104 REPORT—1890. 
The condensers are placed in the testing room at the Cavendish 
Laboratory and covered by a wood and canvas case to protect them from 
dust. It is not intended that they should be movable. 
After this description of the condensers we will proceed to an account 
of the tests to which they have been 
Fie, 2. subject. The first test was for 
leakage. 
One set of cylinders was put to 
the earth while the other was con- 
nected with a gold-leaf electroscope. 
Anattempt was then made to charge 
them with an electrophorus or a 
small electrical machine, but this 
failed entirely. The electricity 
either sparked across at places 
where the tubes were very close 
together, or, before the potential 
rose sufficiently to affect the electro- 
scope, small fibres or dust particles 
which adhered to the tubes formed 
leaks across ; it was clear that the 
condenser could not be charged to 
the potential of the machine. Tests 
were then applied for leakage when 
the potential was lower. One set 
of tubes was connected to one pole 
of a battery — about thirty-six 
storage cells were gencrally em- 
ployed, having an E.M.F. of 75 
volts—the other set being in con- 
nection with an insulated key ; the 
second pole of the battery was con- 
nected through a galvanometer to 
the key and the condenser charged. 
After an interval, usually about 
five minutes, contact was again 
made at the key; the deflection of 
the galvanometer needle—assuming 
the E.M.F. of the battery not to 
have changed—was a measure of 
the quantity of electricity which 
had leaked from the condensers in 
the five minutes. 
The amount of leakage was 
very different in the two condensers 
and depended greatly on the dry- 
ness of the air and ebonite pillars. 
Thus on March 11, when strong 
acid had been enclosed for some 
time, for condenser I. the leak per 
1 minute amounted to about ‘1 per cent. of the whole charge, while 
with condenser II. it was about ten times as creat. 
The sulphuric acid was removed during the Easter vacation and re- 
Y . 
W.WARWICK SG 
