1G8 



Induced by such facts and considerations, the British govern- 

 ment, in the year 1846, selected ten vessels to wear suits of 

 lightning conductors, and sent them to different parts of the world 

 and into all climates during one year, and, finding every ship 

 effectually protected, before the year 1848, furnished every 

 vessel in the British navy with a similar protection, and the 

 East India Company followed the example of the British 

 government. 



The Committee therefore do not hesitate to declare their 

 belief that "the exemption of buildings from injury by light- 

 ning, through the protection of lightning rods, has been such 

 as to Justify the general confidence reposed in them. 



2. Have not single trees and groves afforded greater pro- 

 tection than the metallic rod ? 



It admits of no doubt that trees serve as natural conductors, 

 and especially those, of which the leaves are linear. A case in 

 point is quoted in Franklin's Letters. A Mr. Wilcke saw a 

 large fringed cloud strongly electrified, and extending its 

 inferior surface towards the earth, which suddenly lost its 

 electrical character in passing a forest of tall fir trees. The 

 ragged and dependent portions shrank back upon the main 

 cloud, and rose up as it were from the earth. 



The conducting power of trees results only from the water 

 they contain ; for dry wood, especially when baked, becomes a 

 non-conductor ; water by the estimate of Mr. Cavendish, has 

 to iron a conducting power of only one to 400,000,000. 



Whether a grove would adequately protect a dwelling, 

 depends entirely on the quantity of metal used in the construc- 

 tion of the latter. It appears that the trees which have been 

 visited by thunderbolts have not been able to protect them- 

 selves. In other words the obstruction to the current of 

 electricity has been such as to furnish no passage to a large 

 quantity of the fluid, as in the case of lightning rods badly 

 insulated, which have been forsaken by the fluid for a better 

 conductor. 



Among the trees struck and more or less injured by light- 

 ning the past year, have been noticed sycamores, pines, oaks, 

 apple trees, elms and locusts. If trees possess a higher power 

 of conduction than a moistened bundle of wooden rods of the 

 same height, it is attributable to the increased evaporation 

 from their leaves and branches ; especially is this true, when 

 the electrical condition of the atmosphere is highly intense. 



