232 APPLIED SCIENCE 



to the reasoning of many persons who, in 1865, wrote to prove 

 that, even if the cable were found again, it could not possibly 

 be brought to the surface by mere hauling. The argument 

 used was, that such an enormous length of cable must be 

 lifted, stretching east and west on either side of the grapnel, 

 that it would break under its own weight long before coming 

 to the surface ; as one gentleman put it, there was not a suffi- 

 cient length of cable to reach to the surface. This argument 

 had a certain amount of truth in it, but those who urged it 

 did not generally take the trouble to make accurate calcula- 

 tions, and some made erroneous calculations. Stretch a piece 

 of fine chain, 100 inches long, across a floor, lay it straight, 

 and fasten down the ends ; try to raise it in the middle, and you 

 will find that, unless it has been pulled very taut indeed, it 

 will rise an inch or two without difficulty. Even when a 

 cable is supposed to be laid taut, it can be raised to a surprising 

 distance; but the 1865 Atlantic Cable was not so laid ; it con- 

 tained 12 per cent, of slack cable; that is to say, 112 miles 

 of cable lay on about 100 miles of ground. Now, lay the 112 

 inches of chain on 100 inches of floor, and fasten the ends as 

 before. The middle of the chain can now easily be raised 21^ 

 inches from the ground. The chain will then hang on each 

 side of the point of suspension in catenary curves ; the weight 

 supported by the string used to lift the chain will simply be 

 the weight of the chain that is off the ground ; the strain on 

 the cable at the point of suspension will be equal to 83^ inches 

 of chain. '.Phis strain is less than the whole weight of the cable 

 lifted, so long as the angle made by the chain at the grapnel is 

 less than 120 degrees, as will always be the case when more 

 than 6 per cent, of slack exists ; it is a minimum, and equal to 

 half the weight lifted when the cable hangs vertically down on 

 each side of the grapnel, or when the elack is infinite. The 

 more the slack the less the strain, for less cable will be lifted 

 before the grapnel reaches a given height, and the angle at the 

 grapnel will also be more favourable. With 12 per cent, slack, 

 nearly 9| miles must be lifted from the ground to reach to a 

 height of two miles. The weight of Atlantic Cable so lifted 

 would be about 6f tons ; the strain on the cable near the 

 grapnel less than 5 tons. As the cable would bear 7f tons, 



