SUBMARINE TELEGRAPHY 233 



it was clearly possible to lift it by mere hauling. Moreover, 

 the strain at the bottom would in this case be four tons, tending 

 to pull in more slack from either side, and thus diminish the 

 whole length lifted and consequent strain. By increasing the 

 length of our experimental chain on the floor, and omitting the 

 fastenings at the end, which in the actual cable only exist as 

 friction in the sand, this effect may be clearly seen, and if, 

 instead of tying the chain to the string used to lift it, the 

 experimenter will fish for the chain from a table with four bits 

 of wire, bent into a fish-hook shape, with their shanks bound 

 together, making a mimic grapnel, the illusion will be complete, 

 and the dredger will be surprised to find with what certainty 

 he can hook the cable on a moderately smooth carpet. In 1866 

 the cable was once fairly hauled to the surface by mere brute 

 force. Calculated from the weight (6^ tons) then on the 

 grapnel, 9 miles of cable must have been hanging by the rope. 

 The catenary formed was such as to require 15 per cent, of slack. 

 The strain at the bottom, of about 3^ tons, had therefore pulled 

 in an extra 3 per cent, along the sand on either side. The 

 strain on the cable was about 4^ tons, but with this strain, or 

 little more, it parted shortly after being brought to the surface, 

 and before, owing to rough water, the necessary stoppers could 

 be fixed to it from the ship. This simply affords another in- 

 stance of the very well-known fact that no engineer should 

 ever depend on obtaining, at all points, the full theoretical or 

 experimental strength of a cable or other structure. There 

 must be a margin. The cable was finally secured by the plan 

 recommended almost unanimously by all who had had experience 

 in similar undertakings. Suppose the chain on the floor laid too 

 taut to come up to the level of the table without breaking ; if 

 we with a pair of nippers cut the chain a few feet to our right, 

 a little will slip over the grapnel, the two ends will hang down 

 vertically, and we shall easily land our prize. Just so when the 

 ' Great Eastern ' had hold of the cable. She directed the 

 ' Medway ' to find it, and lift it three miles nearer to America, 

 she then told the ' Medway ' to haul away as fast as she could 

 to break the cable, and the 'Great Eastern' hauled in more 

 slowly, but fast enough to keep hold of the cable with her own 

 grapnel. When the ' Medway ' got the cable within 400 



