May< r — Eatpi run, nts with P> ndiUumrdsotrometi r. 



the Bpheree: and when the Bphereon the rod lias been brought 

 to 2cm. reading od its scale, the deflection on the upper scale 

 pins 2 cm. gives the distance of centers of spheres apart, and 



the force (/') in dynes in the rate <^ 3*4 mm. to the dvue; and 



/ — ]yi < an, l Bince go* — if] ,j = J) sf fikfi tlie sphere, being of 

 i cm. radius, has unit capacity. 



Tnfl >f tin surface of the room and of surrounding objects 



on th< capacity of t/u sphere, 



ij [If we assume [to he within bounds) that the above influences 

 are equivalent to a sphere of 100 cms. radius, concentric with 



rr' 100 



the suspended sphere, we have C = -: — = — = 1*01. This 

 1 r r —r 99 



gives f«>i' the effect of the induction of the room in increasing 

 the capacity of the sphere, the same as would be produced by 

 increasing the radius of the sphere by T \ mm. ; a quantity too 

 small to be taken into account in experiments with this appa- 

 ratus as it is not possible to form the sphere to this degree of 

 precision. We would here remark that this apparatus is not 

 an instrument of extreme precision, though it will measure to 

 -^ of a dyne, and with a sphere of pith, which has -J- of the 

 grravity of cork, it may measure to the -g- 1 ^ of a dyne, 

 if the apparatus is guarded from air currents; but this instru- 

 ment gives the means of readily making electrostatic measure- 

 ments before a class, and of presenting clear conceptions of the 

 nature of these measurements. 



Experiments to determine if apparatus gives the laio,f= ^. 



Eight experiments are given in the following table. The 

 first column gives the number of experiment; the second, the 

 deflections in centimeters of the pendulum ; the third, the 



Exp. 1 



d =■ 

 tfs=115 



D = 5-25 

 D'=lll5 



d 

 -=4o6 





= 4-51 



Approx 



■ir 



" 2 



rf'=2'4 



D= 5-0 

 D'= 7 2 



" 208 



II 



2-07 



ii 



?is 





d=±8 



<r=2 3 



D= 4 8 

 D'= 7-0 



11 208 



» 



212 



it 



A 



- 4 



d =.-!•:. 



<r=2 1 



D= 5*8 



D';= 71 



11 166 



(1 



1*66 





00 





i=s2-66 



</'=0-87 



D= 5-65 

 D'= 9-87 



" 3-046 



(i 



3-051 



ii 



sfor 



" 6 



d='2 7 5 



d'=v:> 



D= 477 

 D'= 6-5 



1-83 



II 



1-85 



it 



* 



•• T 



,/=3 02 

 d'=2Sl 



D= 4-86 

 D'= 502 



" 1-052 



II 



1-0G6 



ii 



* 



" 8 



i=3'10 



cr=2-94 



D = 1 94 



D'= 510 



11 1-054 



«' 



1-066 



ii 



A 



