410 



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 

 constant. At 60 the resistance increases about 20 per cent, in five 

 minutes from this cause. With a positive current, similar results 



