Page:Popular Science Monthly Volume 3.djvu/50

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40
THE POPULAR SCIENCE MONTHLY.

The first Atlantic cable failed principally on account of imperfect manufacture, in a great measure arising from undue haste and urgency, but largely owing to insufficient experience. The cable was not tested under water, for fear of rusting the small steel wires of the external covering, and small wires have never since been used; large wires, the larger the better, is now a principle. The copper was not all good. It had often been coiled and uncoiled, and had been exposed to the strong heat of the sun, and to many changes of temperature. Any of these conditions would nowadays be regarded as enough to condemn the most carefully-manufactured cable.

The Red Sea and Indian cables are said to have been imperfectly manufactured and laid too taut, but they were not tested under water from the time of manufacture until they were placed at the bottom of the sea, and this one grand omission, largely due to inexperience, is enough, without the recriminatory points, to condemn to loss and failure any cable whatever.

The cables laid from Cagliari to Malta and Malta to Corfu are said to have failed from imperfect manufacture. One experienced gentleman in his evidence said these cables were "such as nobody should have laid in deep water." It is sufficient at present to know that they have failed from neglect or inexperience, and that they, among other failures, have established the principles which have since insured success.

The want of constant supervision by engineers, exclusively in the interests of the purchasers of the cable, has been a great cause of defective cables. There may often be minute defects in the core itself, or a slightly defective splice which may reduce the electrical condition of a comparatively short length; this may easily be raised above the average standard required by the contract, by the next length being more carefully manufactured. These minute defects must, however, kill the cable in more or less time, and the principle is established that every inch should be tested in course of manufacture, and rejected if there is any irregularity of condition to cause suspicion. There should be constant supervision, and a record of all the tests kept for the purchasers of the cable from the commencement of the contract to its final completion, and continued ever afterward by the purchasers.

The principal sources of injury to cables are—first, moving water, either currents or tides, chafing the cables upon rocks or shingle. Experience has given many costly lessons of the effect of moving water.

Ten years ago it was generally believed that water had very little motion below 50 fathoms, and 100 fathoms was considered a point of great safety. We now know that there are exceptional localities where there is motion in the water at a depth of 500 fathoms. The Falmouth cable was chafed and destroyed at this depth from this cause. The Channel Islands cable was also destroyed from the same cause. The first cable ever manufactured with due regard to the principle of careful supervision, testing under water, and being retained quietly in