114 
PROFESSOR R. THRELFALL AND MR. J. H. D. BREARLEY 
C = 208 X 10 20 (uncorrected). 
/1 = 3"697 (corrected for standard). 
A comparison between our condenser and one supplied by Messrs. Clark, Muirhead, 
and Co., may now be given; it was made on Jan. 24th, 1893, at a temperature of 
23'8 C., by means first of the old, and afterwards of the new galvanometer, with 40 
Clark cells by De Sauty’s method. The leakage through the two condensers was 
measured, and found to be so small as only to affect the result in the fifth place; it 
was therefore neglected. We used two 100000 ohm boxes, and a dial box of 10000 
ohms, all by Elliott Bros., but the divisions were not compared with our standards. 
Dr. Muirhead’s value for the '2 microfarad was T996 microfarad at 15° C. 
As we do not know whether the mica plates are shellacked or only paraffined, we 
cannot apply any temperature correction—in any case the two condensers probably 
have about the same temperature coefficients. The result of the comparison was that 
with 100000 ohms out in one branch, the balance lay between 98815 and 98800 in 
the other. Taking 98808 as the mean, the capacity of our *2 division for instantaneous 
charge is ‘20180 microfarad, or say 1 per cent, too large. For the future this value 
will be employed. 
The difference between this value and that formerly obtained is to be ascribed 
chiefly to the difference between the standard selected and the mean of the three 
divisions taken before as a standard. 
It was thought desirable to check this result by another method, both for the 
purpose of obtaining independent evidence, and because the ballistic method takes so 
long to carry out that it is unsuited for measuring the capacity at any given tempera¬ 
ture. The well-known method of De Salty was selected after consideration, the 
sensitiveness of our galvanometers giving us great advantages in carrying it out. By 
observing the initial kick we also hoped to get the instantaneous capacity comparison 
(see Glazebrook, 4 B.A. Report,’ Leeds, 1890, p. 102). 
Bv using 40 Clark cells, a balance for instantaneous charge was given by 100000 
and 1005 ohms out in the two branches, one from a dial box, the other from an 
ordinary box, both b} r Elliott, but not compared with our standards. 
The final corrected result is 
C = -00211, 
IX = 3‘708. 
The sensitiveness of the galvanometer having been increased, as well as our 
experience in using it, it was thought worth while to determine the resistance again 
for the purpose of obtaining a higher limit. 
Date , October I sf, 1892—Voltage, 304 volts. 
Sensitiveness of galvanometer, 3"6 X 10 
meter. 
-12 
ampere per “ half tooth of the micro- 
