Moving Charged Spheres. 167 



the maximum value of the magnetic force were used instead of 

 the average. This was largely an accidental result, a sufficient 

 number of reversals not having been made. 



It would have been desirable to have made a larger number 

 of reversals in each series, but after the apparatus had been 

 running for some time the bearings heated so much that it was 

 impracticable. 



The following table gives the values of the ratio of the 

 units obtained from the above readings : 



No N A I 6 V 



1 42 6'7 -00364 26 2'6 10 10 



2 55 10-6 '00355 31 2'6 



3 55 9-0 -00355 31 3*1 



4 49 11-3 -00298 29 2*9 



5 41 5-5 -00280 15 2'7 



6 48 1-0 -00280 15 2*6 



Average. 2-8 10 10 



These results may be taken as fairly representing all that 

 have been obtained. The agreement between theory and experi- 

 ment is fully as good as could be expected when all the uncer- 

 tain elements in the determination are taken into consideration. 



These uncertain elements are: (1) The actual charges carried 

 by the spheres and the effect of surrounding bodies, especially 

 the plate coated with tin-foil covering the lower end of the 

 magnetometer tube. This tin-foil is cut into strips about 1 

 millimeter in width and its effect must be small. (2) The 

 non-uniformity of distribution of electricity upon the spheres 

 so that the charges cannot be regarded accurately as concen- 

 trated at their centers. (3) Errors in reading the deflection of 

 the needle due to outside disturbances. 



Experiments have also been made with the direction of 

 motion of the spheres reversed. The results obtained are 

 similar in every respect to those given above, except that they 

 are reversed. Experiments using only a portion of the 10,000 

 cells of the storage battery gave results which agree fairly well 

 with the preceding. The deflections were too small, however, 

 to expect very close agreement. 



Jefferson Physical Laboratory, Harvard University, Cambridge, Mass. 



