Popular Science Monthly/Volume 56/March 1900/Ribbon Lightning

From Wikisource
Jump to navigation Jump to search



IN the summer of 1898, W. H. Osborne, of Chardon, Ohio, an amateur photographer of some experience, secured the accompanying photograph of a lightning flash which seemed to us to show certain peculiarities that entitle it to a public notice and a permanent record. The picture shows three flashes, of which the distant and faint one at the right and the bright one at the left were simultaneous, while the center one occurred a few seconds earlier. Nothing about the thunder that followed the last and bright flash suggested that it was specially near, but an examination of the picture when developed and a comparison with the features of the landscape showed that it had come to earth about fifteen rods from the place where Mr. Osborne stood with his camera. Mr. Osborne

PSM V56 D0603 Ribbon lightning.png

and myself carefully searched the locality indicated, but failed to find even the slightest mark caused by the discharge upon any object or in the earth.

Measurements at this place give the width of the ribbon of light, if it stood at right angles with the line of sight, about eight feet. This ribbon of light is seen to consist of six lines, approximately parallel, of unequal brightness, a pair being at each edge and a pair near the center. The space between these pairs is crossed by many nearly horizontal lines and a few oblique ones, while that between the right-hand pair is crossed by oblique lines only. The horizontal lines at the right of the center become curved downward, which, with the increased brightness of the whole toward that side, suggests to us that the ribbon of light did not lie in 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, but 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 flash was fifteen or twenty feet.

Mention has already been made of the fact that the accompanying 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 1/100 of a second. The discharge then ceased for lack of electricity, but a fresh charge from the cloud being gathered immediately afterward, or in about 1/30 of a second from the first rupture, 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 was the number of distinct flashes making up the ribbon in the photograph), each averaging about 1/25 of a second apart, through the same hole, owing to the imperfect conducting qualities of the clouds overhead, meanwhile the hole having 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 lightning flashes.—Ed.]