Page:Popular Science Monthly Volume 25.djvu/699

Rh recognized as dangerous to animals taking shelter near their trunks, because they do not convey a lightning-discharge with sufficient rapidity to the ground, and because they are worse conductors themselves than animal bodies. But the discharge will not in any case leave a good conductor, well connected with the ground, to strike a living animal placed near its course. The terminal rod of a conductor was ordered to be two and a half inches square at its base, and to taper to a height of twenty or thirty feet above the building, with a needle of platinum, or of copper and silver alloy, at its top. The base of the rod was to be plunged into the ground, and then led away from the building for fifteen feet, being finally turned down into a hole or well fifteen feet deep, and then divided into root-like ramifications, the whole being well packed round with charcoal to protect the metal from rust. In a dry soil the earth contact was to be twice the length of the one which was deemed sufficient in a wet one. It was above all things insisted upon that too great precautions could not be taken to give the lightning a ready passage into the ground, as it was chiefly upon the freedom of this passage that the efficacy of the conductor must depend. A conductor with insufficient earth contact was stigmatized as being not only inefficacious, but dangerous, because it would attract the lightning without being able to convey it to the ground.

It was further asserted in this most comprehensive and notable report that an experience of fifty years had proved buildings to be effectually protected when good conductors were placed on them. In the United States a number of conductors had been known to have been struck, but in not more than two of these cases had the buildings themselves suffered any damage. It was generally assumed, from the data then at command, that buildings which were protected by lightning-rods were not more likely to have the discharge brought down in their neighborhood on account of the presence of the rods, and it was also held that, even if they were open to such a liability, this could be of no practicable moment, because the power of a conductor to attract the lightning more frequently would, of necessity, also involve the capacity to convey it more freely to the ground. Points were spoken of as undoubtedly tending to neutralize the tension of a charged cloud. Dr. Rittenhouse was referred to as having observed in Philadelphia that the points of lightning-conductors were frequently blunted by fusion without the houses to which they were attached having been in any way injured.

The views advocated in this early code of instructions have been dwelt upon it some detail, in order that it may be seen how effectively this document laid down the broad principles of defense which are acted upon even at the present day. This instruction, after it had been stamped with the approval of the Academy of Sciences, became a sort of popular manual under the weight of this sanction. The Government gave force to the instruction by providing that it should