[ 57 ] 
IV. Researches on the Electric Properties of Pure Substances. —No. I. The Electrical 
Properties of Pure Sulphur. 
By Richard Threlfall, M.A., Professor of Physics in the University of Sydney, 
and Joseph Henry Drapier Brearley, Deris-Thomson Scholar in the 
University of Sydney. 
Communicated by Professor J. J. Thomson, E. R.S. 
Received April 19,—Read May 24, 1S94. 
[Plates 1-5.] 
Preliminary Statement by Professor Pi. Threlfall. 
In 1886 I began to make .some experiments on the specific resistance of certain 
Australian gums, with a view to finding new insulating material. In connection 
with this I constructed and tested various galvanometers. In 1887 I was joined by 
Mr. J. A. Pollock, and in 1889 we published conjointly in the 4 Philosophical 
Magazine ’ a paper on the “ Specific Resistance of Imperfectly Purified Sulphur,” and 
on the “Clark Cell, as a source of Small Constant Currents.” I also published in 
the same volume a paper “ On the Measurements of High Specific Resistances.” All 
these papers may be considered as preliminary to the present investigation of the 
behaviour of pure sulphur under electric stress, which has gone on steadily since 
June, 1889. The remainder of that year, the whole of 1890, and most of 1891, were 
occupied in preliminary experiments on galvanometers and in making and testing 
various arrangements of electrodes between which the sulphur to be examined was 
placed. This work was carried out entirely by Mr. Pollock. Early in 1891 I was 
joined in the work by Mr. J. Id. D. Brearley, who has worked continuously at the 
subject with me up to the present time. I began the study of sulphur originally 
with the object of discovering the exact electrical properties of a pure, lion-metallic 
substance, and chose sulphur because it appeared to offer advantages in melting at a 
moderate temperature, in being capable of existing in several allotropic forms, and, 
above all, in being capable of being brought to a high degree of purity with compara¬ 
tively little trouble. With respect to the galvanometer, which has enabled us to 
perform the experiments described, so far as its general features are concerned, it 
was designed by me, in 1890, on the lines laid down in the ‘ Philosophical Magazine,’ 
series 5, vol. 28, p. 473; but the detailed design, as well as the actual construction, I owe 
MDCCCXCVI.— A. f 2.4.96. 
