Ratio of the Electromagnetic to the Electrostatic Unit. 327 



It is perhaps somewhat accidental that these values coincide 

 so closely with the values of the radii found by the first 

 method. Their importance is not insisted upon further than 

 as furnishing satisfactory confirmation of the results of the 

 other and more accurate method. 



It will be seen that in ball A no diameter differs from the 

 mean by as much as a tenth of a millimetre, and in B the 

 variation is still smaller. This deviation from perfect sphericity 

 has no appreciable effect upon the value of the capacity calcu- 

 lated from the ordinary formula. We now have 



12-6805 x 10-1180 

 12-6805 -10-1180 



c A = ,1 nZ, Z.::Z = 50-069. 



_ 12-6805 x 8-8735 _ 

 L B ~ 12-6805 - 8-8735 " 29 556 ' 



The radius of the hole in the shell through which the sus- 

 pending cord (O, fig. 3) passes is *35 cm., and its area -^qq 

 of the area of the shell. The capacity is diminished in a less 

 ratio than the area ; therefore the capacity is diminished pro- 

 bably not more than a hundredth of one per cent. — a quantity 

 wholly negligible. 



Electromagnetic Capacity. 



A series of observations on the electromagnetic capacity 

 by the method described was made, extending from March 28 

 to June 8, under a variety of circumstances as to weather and 

 external surroundings. The two graphite resistances, the two 

 tuning-forks, and different resistances from box A were 

 variously combined, and at temperatures varying from 17° to 

 25° 0. The shell and ball were occasionally readjusted, and 

 between April 16 and May 4 the condenser was taken apart 

 and its electrostatic capacity determined. Further, in order 

 to measure the graphite resistances the apparatus as shown in 

 fig. 1 was each time disconnected and put together again. 

 All these variations must have had the effect of eliminating to 

 a large degree constant errors, while of course the single 

 observations do not agree so well among themselves as they 

 otherwise would. Following is the last observation made, 

 given as a specimen :— 



Eesistances a : W 1930'0-< 2 > 1940=1736-0 



< 3 > 1932-0 -W195'5 = 1736-5 

 ( 5 >1932-0-< 6 > 197-0 = 1735-0 

 (7 > 1932-5-^ 196-5 = 1736-0 



Temperatures : A = 22°-3, B = 23°-0, Graphite = 2 3°-0. 



