LIGHTNING.
Barg, ARAB. I Skimshek, . . . TURK.
Bijli, HIND. .
Sheet-lightning is an electric phenomenon very common in India; it is unaccompanied by thunder, or is too distant to be heard. When it appears, the whole sky, but particularly the horizon, is suddenly illuminated with a flickering flash. The zigzag appearance is often observed. Philo sophers differ much as to its cause. Matteucci supposes it to be roduced either during evapora tion, or evolved according to Pouillat's theory) in the process of vegetation ; or generated by chemical action in the great laboratory of nature, the earth, and accumulated in the lower strata of the air in consequence of the ground being an imperfect conductor. Arago and Kamtz, how ever, consider sheet-lightning as reflections of distant thunder-storms. Saussure observed sheet lightning in the direction of Geneva, from the Hospice du Grimsel, on the 10th and 11th of July 1783 ; while at the same time a terrific thunder-storm raged at Geneva. Howard, from
Tottenham, near London, on July 31, 1813, saw sheet-lightning towards the south-east, while the sky was bespangled with stars, not a cloud float ing in the air ; at the same time a thunder-storm raged at Hastings, and in France from Calais to Dunkirk. Arago supports his opinion, that the phenomenon is reflected lightning, by the follow ing illustration. In 1803, when observations were being made for determining the longitude, M. de Zach, on the Brocken, used a few ounces Of gun powder as a signal, the flash of which was visible from the Klenlenberg, sixty leagues off, although these mountains are invisible from each other.— Cosmos ; Curiosities of Science; Collingwood.