1864. | Farrparrn on Submarine Telegraph Cables. 631 
anomalous results. The insulation increased, instead of diminishing, 
as the liquid dissolved out. ; 
The first experiments have for their object the determination of the 
increase of weight of various insulating materials, when subjected to 
enormous pressure under water. A series of insulators were selected, 
such as gutta-percha, india-rubber, Wray’s compound, Chatterton’s 
compound, vulcanized india-rubber, india-rubber compounded with 
carbon, and marine glue. Of these, suitable-sized pieces were pre- 
pared and placed in a strong steel cylinder, and subjected to pressure 
by means of a lever and plunger. Before their introduction into the 
cylinder, and whilst dry, they were carefully weighed in a delicate 
balance. Then, after being subjected to pressure for a shorter or 
longer period, as the case might be, they were again dried on the 
surface, and immediately weighed. The increase of weight due to the 
pressure under water is the measure of the quantity of water which 
had been absorbed, or rather forced, into the pores of the 
insulator. 
Fig. 1 represents the apparatus employed in these 
experiments. © is the large cylinder of steel in which 
the specimens were placed; p, its plunger, 2 inches 
diameter. Fig. 2 shows the general arrangement of 
the apparatus; Lu, the large lever; r, its fulcrum; 
and p, the plunger of the cylinder o, in which the 
weighed specimens were placed. The plunger is guided 
vertically by the box BB, forming part of the general 
case or stand in which the lever is placed. By means 
of weights suspended on the extremity of the lever, the 
requisite pressure could be applied to the water in the 
cylinder c. 
FIC.2 
The temperature in all these experiments was low, sometimes 
several degrees below the freezing-point. In the first experiment with 
Wray’s compound, the cylinder when opened was found to be filled 
with loose ice. 
In the following table the last column shows the gutta-percha to 
be least absorbent, and the india-rubber most so. Wray’s compound 
absorbed more than carbonized india-rubber, but less than pure india- 
