660 



PROTECTION AGAINST LIGHTNING. 



water is suddenly converted into vapour. The expansion thus 

 caused strips off the bark at the points of least resistance, 

 and if the hark be smooth and thin, large pieces of it may be 

 removed (Fig. 291). The wood may also be split from the top 

 of the tree downwards, the lightning entering at the fine twigs 

 on the top of the tree and running down the stem straight or 

 spirally according to the direction of the fibres. 



2. Damage done, 

 a. General Account. 



The effects of lightning on a tree are very various ; if the 

 tree be split, the bark is usually removed only in a narrow 



Fig. 292. Horizontal lightning-stroke along a I c on a beech tree. 

 a Four meters above the ground. I d A short dark line. 



strip on either side of the tree, otherwise, occasionally in large 

 flakes. Even in the former case the tree generally dies, it 

 may be after a few years. 



In other cases, pieces of wood are split off the stem, of all 

 sizes up to several yards in length (Fig. 293). The lightning 

 has even been known- to enter a beech tree 100 years old, in 

 Hesse, on the llth July, 1886, horizontally and then strike 

 down through its axis, as shown in Fig. 292. Sometimes large 

 arms of a tree, or its whole crown, have been broken off by 

 lightning. As a rule, the lightning runs down the tree into 



