THE EFFECTS OF LIGHTNING. 



73 



When trees have been barked by lightning, it frequently happens that the 

 bark is stripped from the base of the trunk upward to a certain height, and the 

 upper part of the tree is untouched. This occurred with several trees in the 

 Champs Elysees at Paris, in a storm which took place in June, 1778. 



The leaves of trees which have been struck by lightning often exhibit the 

 effects of heat on their lower surfaces, but not at all on the superior surfaces. 



All these effects M. Arago thinks are capable of being explained by the 

 vapor of water issuing upward after being evolved by the lightning acting on 

 water contained in the ground. 



They are also capable of explanation by the escape of negative electricity 

 from the ground upward. 



VI. MAGNETIC EFFECTS. 



This class of effects is so well known, and so perfectly explained by the 

 principles established in electro-magnetism, that it will not be necessary to 

 devote any space here to the enumeration of instances of them. 



VII. EFFECTS OF CONDUCTING BODIES ON LIGHTNING. 



Although the properties of metallic substances, and other conductors, in ref- 

 erence to lightning, are capable of being inferred by analogy from the princi- 

 ples of common electricity, yet the difference of the intensity of the atmo- 

 spheric electricity in storms, and the artificial electricity of the machines, is so 

 enormous that it cannot be without great utility to record the circumstantial 

 statements of those effects of lightning which illustrate the influence of conduc- 

 tors when affected by electricity of a tension so much greater than any which 

 can be obtained in ordinary experiments. 



The unvarying preference which electricity gives to conductors over non- 

 conductors in the selection of its route, is strikingly illustrated in the following 

 narrative, addressed to the abbe Nollet, soon after the discovery of the virtue 

 of conductors by the count Latour Landry. 



On the 29th of June, 1763, in a violent thunder-storm, lightning struck the 

 steeple of the church of Antrasme, near Laval. It entered the church and 

 fused or blackened the gilding of the frames and borders of particular niches. 

 It blackened and scorched (demi-grillee) the cruets (burettes), which lay in a 

 small cupboard, and, finally, it pierced two deep regular holes like those of an 

 auger in a marble closet where the church plate was kept, and which was 

 placed in a niche formed in a wall of sandstone. 



These damages were repaired ; the gilding was restored, the holes stopped, 

 and the painting renewed. On the 20th of June, 1764, lightning again struck 

 the steeple. It entered the church at the same place ; blackened the gilding 

 which it had blackened before ; fused that which it fused before ; extended its 

 damage to precisely the same limits, without exceeding them ; blackened and 

 scorched (grillee) the cruets ; and, finally, reopened the two holes in the mar- 

 ble closet. 



The protection afforded by conductors to surrounding non-conductors, and 

 the damage done by lightning in forcing its way to the former, and escaping 

 from them through the latter, is proved by the following instances : — 



When lightning struck the tower of Newbury, in 1754, on the occasion for- 

 merly mentioned, it first destroyed the superior part, which consisted of a pyr- 

 amid of carpentry about seventy feet high. Having scattered this mass of 

 woodwork it encountered a metallic wire which descended through the tower 

 to a point about twenty feet lower. It fused this wire in several places, but 



