-36 



Various further pendulum experiments are contemplated ; and 

 an apparatus adapted to compare the velocities of freely falling 

 masses of zinc and bismuth, and perhaps even measure their differ- 

 ence, if any, has been designed. 



In the foregoing pendulum experiments the only force involved 

 for both weight and acceleration was gravity. In the following ex- 

 periments the accelerating force of a flexed spring was substituted 

 for that of gravity. 



Everybody is familiar with the so-called " anniversary " clock, a 

 s'.ow motion, torsion-pendulum clock adapted to run at least a year 

 Vvithout rewinding. One of these clock movements of the best 

 quality was used, and its regular disc pendulum was replaced by the 

 arrangement shown in Fig. 3. 



a is a very narrow ribbon of tempered steel about 11 cm. long, 

 from which depends the brass member b. Rigidly clamped into the 

 lower end of h is the horizontal brass rod c, carrying at its ends two 

 bismuth cylinders Bl. e e are brass sleeves of equal length, just 

 loosely fitting the rod c, to aid in the first rough adjustment of the 

 cylinders. 



The bismuth cylinders, and a similar pair of zinc cylinders, one 

 of which is shown at the upper left, are all accurately cylindrical, 



