Professor Melsens thinks it is worthy of note that, although copper is a better conductor of electricity than iron, it has less molecular strength. Where thin iron wire would simply be beaded—without losing its conductivity—by an exceptionally strong charge of electricity, copper wire of the same thickness would by a similar charge be dissipated to a black powder. Professor Melsens has verified this in some very interesting experiments. The large use of iron in his system of conductors on the Hôtel de Ville, Brussels, was rendered imperative by reason of the enormous cost of sufficient copper for such an extensive system. But Professor Melsen’s experiments, nevertheless, give some support to the selection of iron for large and complete works of this kind.
Sir William Snow Harris, in his arrangements for the protection of the Palace of Westminster from lightning, has endeavoured to perfect the general conductivity of the whole mass of the building, and so make it assume the same relation to the electric discharge as if it were a complete mass of metal. Westminster Palace differs in one important respect from the Brussels Hôtel de Ville—the general level of the roofs is covered with iron coated with zinc, and in many places directly connected with the earth by cast-iron water-pipes. The roofing thus constitutes, although imperfectly, and only to a limited extent, a protection of itself. Sir William Snow Harris had, therefore, chiefly to provide for those portions of the building which are above the general level of the roofs, and, by the use of ample conductors of copper, to make up for the comparatively low conductivity of the roofing and the iron pipes which connect it with the earth.
From the terminal which forms the highest point of the large central tower is brought a copper tube of two inches diameter and one-eighth of an inch in thickness, the joints of which are secured by solid screw-plugs and coupling-pieces. This tube is carried down in the south-west angle of the tower and fastened to the masonry by metallic staples. At the junction of the tower with the roofs the tubing is, or at any rate was, thoroughly connected with the metal of the roof, and then continued to the earth in as straight a course as practicable, and there terminates in two projecting branches made of solid copper rod. By carrying this copper tubing direct to the earth, instead of terminating it in the metal-work of the roof, the electrical discharge obtains a conducting medium of the same power throughout, in place of having to leave a high power for one of lower conductivity.
The Victoria and Clock Towers, which are each 300 feet high, are both fitted with a copper band, five inches wide and a quarter of an inch thick. These run down the walls, and are connected with the metal of the roof, and also with the metallic rail of the staircase within each tower. The ornamental turrets and pinnacles of St. Stephen’s Porch are protected by small bands of sheet-copper, two inches wide and one-eighth of an inch thick; these are also placed in connection with the metal of the roof.
The north and south towers of the central block, and the north and south wing towers of the front facing the Thames, have attached to them bands of sheet-copper running from their respective vanes to the roofing below. The bands are connected with the metal of the roof, and are then carried down independently to the earth, in a similar manner to that adopted on the large central tower.
The only other prominent portion of the edifice is the ventilating shaft of the House of Commons, where, during the sitting of Parliament, a coke-fire is generally burning, and from which, therefore, a stream of warm and rarefied air is constantly being emitted. The conductivity of an ascending column of warm vapour is known to be great, and accidents from this cause are of frequent occurrence, although very often they are not ascribed to their true source. To obviate this danger, the ventilating shaft is provided with a copper tube conductor, fixed on its eastern side, and connected with the metal of the roof.
This short description of the measures adopted by Sir William Snow Harris for the protection of Westminster Palace contains all the salient points of the system which at that time, some twenty years ago, was doubtless the best that could be devised. But, although nearly 4,000l. was spent upon this work, from that time to this, as far as can be ascertained, these lightning-conductors have never been tested! It is therefore very possible, and indeed probable, that on the occurrence of any very heavy thunderstorm they would be found wanting, and considerable damage would ensue, the extent of which no one can estimate.
