SCIENCE AND PRACTICE. 



was arrived at by us from tests of the Malta- Alexandria 

 cable during the process of sheathing. The difficulty of 

 ascertaining accurately the length of the cable and tem- 

 perature of its interior at any moment, however, precluded 

 the possibility of any mathematical expression with con- 

 fidence. The first, and so far as we believe, the only good 

 results hitherto obtained, are those published by Sir Charles 

 Bright in a paper read recently before the Institution of 

 Civil Engineers. 



Experiments were made by Messrs. Bright and Clark 

 upon four coils of the insulated core destined for the Persian 

 Grulf cable. Each coil had a length of one nautical mile. 

 They were placed in a felted iron tank holding about 1,200 

 gallons. At starting, the coils were maintained for three 

 days in water kept in motion, containing a large quantity of 

 melting ice, and may therefore, at the end of that time, 

 when their resistances were measured, be presumed to have 

 taken throughout the temperature of the water. After the 

 first measurements were made, the water was allowed to 

 increase in temperature very gradually up to 38 C., the 

 gutta-percha resistance being measured at regular intervals. 

 These experiments occupied thirty-three days, during which 

 time nineteen series of observations were made, the mean 

 results of which, reducing the observed resistances at C. 

 uniformly to 100, are as follows : 



