84 THE SCIENTIFIC PAPERS OF 



was now cool. It was about to be transferred to other vessels, 

 and he should again carefully watch it. The temperature, at 

 present, had descended to below 60, and the insulation was very 

 perfect. His experience had not been the same as that of a 

 previous speaker, for he had invariably found, that after a cable 

 had once been heated, it never returned to the same perfect state 

 of insulation as before ; implying that some slight change had 

 taken place in the constitution of the gutta-percha, which had 

 not, hitherto, been well ascertained. He would also observe, that 

 less tar than usual had not been used in the Rangoon cable, for 

 the sake of facility in testing ; if it was made drier than other 

 cables, it was for a reason entirely disconnected with the depart- 

 ment of the electrician. 



ON A NEW RESISTANCE THERMOMETER. 

 BY C. W. SIEMENS.* 



To PROFESSOR JOHN TYNDALL, F.R.S., &c., Royal Institution. 



3, 'GREAT GEORGE STREET, WESTMINSTER, S.W. 

 ,, Dec-emln'r. 1860. 



MY DEAR SIR, 



You will probably be interested to hear about a very direct 

 application of physical science to a purpose of considerable prac- 

 tical importance, which I had lately occasion to make. Having 

 charge, for the British Government, of the Rangoon and Singa- 

 pore telegraph cable, in so far as its electrical conditions are con- 

 cerned, I was desirous to know the precise temperature of the coil 

 of cable on board ship at different points throughout its mass, 

 having [been ledj.by previous observations to apprehend spon- 

 taneous generation of heat. As it would have been impossible to 

 introduce mercury thermometers into the interior of the mass, I 

 thought of having recourse to an instrument based upon the 



* Excerpt Philosophical Magazine, Vol. XXI. 1861, pp. 73-74. 



