1837] WRITINGS OF JOSEPH HENRY. 103 



In one experiment described a copper wire one-eighth of an 

 inch in diameter was plunged at its lower end into the water 

 of a deep well, so as to form as perfect a connection with the 

 earth as possible. A small ball being attached to the upper 

 end and sparks passed on to this from the globe before men- 

 tioned a lateral spark could be drawn from any part of the 

 wire, and a pistol of Volta fired even near the surface of the 

 water. This effect was rendered still more striking by attach- 

 ing a ball to the middle of the perpendicular part of a light- 

 ning rod, put up according to the directions given by Gay- 

 Lussac. When sparks of about an inch' and a half in length 

 were thrown on the ball corresponding lateral sparks could 

 be drawn not only from the parts of the rod between the 

 ground and the ball, but from the part above even to the 

 top of the rod. Some remarks were then made on the theory 

 of thunder-storms, as given by the French writers, in which 

 the cloud is considered as analogous in action to one coating 

 of a charged glass, the earth the other coating, and the air 

 between as the non-conducting glass. One very material 

 circumstance has been overlooked in this theory, namely, 

 the great thickness of the intervening stratum and the con- 

 sequent great quantity of free or redundant electricity in 

 the cloud. This must modify the nature of the discharge 

 from the thunder-cloud, and lead to doubt if it be perfectly 

 analogous to the discharge from an ordinary Leyden jar, 

 since the great quantity of redundant electricity must pro- 

 duce a comparatively greater lateral action; and hence, pos- 

 sibly, the ramifications of the flash and other similar phe- 

 nomena may be but cases of the lateral discharge. 



Some facts were then mentioned on the phenomena of the 

 spark from a long wire charged with common or atmospheric 

 electricity. It is well known that the spark in this case is 

 very pungent, resembling a shock from a Leyden jar. The 

 effect does not appear to be produced, as is generally sup- 

 posed, by the high intensity of the electricity at the ends of 

 the wire by mere distribution, since this is incompatible 

 with the shortness of the spark. In one experiment fifteen 

 persons, joining hands, received a severe shock, (while stand- 



