November 7, 1884.] 



SCIENCE 



439 



with the aid of an auxiliary buoy, as in fig. 4. In 

 any event, we see that the difficulties, and of course 

 the cost, of raising, must be considerable. 



Hence to decrease the weight of the cables would 

 be an important step in advance. If the weight is 

 in general very great, it is because the copper core 

 does not take any part in the strain which the entire 

 cable has to resist. "We know, indeed, that copper 

 cannot bear a breaking-strain greater, at most, than 

 28 kilos per square millimetre. Besides, it would be 



square millimetre, and, which is a very precious 

 property, their increase in length at the moment 

 of rupture does not exceed one or one and a half 

 per cent. 



Let us consider the deep-sea section of cable of 

 the French company from JParis to New York, — the 

 so-called ' Pouyer-Quertier ? cable, constructed and 

 laid in 1879 by Siemens Brothers of London. 



The respective weight of each of its component 

 elements is, per nautical mile, copper core, 220 kilos. : 



Fig. 1. 



elongated by such a strain by a very considerable 

 fraction of its initial length; and, if the core were 

 made to take part in any manner whatever in the 

 strain which the entire cable has to support, it 

 would be drawn out beyond its limit of elasticity, 

 and would remain permanently elongated, whilst the 

 substances in which it is enclosed would return to 

 their natural length. It would result, that, being no 

 longer able to find room in a sheath which had be- 

 come too short, the copper wire would take a sinuous 

 form in its gutta-percha envelope, and would occasion 

 at certain points ruptures, the effect of which would 

 be to decentralize the wire, to perforate the layer of 

 insulating matter, and finally to open out a fault in 

 the cable. 



But there exists an alloy (silicium bronze) which 

 can be drawn out into wires having a conductivity 

 equal to that of copper, and a mechanical resistance 

 equal to that of the best iron. The use of this alloy 

 would render it possible to set free the coating of the 



Fig. 3. 



gutta-percha, 180 kilos. ; hemp, or an equivalent, 80 

 kilos. ; 18 wires of galvanized iron of 2 millimetres in 

 diameter, 860 kilos. ; external hemp and composition, 

 400 kilos. : total, 1,740 kilos. Total diameter, 30 mil- 

 limetres. Total mechanical strength, 8,000 kilos., the 

 wires of the covering being supposed to be of iron. 

 Weight under water, 450 kilos. It can support its 

 own weight without breaking for a length of from six 

 to seven miles. 



The Atlantic presents from north to south, and at 

 about an equal distance from each continent, a sort 

 of longitudinal ridge, in which the depths vary from 

 300 to 400 metres. This ridge spreads out, in 50° 

 north latitude, into the region which has received 

 the principal wires connecting England and France 

 with the United States. On both coasts there are 

 depressions in which the bottom is at the depth of 

 from 4,000 to 6,000 metres. The one on the east 

 extends from the south point of Ireland to the lati- 

 tude of the Cape of Good Hope, and its left-hand 



Fig. 2. 



cables from a part of the strain which it now has to 

 resist, and to diminish, consequently, their dimen- 

 sions and weight. Wires are now made of this alloy, 

 having a conductivity of from ninety-seven to ninety- 

 nine per cent of the standard, which at 0° C, and 

 with the diameter of a millimetre, have a resistance 

 of 20.57 ohms per kilometre. These wires do not 

 break with a less strain than from 45 to 48 kilos, per 



Fig. 4. 



boundary follows the general outlines of the west 

 coasts of Europe and Africa. The two_others, the 

 north-western and the south-western, form two 

 basins, bordering respectively on the United States 

 and the Antilles and South America. 



In these depressions soundings have shown certain 

 zones in which the depths exceed 6,000 metres, the 

 principal of which are found to the west of the Cana- 



