Lightning Conductors

;The line of danger, whether from the burning or lifting power of lightning, is the line of strong and obstructed currents of air, of the greatest aerial friction.” Trees, church spires, wind-mills and other tall structures, obstruct the aerial currents, and hence their exposure to danger. The highest objects of the landscape, especially those that are nearest the thunder cloud, will receive the lightning stroke. The more elevated the object, the more likely is it to be struck. Of t o or more objects, equally tall and near, the lightning is invariably found to select the best conductor of electricity, and even to make a circuitous path to get to it. Hence the application and evident advantage of metallic rods, called lightning conductors, attached to buildings and ships. A lightning conductor should be pointed at top, and extend some feet above the highest part of the edifice, or mast. It should be made of copper, which is a better conducting medium than iron, and more durable, being less corrosive. It must be unbroken throughout its length, and extend to the bottom of the building, and even some distance into the ground, so as to conduct the electricity into a well or moist soil. If it be connected with the lead and iron work in the structure of the house, it will be all the better, as affording a larger surface, and a readier means of exit for the fluid. In a ship, the lower end of the conductor should be led into communication with the hull, if of iron, and with the copper sheathing, if a wooden vessel; so that, spread over a large surface, it may escape more readily to the water.

138. Precautions against Lightning.—Experience seems to warrant the assumption that any building or ship, fitted with a substantial lightning conductor, Lightning evinces as it were a preference for metallic substances, and will fly from place to place, even out of the direct line of its passage to the earth, to enter such bodies. It is therefore well to avoid, as much as possible, gildings, silvered mirrors, and articles of metal. The best place is perhaps the middle of the room, unless a draught passes, or a metallic lamp or chandelier should be hanging from the ceiling. The neighbourhood of bad conductors, such as glass windows, not being open, and on a thick bed of mattrasses, are safe places. The quality of trees as lightning conductors is considered to depend upon their height and moisture, those which are taller and relatively more humid being struck in preference to their fellows; therefore, it is unwise to seek shelter under tall and wet trees during a thunderstorm. In the absence of any other shelter, it would be better to lie down on the ground.