LIGHTNING, PHOTOGRAPHING The first successful photograph of a lightning flash was taken on a dry plate on September 2, 1882. Lightning cannot be photographed during the daytime, as, however dark the sky is, the sun is behind it and actinic enough to have an action upon the dry plate, and make the flash invisible. At night the sky may be black and have no action upon the photographic plate, the flash appearing to stand out prominently. It is not advisable to photograph lightning through a closed window. Coming storms exhibit the best flashes, although at the seaside good flashes may often be obtained from storms disappearing seawards. The finest lightning photographs have been taken looking seawards, there being no obstructions between camera and horizon. The latter should always be included in the picture, as when taking clouds ; otherwise, in the photographs, it may not be easy to tell the top from the bottom of the flash. The camera must be supported, either by a stand or other means ; if it is of fixed focus, there will, of course, be no focusing necessary, but if of the focusing pattern, the lens should be racked out to the position it would occupy if a distant view were being photographed. It is desirable to focus during the day and to make a mark on the baseboard, so that the focus may be instantly ascertained at night, when accurate focusing is impossible. Having made all ready and fixed the camera with the lens pointing in the direction of the flashes, the dark-slide is inserted, the shutter drawn, the plate exposed, and the flash waited for ; when it does appear, providing that it is within the range of the lens, it photographs itself ; the lens is then capped and the plate changed. It is advisable to use wide
angle lenses so as to include as much of the sky as possible, as forked lightning has a way of disappearing from a narrow field of view. The largest possible stop should be used, and a rapid plate, well backed so as to prevent hala tion. Detail is not so much wanted as contrast in the negative, and development should there fore not be continued long enough to produce fog, as a flash showing but faintly on a negative may easily be intensified, preferably with mer cury and ammonia. One developer is as good as another for negatives of this class, but hydro quinone and a mixture of hydroquinone and metol appear to be the favourites. The plate should be changed after every flash photographed, no matter of what kind ; one may be unfortunate enough to expose a dozen or more plates on weak sheet flashes, which are useless photographically, while, on the other hand, one may be fortunate in securing a forked flash every time. Sheet lightning will fog a plate and make it quite use less.