392 WRITINGS OP JOSEPH HENRY. [1855- 



much familiarity with them. The effect of the rod in this 

 case on the surrounding air and on the cloud itself by invis- 

 ible induction must have been quite remarkable. 



Action of lightning-rods. — The question as to whether the 

 lightning-rod actually attracts the electricity from a distance 

 has been frequently discussed. "It will be found," says Sir 

 W. Snow Harris, " that the action of a pointed conductor is 

 purely passive. It is rather the patient than the agent ; and 

 such conductors can no more be said to attract or invite a 

 discharge of lightning than a water-course can be said to 

 attract the water which flows through it at the time of heavy 

 rain." This statement does not, as it appears to us, present 

 a proper view of the case. From the established principles 

 of induction, it must be evident that all things being equal 

 a pointed rod, though elevated but a few feet above the 

 ground, would be struck in preference to any point on the 

 surface, and the propositions as to the space which can be 

 protected from a discharge of lightning are founded on the 

 supposition that the direction of the discharge can be changed 

 by the action of the rod at a distance and the bolt drawn to 

 itself. The true state of the case appears to us to be as fol- 

 lows: 



1st. An elevated pointed rod, erected for example on a 

 high steeple, by its powerful induction diminishes the in- 

 tensity of the lower part of the cloud, and therefore may 

 lessen the number of explosive discharges to the earth. 



2d. If an explosive discharge takes place from the cloud 

 due to any cause whatever, it will be attracted from a giver 

 distance around to the rod, and transmitted innoxiously to 

 the earth. 



A too exclusive attention to either one or the other of these 

 actions has led to imperfect views as regards the office of 

 the lightning-rod. On the one hand, some have considered 

 that the whole effect of the rod is to lessen the number of 

 discharges in the way described, and have considered 

 it impossible that an explosive discharge could take place 

 on a pointed conductor. But this is not the case, as was 

 shown by Mr. Wilson many years ago by his experiments 



