Page:Popular Science Monthly Volume 25.djvu/704

688 without the remotest chance that they would ever be touched by the terrific discharges that were flashed through the walls of their prison-cell in such close propinquity to them. What happened in the case of the birds in this experiment assuredly would happen also in the case of any building that was encaged in metallic rods in a similar way. No demonstration of a mere physical fact could possibly be more absolute or more complete.

The Hôtel de Ville at Brussels is a large mediæval building, inclosing in its center an open quadrangular court, and surmounted in the middle of its principal face by an elaborately pinnacled tower, 297 feet high, with a gilt statue of St. Michael at the top, standing upon a prostrate dragon and flourishing a drawn sword above his head. There are four galleries on the spire beneath the statue, and there are also six spire-crowned subordinate turrets, and three parapeted gables projecting above the roof from other parts of the building. The statue of the saint is reared upon a lead-covered cupola or platform, and Professor Melsens determined that the point of its sword should serve as the culminant point of his system of lightning-rods; but he also took the precaution of very largely re-enforcing this highest terminal by surrounding the base of the lead-covered platform at the feet of the statue with a chevaux-de-frise of outwardly and upwardly branching rods, constituting a radiant circle of tufted points or aigrettes. There were altogether forty-eight of these points projecting round the feet of the statue to a distance of eight feet in all directions. From these radiating aigrettes, and from the statue standing above, a series of eight iron rods were carried down along the face of the tower and the slope of the roof, through an entire length of 310 feet, to the interior court-yard. But as these rods descended along the perpendicular face of the building they were joined by other similar rods from the various subordinate turrets, pinnacles, gables, and ridges, which all had their own systems of terminal points rising up toward the sky. There were altogether 426 points projecting up from the building. An observer looking down from one of the elevated galleries of the spire took in at a glance quite a little forest of spikes bristling up into the air, which were all in direct metallic contact with the main stems of the conductors.

An even more ample provision was made for the connection of this system of conductors with the ground. The vertical rods were first collected into an iron box fixed about a yard above the ground in the inner court, and filled with molten zinc so as to unite the whole into one continuous block of metal. From the hollow of this box twenty-four iron rods, two fifths of an inch in diameter, issued, and of these a third part was carried to an iron cylinder sunk in a well, another third was connected with the iron water-mains of the town, and the remaining third was put into communication in a similar way with the gas-mains. Professor Melsens estimated that the earth contact which