The Influence of Telegraph Wires on Lightning.

Otago Witness, Issue 1582, 18 March 1882, Page 29

The Influence of Telegraph Wires on Lightning.

Some interesting facts in the above connection have recently been brought out by M. Montigny through observations along a railroad telegraph line in Belgium. It appears that the wire for a considerable distance passes along extensive lines of poplar trees,' while the road rises gradually from a plain to an elevation of about 200 ft. A close examination shows that along this route only about 1 per cent, of the trees have been struc.k by lightning on the plain, and on the slope about 25 per cent., while upon the highest portion of the line not less than 64 per cent, of the trees show evident marks of injury from lightning. M. Montigny distinguishes three kinds of injuries : First, the bark torn and detached on a limited part of the trunk ; second, a furrow, straight or (rarely) spiral, made on the tree, from near the wire, down to the ground ; third, a peculiar oval wound, with longer axis vertical and lips coloured light brown The furrows, which are probably due to the most violent discharges, are relatively most frequent on the upper and western slope, which the storms usually reach first. M. Montigny is of the opinion that the lightning, while provoked by the wire, does not strike that first and then the tree, but strikes the tree directly. His conception of the process is to the following effect: Suppose a thunder cloud charged with positive electricity. A long telegraph wire under it, though insulated, may acquire as great negative tension in the nearest part as if in direct communication with the ground ; and the tension is greater the nearer to the cloud. While the inductive influence affects the wire most, objects that are near, such as trees, share in the influence, according to their conducting power. The lightning is attracted in the direction of the wire, yet does not strike it ; the insulating cups present an obstacle to its prompt and rapid escape to the ground. It finds a better conductor in a neighbouring tree wet with rain.