4d 



AN OAK TREE STRUCK BY LIGHTNING. 



Bt the Kev. ARTHUR GRAY. 



Two days ago I went to see an oak on Whitfield lawn, which had been 

 strack by Ughtning during a recent thunderstorm. It was a remarkable sight^ 

 The upper part of the tree was shivered into splinters, laxge branches broken off 

 and thrown to the ground; the tree, in fact, had become a perfect wreck 

 Only the lower part of the trunk was standing, and this was completely stripped 

 of the bark. I observed pieces of bark thrown to a considerable distance; 

 and I also remarked longitudinal fissures in the standing portion of the trunk. 



There was no appearance that I could discern of anything hke com- 

 bustion. The whole gave the notion of a violent explosive force actmg from 

 the centre of the oak, forcing open the cracks in the surface wood, and blowing 

 off the bark in fragments, this being but sUghtly attached to the tree, and hence 

 offering feeble resistance. . 



The object of this paper is to offer my ideas as to the proximate cause 

 of these effects. I am not aware whether there is any novelty m them, 

 as similar notions may have occurred to others. It is usual to say that the 

 effects in question are caused by the electric fluid. But this is obviously a 

 vague expression, conveying no very definite idea. Without entering into 

 a^y discussion as to the nature of electricity, what is the immediate cause of 

 these phenomena? I assume, what is generaUy allowed, that the tree acts 

 as a conductor of electricity from the thunder-cloud to the earth. If the 

 tree were a good conductor, like a metallic wire or Ughtning rod, no particular 



effect would be produced: the electricity would pass harmlessly to the ground. 

 But though it is capable of conducting, a tree is not a good conductor. Per- 

 fectly dry wood, entirely free from moisture, would hardly conduct aU : but 



living wood, being full of sap, is able to conduct after an imperfect manner. The 

 current of electricity then does not pass down the tree freely as it would down a 

 metaUic rod, but is retarded; and the denser the nature of the wood, such as 

 an oak, the more it is retarded. Now, electricity is weU known to be con- 

 vertible into heat under such circumstances. I conceive, then, that a portion 

 of the electricity, in its passage down the tree, being converted by the retar- 

 dation into heat of an intense character generates steam, or superheated water- 

 vapour from the moisture of the sap. The powerfully-expansive agency of 

 this is familiar to us alL May it not be considered as sufficient to explam the 

 destructive effects which I have described-the splintering of the thinner portion 

 of the tree-the deep fissures in the more resisting trunk and the forcible 

 projection of the bark. 



The subject is an interesting one, and I should be glad if these remarks 

 should elicit discussion upon it. 



