Page:Popular Science Monthly Volume 3.djvu/49

Rh with other evidence." Attention is called in the report to the "remarkable fact that in almost all cases small cables had been found liable to mishaps, while the heavier the cable had been the greater had been its durability." The report is full and complete, and establishes principles which up to the present time have uniformly guaranteed success, while the neglect of them has as uniformly resulted in partial loss or failure.

The loss of cables was found to be attributable to the following causes: First, and the most important of all, from imperfect manufacture, resulting without doubt, prior to this date, from inexperience of the materials for insulating the copper wire, and from ignorance of the fact discovered by Prof. Thomson about 1856, viz., that some kinds of copper wire were no better than iron for the purpose of conductivity, and that it required carefully-selected copper to give the desired standard, which may be represented by a copper wire one-tenth of an inch in diameter, being equal to an iron wire one-third of an inch in diameter for electrical purposes. All cables manufactured previous to this date had no advantage from this discovery.

There appear to have been mechanical difficulties in keeping the copper conductor in the centre of the insulating medium, so that the copper was sometimes found to be almost visible under the light film of gutta-percha which covered it. The electric current soon weakened this film, stronger currents were used to overcome the weakness of the signals, and the cable was soon destroyed. Experience about this time had established that a cable from the commencement of its manufacture to the time of its being laid should be tested under water and under pressure, and kept as much as possible under all the conditions in which it was meant to continue.

Attempts to lay cables from sailing-ships towed by steamers was another source of failure. The ships had not enough steerage-way when met with strong head-winds, and too much slack was paid out. It was difficult under such circumstances to steer a straight course, and sailing-ships possessed no power of being readily stopped when a fault or accident occurred.

Many accidents happened from inexperience in the method of paying out cables; at the present day the wonder is, that they should have succeeded so well with the rude methods and inexperience which then existed, and not that there should have been many failures and much recrimination. Reading the history of these first attempts to place a network of cables at the bottom of the ocean fifteen and twenty years ago, is a good deal like reading the old stories of the early voyages of discovery. There are difficulties and disasters peculiar to every attempt, and the grand result is that, one way or another, they were overcome, or else they suggested such modifications that their recurrence was avoided, and an accident to a well-manufactured cable no longer constitutes a loss.