1 8 THE ADDRESSES, LECTURES, ETC., OF 



being fixed at 100 units, and the law of increase of resistance by 

 rise of temperature of these metals being also known, the tempera- 

 ture of each coil could be easily determined at any time in 

 measuring its electrical resistance. These resistance thermometers 

 might be applied with advantage in many cases where it is de- 

 sirable to ascertain the temperature of inaccessible places, as for 

 instance, in warehouses and on board ship, where hemp, coals, and 

 other self -inflammable goods are stored. 



One of the most important preparatory operations in the laying 

 of cables is that of ascertaining the nature of the ground upon 

 which the cable is to rest, for, however perfect the cable may be, 

 if it is laid upon unknown ground it may very soon come to grief. 

 With regard to shallow seas, there is no difficulty in ascertaining 

 the nature of the ground on which the cable is to rest, whereas in 

 a depth of 2,000 fathoms I have known a single sounding occupy 

 five or six hours. Another drawback as regards deep sea sound- 

 ings consists in the difficulty of identifying the place again, no 

 landmarks being visible. It must always, therefore, be to a certain 

 extent a matter of uncertainty what is the depth below the ship in 

 the open sea. In going across the Atlantic the depths do not vary 

 materially, as there appears to exist a great plateau on which the 

 cable may be laid ; but in deep seas formed by volcanic action, 

 such as the Mediterranean, the depths are very uncertain. It is 

 not impossible, however, that an instrument may be brought to 

 perfection by which the depth below the ship's keel may be indi- 

 cated in the cabin. Such an instrument would be of material 

 service in 'warning the telegraphic engineer of changes in the 

 depth of water in paying out deep-sea cables. The few trials 

 which have been made have amply proved the principle of the 

 instrument, and given promise of ultimate success. 



The patient care and unremitting attention which the prepara- 

 tion of a deep : sea cable necessitates, in order to avoid the chance 

 of a single flaw or error in the arrangements, contrasts singularly 

 with the exciting operation of submerging the same. A well pro- 

 portioned cable of ample strength, and a good paying-out appa- 

 ratus, do much to assure the acting engineer that the cable will 

 sink without being unduly strained either during its descent or 

 after it has reached the bottom ; but an entanglement in the cable 

 tank, the breakage of "a single wire in the spiral sheathing of the 



