548 



a sm ff 

 As is easily seen from figure 1, a=z — - — and 



hence da 



dasm (p db ,^^ , . j , -,11 77 



z db = a — , if the attraction changes with the amount ao. 



6' b 



By the change of direction da, the force acting 

 in the horizontal direction H becomes Rda, R 

 being the resultant of a and b. 



If there is a change of mass a with da, then 



da = 



da sin rp da 



b a 



^^S 1- i^et the difference of attraction for two sub- 



stances be 1/1Ü000Ü0, then cZ« = 0,000342" or in radians 1/600000000. 

 In order to give an idea of the sensibility of the apparatus and 

 to calculate the effect to be expected with a given value da, I now 

 give some details of the arrangement, a sketch of which is given 

 in figure 2. 





Fig. 2. 



Experiment with quartz cylinders, mean weight of each 0,888 g. 



Time of oscillation (complete) of torsion rod with quartz cylinders 

 350 sec. 



Time of oscillation (without cylinders) 186 sec. 



Distance of the centres of quartz cylinders 7,6 cm. 



Moment of inertia of quartz cylinders K^ = 2 X 3,8' X 0,888 = 

 = 25,6 g. cm'. 



Moment of inertia rod -j- cylinders K= 25,6 -f 10,1 = 35,6 g.cm'. 



