Page:St. Nicholas, vol. 40.1 (1912-1913).djvu/665

1913.]

In photograph No. 2, if the camera was stationary while the exposures were made, the two flashes which show double and treble are what are commonly called “ribbon flashes.” This ribbon effect can probably be accounted for in this way: we know that most flashes are multiple. By moving the camera, this fact is shown. It is possible that the wind, if strong, may push, and so shift somewhat, the path left by the first discharge, and, when other discharges occur, they will follow this path and so seem to be at a little distance from the place at which the first discharge took place.



No. 3 shows a mass of streaks, some of them appearing black. In this instance, I am positive that we have a plain case of “reversal,” that is, when a bright object appears as dark on the negative. We can cause reversal of the image in several ways, for example by photographing a spark from a static electric machine, and after it has been impressed on the plate, opening the shutter for an instant in a subdued light. We will then find, on developing, that the image of the spark has been reversed and shows black. In the case of this picture, the flashes which show black were the first which took place, and would have shown white if subsequent flashes had not appeared, or if the shutter had been closed before they came. As it was, these after-flashes acted like the after-light men- tioned as causing the reversal of the image of the spark from a machine.



No. 4 is a puzzle. It appears to have been caused by accidental light which entered the camera; but I should not like to give any positive opinion on the matter. I am in possession of a picture of lightning taken by myself which shows almost like the curved streak on this picture, and almost as broad. It is not in the foreground as this is, but in the sky, as are other flashes.—.

Mr. Larsen has had extensive experience in photographing lightning by a variety of methods. The average observer would say that No. 4 represented merely some accident to the plate, as our critic first suggests.— Rh