PROTECTION AGAINST LIGHTNING. 683 



recognized as dangerous to animals taking shelter near their trunks, 

 because they do not convey a lightning-discharge with sufficient ra- 

 pidity to the ground, and because they are worse conductors them- 

 selves 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 light- 

 ning 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 build- 

 ings 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 con- 

 ductor 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 ten- 

 sion 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 



