438 M. Gay-Lussac on Conductors of Lightning. [Dec, 



may abandon it for the wet surface of the wall. A further 

 motive for selecting this side of the building is, that the direction 

 of the lightning may be determined by that of the rain, and 

 moreover, the wet surface, being a conductor, may attract the 

 lightning by preference to the paratonnerre. 



Observations on the Efficacy of Paratonnerres. 



The experience of fifty years demonstrates that when con- 

 structed with the requisite care, paratonnerres effectually secure 

 the buildings on which they are placed from being injured by 

 lightning. In the United States, where thunder storms are 

 much more frequent and formidable than in Europe, their use is 

 become general ; a great number of buildings have been struck, 

 and scarcely two are quoted as not having been saved from the 

 danger. The apprehension of the more frequent fall of light-? 

 ning on buildings armed with paratonnerres is unfounded, for 

 their influence extends to too small a distance to justify the 

 idea that they determine the lightning of an electric cloud to 

 discharge itself on the spot where they are erected. On the 

 contrary, it appears certain from observation, that buildings 

 furnished with paratonnerres are not more frequently struck 

 than formerly. Besides, the property of a paratonnerre to 

 attract the lightning more frequently, must also imply that of 

 transmitting it freely to the ground, and hence no mischief can 

 arise as to the safety of the buildings. 



We have recommended the use of sharp points for the para- 

 tonnerres, as having an advantage over bars rounded at the 

 extremity, by continually pouring off into the air, whilst under 

 the influence of a thunder cloud, a current of electric matter in 

 a contrary state to that of the cloud, which must probably have 

 some effect towards neutralizing the state of the latter. This 

 advantage must by no means be neglected ; for it is sufficient to 

 know the power of points, and the experiments of Charles and 

 Romas with a kite flown under a thunder cloud, to be convinced 

 that if sharp pointed paratonnerres were placed in considerable 

 numbers on la ty places, they would actually diminish the elec- 

 tric matter i the clouds, and the frequency of the fall of light- 

 ning on the surface of the earth. However, if the point of a 

 paratonnerre should be blunted by lightning, or any other cause, 

 we are not to suppose, because it has lost the property we have 

 mentioned, that it has also become ineffectual to protect the 

 building it is intended to defend. Dr. Rittenhouse relates, that 

 having often examined the points of tlfe paratonnerres in Phila- 

 delphia, where they are very frequent, with an excellent tele- 

 scope, he has observed many whose points have been fused ; but 

 that he never found that the houses on which they were erected 

 had been struck by lightning since the fusion of the points. 



