TRANSACTIONS OF SECTION A. 405 
splashes, that the surrounding gas practically determines them. In the 
case of ‘ positive’ splashes the surrounding gas has very small influence. 
If the pressure of the surrounding air is reduced, the appearance completely 
changes. At a pressure of about 17 cms. in air the negative splash has 
a very definite appearance, showing two new dark spaces with triangular 
‘squirts’ of discharge extending between them. 
The radical difference between positive and negative discharges is very 
pronounced. If a triangular or rectangular electrode is placed on the 
plate, the branched figures obtained tend to leave at the corners of the 
plate when this electrode is made positive, but to leave at the sides (and 
at right angles thereto) when it is the negative terminal. 
The effects of a magnetic field and of a blast of air over the plate were 
also exhibited. 
5. The Photographic Action of Alpha Rays. By T. Kiyosurra. 
6. On Secondary Radiation by Gamma Rays on Different Metals. 
By Professor A. S. Eve. 
7. On the Active Deposits from Actinium in Uniform Electric Fields. 
By W. T. Kennepy, M.A. 
In es paper an account was given of some measurements on the 
amount of active deposit from actinium obtained at different pressures on 
two parallel plate electrodes provided with guard rings and placed about 
2mm. apart. 
The deposits were obtained on both electrodes under a field of 250 volts. 
As the pressure was decreased from atmospheric the amount of active 
deposit on both electrodes gradually increased, passed through a maximum 
value, and finally at low pressures rapidly decreased. The maximum 
activity was obtained at different pressures for the two electrodes, in each 
of the gases hydrogen and carbon dioxide and in air, and the maximum 
cathodic deposit was found to be about 2°7 times that obtained on the anode 
in each of the gases. 
The total deposit on the two plates obtained in air at varying pressures 
was found to be approximately the same, whether an electric field was 
applied or not. The total active deposit was also found to be increased 
on both electrodes when potentials higher than the sparking ones were 
applied. The relative coefficients of diffusion for the emanation from 
actinium were found to be—Carbon dioxide, 1; air, 13; and hydrogen, 42. 
8. The Effect of Light on Sulphur Insulation. By F. W. Bares. 
During a series of experiments on the ionisation of the air in closed 
vessels, the author used an electroscope in which the leaf system was 
supported on sulphur insulators. When an attempt was made to calibrate 
the instrument, large variations in the rate of leak were noticed, which 
seemed to depend on the intensity of the light falling on the leaf system. 
A series of experiments was then undertaken to discover whether any such 
definite relation existed. 
It was found that the average day-rate of leak was greater than the 
average night-rate, that bright sunlight falling on the insulator increased 
the rate very greatly, while even partially excluding the light decreased 
it perceptibly. By intercepting some of the sun’s rays by means of either 
cobalt blue or red glass the rate of leak was much lessened, and by totally 
