SIR WII.IIA.M SIEMENS, F.K.S. 8 I 



for measuring resistances. Supposing the coil to have been 

 adjusted to represent at zero 100 units of resistance, then for every 

 1* Fahrenheit the resistance would increase by 0*4 of a unit. The 

 advantages of this thermometer were, that whilst it could be placed 

 at almost inaccessible points, it could be read at all times with 

 great accuracy. In coiling the cable on board he inserted several 

 of these thermometers at different layers of the coil. The coil 

 remained nearly a week on board without his being able to test it ; 

 at the end of that time it was at once apparent that there had 

 been a spontaneous generation of heat. On the 10th November, 

 1859, the tests of the cable had given 553 millions of units per 

 nautical mile at the temperature of 49 Fahrenheit. On the 21st 

 of the same month, when the cable was first tested on board, the 

 gutta-percha resistance per nautical mile had diminished to 

 199 millions, showing a considerable increase of heat, unless, 

 indeed, the decrease was due to a fault. On the 1st December it 

 was only 61 millions, showing a further rise of temperature. At 

 the gutta-percha works the standard resistance per nautical mile 

 was 100 millions of units, at the temperature of 75 Fahrenheit. 

 The different resistance thermometers inserted in the cable gave 

 the following temperatures : 84, 75, and 62 ; thus proving that 

 the heat was unequally developing itself throughout the mass, the 

 highest temperature being about 3 feet below the upper surface 

 of the coil. On the 2nd of December the insulation or gutta-percha 

 resistance had decreased to 54 millions of units, and the tem- 

 perature had increased about 3 Fahrenheit in every part. Water 

 was then applied to the cable, and after some hours the temperature 

 was sensibly diminished. The cable had, till then, given no 

 external signs of heat ; the temperature of the hold itself was 

 not greater than 00, nor would a mercury thermometer, placed in 

 any part of the hold, indicate a higher temperature ; yet, when 

 large quantities of water at 42 Fahr. were poured on, it issued 

 from the bottom of the hold at 72, corroborating the results of 

 the electrical observations. This occurrence proved that it had 

 been most injudicious not to have carried out the original plan, of 

 having the cable placed in water-tight tanks on board the ships. It 

 also led to the supposition, that the destruction of several previous 

 cables, more particularly the Atlantic cable, which had been coiled 

 wet on board, might, very probably, have been owing to the same 



VOL. II. O 



