308 E B. Rosa — Determination of v, the Ratio of the 



20-2399 20*2372 20'2170 



20-2358 20-2336 20'2348 



20-2350 20-2382 20-2250 



20-2250 20-2315 20*2401 



Meau= 20-2328 + correction for the bar, -0038 = 20-2366 .-. r\ — 



10-1183 cm. 



Ball B. Following are six diameters. 



17*7468 17-7408 17.7429 



17-7465 17-7452 17-7407 



Mean = 17-7438 + correction for the bar, -0034=17-7472 .-. r' B = 

 8-8736. 



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 furnish- 

 ing 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 millimeter, and in B the varia- 

 tion 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 uow have : 



12-6805X10-1180 



C' A = =50-069. 



A 12-6805 — 10-1180 



12-6805X8-8735 



C' B = r— =29-556. 



B 12-6805 — 8-8735 



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

 pending cord passes is 0*35 cm. and its area -g-aVoth part of 

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

 than the area ; therefore the capacity is diminished probably 

 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 ex- 

 ternal surroundings. The two graphite resistances, the two 

 tuning forks, and different resistances from box A were 

 variously combined, and at temperatures ranging from 17° 

 to 25° C. The shell and ball were occasionally re-adjusted, 

 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 elimi- 

 nating to a large degree constant errors, while of course the 

 single observations do not agree as well among themselves as 



