50 
Proceedings of the Royal Society 
4. On the Disruptive Discharge of Electricity. By Alexander 
Macfarlane, D.Sc., and P. M. Playfair, M.A. 
{Abstract.) 
During the months of November and December of this Session 
we have investigated certain questions suggested by the results 
already communicated to the Society. 
Difference of Potential required to pass a spark betiveen (1) two 
equal spherical balls at different distances , (2) a plate and ball at 
different distances , and (3) a plate and point at different distances. 
A series of observations was taken for each of these, and on three 
successive days, without altering the arrangement of the apparatus 
or the charge of the electrometer. The couple of small Leyden jars 
were attached to the conductors of the Holtz machine, as we had 
previously found that it was impossible to observe the discharge 
between a plate and point with any degree of accuracy when the 
capacity was small. 
Two Balls , each of § inch diameter . — The series of observations 
for the two balls is a more minute and extended investigation of a 
problem we took up and solved approximately before. We have 
observed more minutely the values of the readings at the smaller 
distances, and also noted the cause of the irregularity at the ends. 
We found that at 80 mm. small violet sparks began to pass before 
the principal white spark, and that the reading was then more am- 
biguous than for smaller distances. Escape from the conductor was 
first noticed at 120 mm.* 
Plate and Ball . — We employed a tin plate 8 inches diameter, 
and one of the brass balls used in the previous experiment. The 
curve obtained is not very different from that for the two balls ; it is 
somewhat more circular. Small sparks passing before the large one 
were observed to begin at a shorter distance than in the previous 
case. Another irregularity at the end was due to the passing of two 
large sparks. Finally, the electricity began to escape from the 
insulated wires. 
Plate and Point . — The plate used was the tin plate of the pre- 
* Hence the irregularity previously observed is not due to the escape of 
electricity into the air, but to the passage of small sparks between the 
electrodes. 
