1878] WRITINGS OF JOSEPH HENRY. 5^ 



when a neutralization would suddenly take place, sufficient 

 to produce through nervous influence — the phenomena wit- 

 nessed. The shock received by the person in his foot on 

 getting out of bed is in direct accordance with the well-es- 

 tablished principles of induction. So long as the body was 

 in a horizontal position in the bed, which is only a partial 

 conductor, the inductive effect would be much less on it than 

 on the wet floor and iron pillars. When the foot therefore 

 approached the floor, a positive charge would pass from the 

 latter to the former. 



That any physiological effects should have been observed 

 under the conditions in which the observers were placed 

 could scarcely, from a pnoriJ considerations, have been antic- 

 ipated. They were in a space entirely enclosed by metallic 

 conductors, with the exception of the floor, and in such a 

 condition it might be thought that they would have been 

 completely protected, since the interior of a hollow vessel, 

 (like that of a quart measure,) when insulated and charged, 

 gives no indication of electricity. If a metal ball is sus- 

 pended by a silk thread, and made to touch the interior of 

 such a vessel charged exteriorly, and afterward transferred 

 to a delicate electrometer, no sign of electricity is observed. 



It should be remembered however that in the case of the 

 experiment just mentioned the statical charge of electricity 

 is nearly uniformly distributed over the sides and bottom of 

 the vessel ; whereas, in the case of a dynamic charge, the 

 electricity may pass in greater quantity on one side than 

 on another, and the equilibrium of the interior may not be 

 preserved ; or furthermore, in this case the diameter of the 

 house being more than twice as great as its vertical height, 

 it would be represented in the preceding experiment by a 

 very shallow vessel in which a complete neutralization could 

 not take place. But whatever may be the explanation of the 

 phenomena, the facts stated are of importance in the theoreti- 

 cal consideration of the action of lightning protection. 



With thanks for the honor conferred upon me by my 

 election as a member of the American Electrical Society, 

 I remain, very truly, &c., &c. 



