588 POPULAR SCIENCE MONTHLY. 



lie ill a plane, but was concave toward a point at the observer's 

 left. That the ribbon did not stand at right angles with the line 

 of sight, bnt was nearer the observer at the right-hand edge, is also 

 shown by the inequality of the lower termination of the six vertical 

 lines referred to above. The ones at the left either rest upon or 

 are hidden behind a rise of ground, whose crest can be traced for 

 a little distance each side of the flash, while those at the right come 

 lower, falling between the observer and the ground at that point. 

 Probably, when measured upon this diagonal and curved line, the 

 width of the Hash was fifteen or twenty feet. 



Mention has already been made of the fact that the accom- 

 panying thunder was comparatively light, and not at all like that 

 ordinarily heard when lightning occurs within so short a distance. 

 Possibly this, as well as the absence of marks at the point where 

 it reached the earth, might have been because the discharge was 

 of very low tension. 



[A very similar lightning flash was described and pictured in 

 the issue of the Electrical World and Engineer for October 28, 

 1899, by A. E. Kennelly, who suggested the following explanation: 

 A lightning flash passed through the air on the left-hand side of 

 the ribbon of lightning (the wind was blowing from right to left) 

 and broke a hole in the air along that line. This discharge may 

 have been oscillatory, and may have lasted in. all any time up to 

 about y^o" of a second. The discharge then ceased for lack of 

 electricity, but a fresh charge from the cloud being gathered imme- 

 diately afterward, or in about ^^ of a second from the first rup- 

 ture, a new discharge passed through the same hole in the air, 

 which had not had time to seal up. There might thus be fourteen 

 successive flashes (this Avas the number of distinct flashes making 

 up the ribbon in the photograph), each averaging about ^^ of a 

 second apart, through the same hole, owing to the imperfect con- 

 ducting qualities of the clouds overhead, meanwhile the hole hav- 

 ing been carried from left to right in the picture, across the line 

 of sight (by the wind), and thus producing the appearance of a 

 broad ribbonlike flash. Professor Trowbridge, of Cambridge, has 

 suggested the possibility that many of these apparently curious 

 electrical phenomena may be of purely optical or physiological 

 origin — that is, may arise through the abnormal behavior of the 

 eye or the camera lens toward intense lines of light, such as light- 

 ning flashes. — Ed.] 



