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-S7A' ll'/LL/AM SJEAfENS, F.K.S. 159 



protected coils were placed at various points within the 

 of cahle as it was coiled in the ship's bold, the insulated 

 leading-wires being tiiken into the testing cabin. These arrange- 

 ments proved of great utility in saving this and subsequent 

 cables from destruction ; for, although the external layers of 

 cable remained cool to tbe depth that mercury thermometers 

 could be inserted, the coils placed in the interior of the large 

 mass indicated a steady rise of temperature which had reached 

 J)8 Fahr. when the official test was made. A few degrees of 

 additional rise of temperature must have destroyed the insula- 

 tion of the cable ; I therefore urged that cold water should be 

 poured over it. This was not effected without strong opposition 

 on the part of the incredulous ; but when at last the water of 

 the Thames, which was covered at the time with floating ice, 

 was pumped over the cable, it issued therefrom at the tempera- 

 ture of 78 Fahr., thus proving the general correctness of the 

 electrical indications previously observed. 



It may be here remarked, that in consequence of this practical 

 test, the Government consented to the construction within the 

 ship's hold of water-tight iron tanks, and also to the cable being- 

 submerged in water during its passage from the works to its 

 destination, precautions which have ever since been adopted in 

 laying submarine cables. 



Stimulated by these results, it occurred to me that an instru- 

 ment of more general application might be constructed for 

 measuring the temperature of inaccessible places ; and that on 

 the same principle, a reliable pyrometer might be made, an in- 

 strument of great requisition in the useful arts for obviating 

 the uncertain and contradictory statements regarding the tem- 

 perature at which smelting and other operations are accom- 

 plished. Various practical difficulties were encountered in working 

 out these problems, which have, however, been gradually lessened 

 or overcome, and my labours have resulted in the production 

 of several types of thermometrical and pyrometrical instru- 

 ments. 



When the temperature of an inaccessible place whose tem- 

 perature has to be measured is not above the boiling point of 

 water, the thermometer coil is variously constructed, according 

 to the position in which it may have to be placed. 



