British Association for the Advancement of Science. 17 



communicated ; but when thrown on in the form of a spark, it is 

 dissipated as before described. Other facts of the same kind were 

 mentioned ; and also, that we could take advantage of the princi- 

 ple to produce a greater effect in the decomposition of water by 

 ordinary electricity. The fact of a wire becoming luminous by a 

 spark, was noticed by the celebrated Van Marum more than fifty 

 years ago, but he ascribed it to the immense power of the great 

 Haarlem machine. The effect, however, can be produced, as be- 

 fore described, by a cylinder of Nairn's construction, of seven 

 inches in diameter, a globe of a foot in diameter being placed in 

 connexion with the prime conductor to increase its capacity. 



Some experiments were next described, in refer- 

 ence to the induction of the lateral action of dif- 

 ferent discharges on each other. When the long 

 wire is arranged in two parallel, but continuous 

 lines, by bending the wire, the outer side of each 

 wire only becomes luminous ; when formed into 



three parallel lines by a double bend, the middle ^ 

 portion of the wire does not become luminous, the outer sides only 

 of the outer lines of wire exhibit the rays. When the wire is 

 formed into a ffat spiral, the outer spiral alone exhibits the lateral 

 discharge, but the light in this case is very brilliant j the inner 

 spirals appear to increase the effect by induction. 



Prof. Henry then stated, that a metallic conductor, intimately 

 connected with the earth at one end, does not silently conduct 

 the electricity, thrown in sparks, on the other end. In one ex- 

 periment described, a copper wire, ^th of an inch in diameter, 

 was plunged at its loAver end into the water of a deep well, so as 

 to form as perfect a connexion with the earth as possible ; a small 

 ball being attached to the upper end, and sparks passed on to this 

 from the globe before mentioned, 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 attaching a ball to the middle of the perpendicular 

 part of a lightning 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. 



Vol. XXXIV.— No. 1. 3 



