The system employed by Mr. R. S. Newall, F.R.S., for the construction and erection of lightning conductors is probably the most complete--and certainly the most representative--of the various methods in vogue in England. The special study Mr. Newall has made of the subject in all its bearings, both theoretical and practical, added to the fact of his possessing at his extensive cable works at Gateshead such exceptional facilities for the production of copper ropes and bands composed of the purest metal, render him one of the first authorities on all matters connected with the application of lightning conductors to buildings. In describing, therefore, the English method, reference will chiefly be made to this gentleman’s apparatus and inventions.
The function of a lightning conductor is twofold. In the first instance, it operates as a medium by which explosions of lightning, or, to speak more accurately, disruptive discharges of electricity, are led to the earth freely, and without the risk of their acting with mechanical force, as they invariably do when compelled to pass on their way to the earth through so-called non-conductors, that is to say, bodies possessed of low conductivity, such as the atmosphere, wood, stone, &c. In the second instance, the conductor acts as a means whereby the accumulation of electricity existing in the atmosphere is quietly drawn off and carried noiselessly into the earth, and dissipated in the subterraneous sheet of water beneath it. Now this accumulation of electricity, always greatly intensified during a thunderstorm, invariably seeks the easiest road to earth; this road is technically called ‘the line of least resistance.’ This line of least resistance is influenced by various circumstances; the resistance of any line may be lessened by the presence of streams of warm vapour or rarefied air such as would come from chimneys, from barns or stacks containing new hay; by a column of smoke, or by the presence of tall trees moist from rain. It is not always easy to find the reason why the lightning takes any particular path, but one thing is certain, that is, it acts under certain fixed principles, and does not take any particular route by chance, but always because it is the line of least resistance. What the lightning conductor really does is to prevent the possibility of an electric discharge within a certain district, for instance, in the interior of a house or other building.