104 
PROFESSOR R. THRELFALL AND MR. J. H. D. BREARLEY 
nearly to melting, when it began to conduct at 110° C., and the conductivity 
then diminished to about 116° C., when it increased rapidly as the sulphur melted. 
Some films separated from the plates on heating. 
The result of all this was to show us the necessity for a good many small precautions, 
and induce us to concentrate our efforts on the new galvanometer. This work, which 
has already been described, occupied us until September, 1892, when the new 
instrument was got into good working order and the investigation of the sulphur 
proceeded with. Preliminary experiments, therefore, took nearly two years, though 
the work was not continuous, and we blundered a good deal. With increased 
galvanometer sensitiveness came increased difficulty from want of insulation, thermo¬ 
electric effects, &c. These took some time and trouble to overcome, and, as our ex¬ 
perience and the sensitiveness of the galvanometer increased, we were continually 
obliged to repeat our observations. The film was the subject of experiment until 
October 28, 1892, at which time, the plates having come apart, the thickness of the 
film was measured by a large spherometer. The threads having been measured before 
they were put between the plates, and previous work having shown that the plates 
rested exactly on the threads, it was imagined that the thickness of the film would 
be the same as the diameter of the threads. This, however, turned out to be 
an erroneous assumption, for the spherometer showed that the thickness varied 
slightly from point to point, and was more than 1 per cent, greater than the 
diameter of the threads. In the progress of the work it was necessary to reduce 
most of the results with this wrong value (i.e., the supposed thickness of the 
film), but they have been recalculated for this paper. The exact statement of the 
preparation of the film follows. 
Preparation and Properties of Film of September 14, 1892. 
The plates having been scrupulously cleaned, as well as the pure gold dish, some 
twice distilled sulphur (Chance) was melted at a temperature of 145° in the large oil 
bath. This oil bath was really a large oil oven, heated by two long perforated Bunsen 
gas tubes. It took about four hours to heat to 1 20°, and was a proportionally long 
time in cooling; it was not the same oil bath that was used for heating the sulphur 
when undergoing examination. Eight threads, each broken off to a diameter of 
•24 millim., were placed on the lower plate. These threads were about 1 to 2 
centims. long, and their diameter was gauged by a Brown and Sharp vernier 
callipers. The upper plate was adjusted to the sulphur, care being taken to avoid 
the presence of air bubbles by lowering the plate from one end like a microscope 
cover-slip, and at the same time tlie plate was lowered gently enough not to wash 
out the threads. The sulphur stood in the gold dish nearly level with the top of the 
upper plate. After the plates were adjusted as perfectly as possible (examination 
afterwards showed that the adjustment was practically perfect),, the whole arrange- 
