The area of protection covered by the conductor is not so great as is generally supposed. It is limited to a distance about three or four times the length of the conductor above the roof. Thus a conductor standing out five yards will protect an area stretching only about fifteen or twenty yards away. This depends also to some extent upon the nature of the place and the materials of which the house is constructed. Buildings are often struck by lightning because the number of conductors has been insufficient for the extent of the edifice to be protected. To remedy this defect, conductors are made with a number of separate stems--veritable wire traps in which to catch the lightning. This system, the invention of a Belgian physicist, M. Melsens, decreases considerably the risks of destruction, and is much more economical than the erection of a number of separate conductors. A conductor of this kind has been installed on the Hotel de Ville at Brussels, which has been well protected from lightning ever since, whereas previously this building had been struck by lightning several times in spite of the single conductors with which it was supplied. The metallic trellis is in communication with the sewers. The slaughter-houses of La Villette, the Hôtel Evigné, and other buildings in Paris, are provided with similar defences. The Eiffel Tower boasts several such multiplex conductors. It has often been struck by lightning, but no one who has happened to be up it at the time has ever suffered any damage therefrom. The lightning strikes the conductor sometimes from out the actual cloud--curious photographs have been taken of this. The Eiffel Tower is in itself a gigantic lightning-conductor. Portable conductors have been invented from time to time--silk umbrellas without iron ribs, and clothes of indiarubber and such-like; but they have all been childish things. * * * * * Without allowing one's self to get lightning, so to speak, on the brain, it is well to take certain precautions during a storm. The first and principal one is not to get under a tree. The second is to give a wide berth to telegraph posts, so as to avoid contact with the sparks that may issue from them. Movements of the air having the effect of preparing an excellent route for the fluid, it is well not to run in a storm. It is well also not to ring a bell. It is well, also, to avoid being in the neighbourhood of animals, in view of their attraction for lightning. In houses, doors and windows should be closed in order to avoid draughts. It is well to keep away from the chimney, too, as well as from metallic objects. But lightning always has its caprices. It is this that makes its study so interesting. CHAPTER X PICTURES MADE BY LIGHTNING