556 Proceedings of the Royal Society 
it further on, he found difficulty in determining “ the relative 
degrees of charge which the small ball acquires before discharge 
occurs, that is, whether it acquires a higher condition in the 
negative, or in the positive state, immediately preceding that dis- 
charge.” The method of our experiments, it appears to me, has 
Solved this difficulty. 
I employed a Thomson’s divided ring reflecting electrometer, 
which has either half-ring insulated. In this instrument Professor 
Swan has substituted a glass dish with a tubulure for holding 
the sulphuric acid in place of the original leaden pan, in which 
the charge of acid was carried On pieces of pumice stone. The 
tubulure allows the acid to be filled in Or taken out with con- 
venience. A piece of platinum foil suspended in the acid, from the 
aluminium needle; completely checks the oscillations, and renders 
the instrument “dead beat.” The terminals for connecting the 
divided rings, which originally projected downwards, now project 
upwards* and, to secure perfect fcontact, are in the form of a helical 
brass Spring passing through a varnished glass tube. The instru- 
ment was set so that the needle when charged was symmetri- 
cally situated with respect to the two halLrings, and the scale 
was set so that the wire-image was in the middle. The Holtz 
machine by which the electricity was produced, was at a distance of 
20 feet from the electrometer. 
In the first series of observations the point used was the conical 
point of a rod of a Henley’s discharger. It was connected by 
means of an insulated wire with one conductor of the Holtz 
machine. The plate used is of 7 inches diameter, and was 
attached to the other stem of the discharger in such a manner 
that the rod was always normal to it at its centre. Both the 
plate and the other conductor of the Holtz machine were in con- 
ducting connection with the earth. Either kind of electricity was 
obtained by charging the one or the other paper conductor of the 
machine by means of a small Leyden jar. As either half ring 
of the electrometer could be insulated and the other connected 
with the earth, readings were taken in both directions. This 
is the meaning of the entries in the record connections direct and 
and a disc is much more continuous with the point negative than with the 
point positive (Phil. Trans, vol. clxix. p. 90). 
