-1859J, WRITINGS OF JOSEPH HENRY. 339 



certainty, be drawn from the phenomena. It simply indi- 

 cates an intense repulsive energy exerted between the atoms 

 of matter in the line of discharge. It sometimes happens 

 when an old tree which has perhaps been moistened by the 

 rain — is struck by lightning, instead of being rent laterally 

 it is broken off transversely, the upper part being projected 

 vertically upward. This effect however is not usually pro- 

 duced, since the force exerted by the tree to resist trans- 

 verse breaking is much greater than that to prevent lateral 

 tearing apart. 



In the passage of electricit}'- from a charged conductor, or 

 from a cloud to the earth, it always follows the line of least 

 resistance and by an antecedent induction determines the 

 course it is to pursue. This is strikingly exhibited by an 

 experiment devised by Sir W. S. Harris. A number of sepa- 

 rate pieces of gold leaf are attached to a sheet of paper. If 

 a discharge sufficiently strong to dissipate the gold and 

 blacken the paper be passed through them, its course will 

 be shown by the blackened parts ; and it is especially worthy 

 of remark, that not only are the pieces out of the line of 

 least resistance untouched, but even portions of other pieces 

 are left unchanged from the same cause. Now these sepa- 

 rate pieces of gold leaf may be taken to represent detached 

 conductors fortuitously placed in the construction of a 

 building. 



The apparently fitful course of a discharge in its passage 

 through a building frequently excites surprise, leaping (as 

 the electricity does) from one conductor to another, and 

 sometimes descending to the earth in several streams ; but 

 that the discharge should leap from one conductor to another 

 through a considerable intervening space of air is not sur- 

 prising, since its original intensity was sufficient to enable 

 it to break through a stratum of the atmosphere of perhaps 

 a mile in thickness before it reached the house. 



Whenever electricity passes through an interrupted con- 

 ductor so as to exhibit the appearance of light, a great in- 

 crease of intensity is always manifested at the point of dis- 

 ruption, as if the charge halted here for a moment until a 



