372 WRITINGS OF JOSEPH HENRY. [1855- 



The inductive action at a distance which we have described 

 affords a rational exposition of the effects which are per- 

 ceived by persons of nervous sensibility on the approach of a 

 thunder-storm, and may also be connected with the change 

 "which is said to take place suddenly in liquids in an un- 

 stable condition, such as the souring of milk and other sub- 

 stances near the point of fermentation. But whether the 

 latter effects are due to the inductive action of the electricity 

 or the tremor produced by the thunder, has not to our 

 knowledge been definitel}' settled. If the effects are due to 

 induction, it is probable that they would be greater in the 

 case of milk in a metallic pan resting on the earth, than in 

 one of glass, supported on glass legs or on a thick cake of 

 bees-wax. 



Precautions with regard to lightning. — Men have often been 

 struck by lightning in open plains, and since the human 

 body is a good conductor of electricity, from the principles 

 above stated it must be evident that when standing it 

 would be more likely to be struck than any point on the 

 earth in the vicinity. There is less danger in a horizontal 

 position, particularly if the person be resting on some non- 

 conducting substance which would prevent the natural elec- 

 tricity from descending into the earth. Near the foot of a 

 tall isolated tree is always considered a dangerous position, 

 and this is in accordance not only with facts but well-estab- 

 lished principles. The upper part of the tree being a par- 

 tial conductor, particularly if covered with foliage, will be- 

 come electrified by induction, will attract the discharge to 

 itself, and in the passage of the lightning toward the earth 

 it will act with energetic induction on all surrounding objects, 

 and since the body of the man is a better conductor than ^ 

 the wood, the instantaneous inductive effect of the de- 

 scending bolt will be greater on the head of a man than 

 on the remaining part of the tree, and hence it will 

 diverge from the line it was pursuing, break through the 

 air, and pass through the body of the man. To attempt 

 to explain this phenomenon by merely saying that the elec- 

 tricity leaves the tree because the human body is a better 



