386 THE PHYSICAL GEOGRAPHY OF THE SEA. 



tlie spirallj-served iron wire, it is only necessary to refer to rig- 

 ging on board ship that is laid up with a heart-piece or centre 

 strand. The strands of the rope, like those of the iron wire, are 

 laid spirally about the hearty and when the rope has been subject- 

 ed to a strain, " Jack," to xise his own language, always finds " the 

 life gone out of the heart." Certainly a spirally -laid rope will 

 stretch more than the straight centre-piece about which it is so 

 laid. Such was the strain brought by the brakes upon the cable 

 on board the Niagara, says an eye-witness, that "large quantities 

 of tar are pressed out of the cable as it enters and leaves the ma- 

 chine, and fall into tubs which are left near the machine for its 

 reception. Of this stuff a couple of ordinary sized barrels full are 

 collected each day and thrown overboard."^" 



Here was force enough to impair insulation by stretching the 

 gutta-percha, or to injure conducting powers by stretching or 

 breaking the threads of the conducting wire ; for, as I said, when 

 the Niagara and Agamemnon were paying out this cable last sum- 

 mer in the deep sea, and when the brakes were holding back with 

 a strain of 2000 or 3000 lbs. on the cable, the heart suffered first. 

 The gutta-percha would outstretch the copper, and then the seven 

 small copper threads composing the conducting wire were attack- 

 ed in detail, and thus the strength of the conducting wire was 

 often tried without any perceptible giving way. It was impossible 

 to have the strain to come upon all the threads of the conductor 

 exactly alike; probably, therefore, first one parted and then an- 

 other, so that in the whole distance each one of the seven may 

 have parted many times; sometimes one alone, and sometimes 

 several, perhaps all, or all but one or two at the same place ; for 

 the parting of any one facilitated the parting of the rest, and all 

 in the same place. One conducting wire would have been better, 

 both in an economical, electrical, mechanical, and Neptunian point 

 of view. 



At first the fractured surfaces, with their crystalline points, were, 

 it may be supposed, bright, and the galvanic current could leap 

 the little chasms with comparative facility ; but use tarnished them, 

 and the leaps became more and more deficient. Hence the pas- 

 sage of intelligible messages at first, and their gradual cessation, 

 and the subsequent failure of the cable to give any signs of life. 



* Mullaly's Telegraph Cable, page 2G4. 



