549 



^^ 4jt» 35,7 

 F'or the torsion couple aS' we find trom *S =^ "-^Tr, — = 0,0115 



cm'' g. sec.~2. 



Hence force per radian twist 0,0115/3,8 = 3,03x10-3 djnes 



= 3,09 X 10-6 g. 

 Distance scale to mirror = 540 mm. 

 A displacement of 1 mm. observed in the telescope corresponds 



1 



to a rotation of -——. 



2x540 



A difference of the positions of the balance equal to 1 mm., 



when pointing first West than East, corresponds for the single effect 



to a force measured by an angle of , and therefore equal to 



-^ ^ 4X^40 



2160 ^ 



The vertical force acting on the cylinder is 0,888 g. 



If the effect is , then we have (see above) Rda = 



1000000 



^ ^:!^ 10-8=: 1,44 X 10-9 g. 



6 



We therefore see that with the sensibility used, 1 mm. of the 

 scale corresponds to an effect of 1 in 1000,000. In many cases the 

 result is certainly smaller than 0,1 mm. 



7. Results. We will now summarize the results obtained. In 

 --the first experiments the position of rest of the rod was deter- 

 mined from three succeeding extremities of vibration. The presence 

 of the observer, however, brings about a marked disturbance by 

 convection currents. Preference was given in the subsequent obser- 

 vations to the noting of the final position of rest, actually attained 

 after about one hour. 



Experiments were made with quartz, calc-spar, lead oxide, uranium 

 oxide, uranyl nitrate. 



Quartz. The 2 cylindrical quartz rods were 25 mm. long and 

 of 4,5 mm. diameter. The axis of the cylinders lay in the vertical 

 plane through the rod of the balance. The crystal lographic axis was 

 perpendicular to the axis of the cylinder. I determined its position 

 before the beginning of the experiments, by means of observations 

 with the polariscope, and noted it by means of a small cross, cut 

 by a diamond, in the surface of the cylinder. 



Experiments in the cellar. The annexed table gives an example 

 of results for cylinders with crossed and with parallel axes. 



