-1859] WRITINGS OF JOSEPH HENRY. 391 



feet from the surface of the ground, was melted, the dis- 

 charge was transmitted to the earth without any other effect 

 than a slight inductive shock given to a number of persons 

 standing at the foot of the tower. In three of these cases the 

 peculiar sound we have mentioned was observed; — first, a 

 slight hissing noise, and afterward the loud explosion, as if 

 the former were produced by the effect of the discharge on 

 the air in the immediate vicinity of the rod, and the loud 

 noise from that on the air at a more distant point of its path. 

 The writer was led to reflect upon this effect of the rod by 

 a remarkable exhibition he witnessed during a thunder- 

 storm at night in 1856. He was in his office, which is in 

 the second story of the main tower of the Smithsonian edifice, 

 when a noise above, as if one of the windows of the tower 

 had been blown in, attracted his attention : an assistant who 

 was present was requested to take his lantern and ascertain 

 what had happened. After an absence for some time he re- 

 turned, saying he could discover nothing to account for the 

 noise, but that he had heard a remarkable hissing sound. 

 The writer then ascended to the top of the tower, and stood 

 in the open trap-door with his head projecting above the 

 flat roof within about twelve feet of the point of the light- 

 ning-rod. No rain was falling, though an intensely black 

 cloud was immediately overhead and apparently at a small 

 elevation; from different parts of this, lightning was con- 

 tinually flashing, indeed the air around the top of the tower 

 itself appeared to be luminous. But the most remarkable 

 appearance was a stream of light three or four feet long issu- 

 ing with a loud hissing noise from the top of the lightning- 

 rod. It varied in intensity with each flash, and was almost 

 continuous during the observation. Although the whole 

 appearance was highly interesting, and produced a consider- 

 able degree of excitement, yet the writer did not deem it 

 prudent to expose himself to the direct or even inductive 

 effect of a discharge under such conditions, thinking as he 

 did with Arago, that however our vanity might prompt us 

 to boast of the acquaintance of some great lords of creation, 

 it is not always desirable to seek their presence or court 



