86 THE SCIENTIFIC PAPERS OF 



the interior of the mass of the cable, although the coils nearer the 

 top and bottom surfaces did not show yet any remarkable excess 

 over the temperature of the ship's hold, which was at 60 Fahr. 

 The increase of heat in the interior progressed steadily at the rate 

 of about 3 Fahr. per day, and having reached 86 Fahr., the 

 cable would have been inevitably destroyed in the course of a few 

 days, if the generation of heat had been allowed to continue 

 unchecked. 



Considering the comparatively low temperature of the surface of 

 the cable, much incredulity was expressed by lookers-on respecting 

 the trustworthiness of these results ; but all doubts speedily 

 vanished when large quantities of cold water of 42 temperature 

 were pumped upon the cable, and found to issue 72 Fahr. at the 

 bottom. 



Resistance thermometers of this description might, I think, be 

 used with advantage in a variety of scientific observations, for 

 instance, to determine the temperature of the ground at various 

 depths throughout the year, or of the sea at various depths, 

 &c. &c. In the construction of this instrument, care has to 

 be taken that no sensible amount of heat is generated by the 

 galvanic currents in any of the resistances employed. 



By substituting an open coil of platinum wire for the insulated 

 copper coil, this instrument would be found useful also as a 

 pyrometer. 



But, finding this letter already exceeds its intended limits, I 

 shall not enlarge upon these applications, which, no doubt, are 

 quite obvious to you. 



I am, dear Sir, 



Yours very truly, 



C. WM. SIEMENS. 



