Page:Popular Science Monthly Volume 25.djvu/838

ground. But the conductor provided by the electrical engineer acts in precisely the same way, and with equal efficiency, in either case. It provides the means by which the electrical disturbance may set itself at rest in a quiet and unexplosive way. The chief danger that has to be feared is the purely economical one that there is always a tendency on the part of the imperfectly informed public to limit too narrowly the cost, and in that way to impair the efficacy, of the engineer's work. The duty of the engineer is, summarily, to see that his building is adequately covered above by the lines of the conducting network, that the main channel of his conductor is ample for any storm overflow that it can, by any possibility, be called upon to accommodate, and that the outlet to the earth is capacious and free. Even in the present state of electrical science it can, with the utmost confidence, be affirmed, not only that wherever destructive accidents have occurred in association with lightning-conductors, such accidents have, in every case, been due to the circumstance that the conductors have been of faulty construction, but also that in by far the greater number of instances the fault has been in the least conspicuous and least obvious part of the apparatus, where the earth contact has to be established. In his report on the lightning-conductors of the Paris International Exhibition, Professor Rousseau states that it is in this particular that lightning-rods most generally and most flagrantly fail. In one passage of the report he says:

I do not know whether I have defined with sufficient precision what is implied in a good communication with the earth, but I think the principle, at any rate, may be laid down that the communication of a lightning-conductor with the earth can not be considered good if it is inferior to that of any masses of metal that lie in its close neighborhood. If this is the case, it may be anticipated, as has so frequently been found, that the lightning will quit the paratonnerre to pass to the object which is in better communication with the earth. It is thus that buildings have been frequently set fire to by lightning which has leaped from paratonnerres to gas-pipes. In one notable case, after striking the conductor of a church in New Haven, United States, the lightning left the conductor to pierce a brick wall fifty centimetres (nearly twenty inches) thick, to get at a gas-pipe which rose twenty feet out of the ground a little distance off.

We ourselves some little time ago investigated the nature of an accident occasioned by lightning, which so strikingly confirms the views expressed by Professor Rousseau that it is worthy of being specifically brought under notice here. In the year 1865 the tower of the church of All Saints, in Nottingham, was struck by lightning during a severe thunder-storm. The tower was one hundred and fifty feet high, and had a small rope of copper wire, intended to serve as a lightning-conductor, descending along its west face from one of its corner pinnacles to the ground, where the rope terminated by being coiled round a stone buried, a few inches in the dry soil. On the inner face of the same wall of the tower, near its base, and only separated from the con-