MAKING AND LAYING SUBMARINE CABLES. 161 
ship to the bottom. And the paying-out machinery must be 
so constructed that the requisite force can be exactly applied. 
It is plain that if the retarding force exactly balances the 
external weight of the cable, the latter will be laid quite 
straight; it is, however, found better to run out an excess of ten 
Fia. 102. 
to twelve per cent, of the cable, rather than subject it to such 
a strain. There is also an advantage in this should it after¬ 
wards be found necessary to pick up the cable for repairs. The 
effect of driving the ship at a rate as nearly as possible that at 
which the cable passes out is also very remarkable in reducing 
the strain. 
We see then that the modulus of rupture of a cable should 
greatly exceed the maximum strain to which it will be sub¬ 
jected. It may, daring the laying of the cable be necessary to 
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