152 MEMORIAL OF JOSEPH HENRY. 



thai when a discharge of a battery of several Leyden jars was sent 

 through the wire before mentioned, stretched across the campus in 

 fronl of Nassau Hall, an inductive effect was produced in a parallel 

 wire, the cuds dl' which terminated in the plates of metal in the 

 ground in the back campus, at a distance of several hundred feel 

 from tlic primary current, the building of Nassau 1 [all intervening. 

 The effect produced consisted in the magnetization of steel needles. 

 In this series of investigations, the fact was discovered that the 

 induced current, as indicated by the needles, appeared to change its 

 direction with the distance of the two wires, and other conditions 

 nt' the experiment, the cause of which for a long time baffled 

 inquiry, but was finally satisfactorily explained by the discovery 

 that the discharge of electricity from a Leyden jar is of an oscil- 

 latory character, a principal discharge taking place in one direction, 

 and immediately afterward a rebound in the opposite, and so on 

 forward and backward, until the equilibrium is obtained. 



V . The next series of investigations related t" atmospheric induc- 

 tion. The. first of these consisted of experiments with two large 

 kites, the lower end of the string of one being attached to the 

 upper surface of a second kite, the string of each consisting of a 

 fine wire, the terminal end of the whole being coiled around an 

 insulated drum. I was assisted in these experiments by Mr. 

 Brown, of Philadelphia, who furnished the kites. When they 

 were elevated, at a time when the sky was perfectly clear, sparks 

 were drawn of surprising intensity and pungency, the electricity 

 being supplied from the air, and the intensity being attributed to 

 the induction of the long wire on itself. 



VI. The next series of experiments pertaining to the same class, 

 was on tin' induction from thunder clouds. For this purpose the 

 tin covering of the roof of the house in which I resided was used 

 as an inductive plate. A wire was soldered to the edge of the roof 

 near the gutter, was passed into my study and out again through 

 holes in the window-sash, and terminated in connection with a plate 

 of metal in a deep well immediately in front of the house. By 

 breaking the continuity of that part of the wire which was in the 

 study, and introducing into the opening a magnetizing spiral, 

 needles placed in this could be magnetized by a flash of lightning 



