During the months of May and June of this session we have endeavoured to investigate certain questions suggested by our experience of the discharge of electricity through the gases and through oil of turpentine, for which purpose Dr Macfarlane had received a grant from the Royal Society of London.

When paraffin oil (the kind employed for illuminating purposes) was put into a glass vessel, in which were two brass plates arranged in the form of a condenser, and when the plates were charged by means of the Holtz machine, it exhibited the same phenomena as oil of turpentine. Gas bubbles were produced; they did not appear until after the passage of the spark. Once produced, they facilitated the passage of the spark through bringing the electrified surfaces virtually nearer to one another. Hence, when taking observations of the difference of potential required to pass a spark through layers of different thickness of the oil, it was always necessary to remove the bubbles generated by the passage of one spark before electrifying again. This was effected by bringing the discs into contact.