463 
Calibration of Leaf.—The instrument can be calibrated by connecting 
to known potentials and noting the deflections of the leaf. A storage battery 
of three or four hundred volts is convenient. Readings should be taken for 
every few volts from 0 to the maximum and a curve plotted. X = deflection, 
Y = volts. Ifa large voltage battery is not at hand a 110 volt D. C. circuit 
can be used making connection to a resistance as in Fig. 5. The voltmeter, 
V, should be read at the same time that the deflection of the leaf is read. A 
calibration curve from 0 to 110 volts can then be obtained. For the higher 
points proceed as follows: Charge the leaf to maximum voltage by means 
of a rubber rod. A body of small capacity, small compared to the capacity 
of the electroscope, 1 or 2 cm., say, is mounted on an insulated handle. A 
coin on a small rubber rod will answer. This is first grounded and then 
touched to the charged system. The gold leaf falls. The capacity is re- 
moved, grounded, and the position of the leaf noted. The operation is 
repeated until the leaf falls to 0 on the scale. 
If Cis the capacity of the electroscope, and 
c is the capacity of the coin, 
Q, the quantity of electricity, 
WreVonslst. 2nd. a 2... potential of the leaf, 
Oli Gln its} liste, PAMol 4 5 & 6 & deflections of leaf, 
then, Q: = CV; = (C+ c)V;2 
. Q, = CV. = (C+ e)V: 
@, = CV, = CL OVarn 
Ce Vi Ve Wes 
C V2 V3 Vice 1) 
The last three or four deflections should be on the part of the scale 
already calibrated. That is, the potentials should be less than 110 volts. 
If V, and V, 4, are known by comparing with d, and d, 4 1 on the calibration 
curve. Since, 
Vn ap Vn 
then, 
V,—1 can be calculated. V,—, being known, then V,,» can be determined. 
In like manner all Vs can be determined up to Vi. Knowing V and the cor- 
responding deflection, d, the curve can be extended up to the maximum 
deflection. 
