ON THE ELECTRICAL PROPERTIES OF PURE SULPHUR. 
109 
Let 6 be the first elongation of the galvanometer needle. 
Let C be the capacity of the condenser. 
Let V be the potential difference of the coatings in terms of the Clark cell. 
Let K be the ballistic constant of the galvanometer. 
Then when the deflexion is small and the logarithmic decrement can be neglected, or 
eliminated, 
CV = K 0 ; K = CY/0. 
We considered that the best way of obtaining a mean value in terms of the divi¬ 
sions of the microfarad would be to take several sets of observations, calculate K 
from each and then use this mean value to enable us to find the capacity of the 
condenser. The results are as below. 
Table YII. — Yalues of K (Galvanometer constant). 
Fraction of microfarad. 
Voltage. 
Elongation. 
K. 
•2 
if Clark 
205-0 
•0002251 
•2 
198-4 
•0002.326 
Another 1/3 standard 
1/6 Clark 
204-5 
•0002427 
Mean value of K = ’0002335. 
The observations on the sulphur were repeated with 21 Clark cells, as it was 
found that the galvanometer sensitiveness had changed since the day before, when 
the numbers given were obtained. In this way the mean deflexion was found to be 
195'2 divisions. 
Hence 
^ K6 -0002335 x 195-2 
° “ Y “ 21 
"00217 microfarad. 
Subtracting "00004 for key and leads, 
C = 213 X 10~ 20 C.G.S. 
Corrected capacity, therefore, is 213 X 10 -20 . 
If 
A be the “ effective area ” of the film ; 
d ,, thickness of the film ; 
/x ,, specific inductive capacity ; 
Y ,, ratio of the units ; 
Itt.AC.V 2 . 
- y 
P = 
