pores. 
X. Proceedings of Learned Societies. 
ROYAL SOCIETY. 
(Continued from vol. xx. p. 550.] 
March 22, 1860.—Sir Benjamin C. Brodie, Bart., Pres., in the Chair. 
‘PHE following communications were read :— 
“On the Insulating Properties of Gutta Percha.” By Flee- 
ming Jenkin, Esq. 
The experiments described in this paper were undertaken with the 
view of determining the resistance opposed by the gutta-percha 
coating of submarine cables at various temperatures to the passage 
of an electric current. 
The experiments were made at the works of R. 8. Newall and Co., 
Birkenhead. ‘The relative resistance of the gutta percha at various 
temperatures was determined by measuring the loss on short lengths 
immersed in water. These experiments are described in the first 
part of the paper. The absolute resistance of gutta percha has been 
calculated from the loss on long submarine cables. These experi- 
ments and calculations are described in the second part of the 
paper. 
Part I. 
The loss of electricity was measured upon three different coils, 
each one knot in length. One was covered with pure gutta percha; 
the two remaining coils were covered with gutta percha and Chat- 
terton’s compound. The coils were kept at various temperatures 
by being covered with water in a felted tub ; and the water was main- 
tained at a constant temperature for twelve or fourteen hours before 
each experiment. 
The loss or current flowing from the metal conductor to earth 
through the gutta-percha coating was measured on a very delicate 
sine-galvanometer. The loss from the connexions when the cable 
was disconnected, was measured in a similar manner. The electro- 
motive force of the battery employed was on each occasion measured 
in the manner described by Pouillet. Corrections due to varying 
electromotive force and loss on connexions were made on the result 
of each experiment. 
A remarkable and regular decrease in the loss was observed for 
some minutes after the first application of the battery to the cable; 
a phenomenon, which the author thinks may be due to the polariza- 
tion of the molecules of gutta percha, or of the moisture contained 
in the pores of the gutta percha. The loss was therefore measured 
from minute to minute for five minutes, with each pole of the 
battery. 
Nineteen tables containing the results, with the reductions and 
curves representing the results, accompany the paper. The following 
results were obtained from the first coil; this was prepared with 
Chatterton’s patent compound. With a negative current between 
the limits of 50° and 80° Fahrenheit, the decrease of resistance is 
sensibly constant for equal increments of temperature; and the 
increase of resistance due to continued electrification is also nearly 
