78 | Royal Society. 
rent: thus the resistance of a foot-cube would be very different to 
that of an inch-cube. 
The values of G for the covering of the Red Sea cable, after con- 
tinued ‘electrification for periods of one, two, three, four, and five 
minutes, were calculated in Fhomson’s Absolute British Units, from 
four sets of tests made specially for this purpose on four different 
cables, each about 500 knots long. Tables containing the results of 
these calculations accompany the paper. 
A Table is also given of the resistance of the Red Sea covering 
after one minute's electrification, and after five minutes’ electrification, 
at each degree of temperature, from 5U° to 75° Fahrenheit. This 
Table was formed by means of the temperature curves described in 
the first part of the paper: this Table is here annexed (No. 1). 
Similar Tables were given for the covering of the two experimental 
coils mentioned in the first part of the paper. The coil composed 
of pure gutta percha, gave very regular and complete results. An 
abbreviation of the Table is annexed. 
It was remarked that in the tests of the cable in the iron tanks, 
the resistance after five minutes’ electrification was invariably 
greater with zinc than with copper to cable, whilst the reverse was 
the case with the single knot covered by water. The length of the 
cable, and the condition of immersion or non-immersion, have pro- 
bably some influence on the phenomenon of extra-resistance. This 
phenomenon appears to the author to be of much importance, and 
to demand further investigation. 
The values of G were also calculated from the daily tests of the 
cables during manufacture at many temperatures. These values 
agreed with those given in the Tables above described. The general 
results of the experiments may be summed up as follows. 
The relative loss at various temperatures through pure gutta 
percha has been pretty accurately determined for all ordinary tem- 
peratures, Toa less extent the same knowledge has been gained 
concerning two other coatings containing Chatterton’s compound. 
The latter appears superior at high, and inferior at low temperatures. 
Attention has been drawn to the considerably increased resistance 
which follows the continued electrification of gutta percha and its 
compounds. Some of the laws of this extra resistance have been 
determined, and some suggestions made as to the cause of the 
phenomenon. 
The bounds have been pointed out within which formule may 
be used, which consider gutta percha as a conductor of the same 
nature as metals. 
The resistance of gutta percha has been obtained in units, such as 
are employed to measure the resistance of metals; and by the use of 
Professor Thomson’s formula, the specific resistance of a unit of the 
material has been fixed with some accuracy. 
The resistance of other non-conductors, such as glass and the 
resins, may probably, by comparison with gutta percha, be obtained 
in the same units. 
Incidentally, the increase of resistance in copper with increased 
temperature has been given from new experiments; and it has been 
