the Capacity of Gold-leaf Electroscopes. 255 



In applying this urethod, the gold-leaf electroscope was 

 mounted on a stand and a microscope with micrometer scale 

 focussed on the gold-leaf. The calibration curve was first 

 obtained for a range of 60 to 150 volts. The Grerdien con- 

 denser with a capacity of 053 E.S.U. was taken as standard 

 of capacity. The electroscope was charged to 135 volts, and 

 after ten charge and discharge operations the final potential 

 was read off by the electroscope. Two extra short wires 

 were soldered on the charger to facilitate the charge and 

 discharge operations. The following values were obtained : — - 



Charger plus leaf system, 



3-87, 3*92, 3-96, 3*92, 3-94, 3*98, 

 3-96, 3-94, 4-08, 3-98, 3'94, 3*96. 

 Mean = 3'95 E.S.U. 

 Charger only, 



3-17, 3'07, 3*21, 3-30, 3*19, 3'33, 



3-17, 3-21, 3-17, 3-28, 3-19, 3'12. 



Mean = 3'20 E.S.U. 



The capacity of the gold-leaf system, therefore = 0*75 

 + •04 E.S.U. at about 140 volts. 



A second set of observations gave 0*71 ± 0*02 E.S.U. 



A final value may be taken as 0*73 ± '03 E.S.U. 



Owing to the fact that the deflexions of the gold-leaf 

 could be measured to within \ volt, the probable error works 

 out at about half that deduced above from Barratt's own 

 observations, but it is still considerably larger than either 

 of the previous methods. 



The Capacity of an Electroscope at Different Voltages. 



0. T. R. Wilson found the capacity of his Exner's electro- 

 scope to be sensibly the same for 100 and 200 volts, the 

 variation in capacity, due to the change of position of the 

 gold-leaf, being too small to be detected by his method. 

 Barratt found it to be practically independent of the amount 

 of divergence of the leaf. Lester Cooke, whose method is 

 more sensitive, found the capacity to be 0*85 for 200 volts 

 and 0-91 for 300 volts. 



It appears that there should be an increase in capacity tit 

 higher voltages on account of 



(1) Proximity of the gold-leaf to the earthed case due 

 to increased divergence. 

 and (2) Extra work done in lifting the gold-leaf to a greater 

 height at the higher voltage. 



