Intermittent Lightning -Flashes. 107 



with whom I have since spoken have informed me that they 

 had observed a similar effect, and that in some instances 

 flashes, following as nearly as could be seen in the same path, 

 were separated by an appreciable interval, often of several 

 seconds' duration. Photographs of lightning have frequently 

 been obtained showing banded, ribbon, or double flashes; 

 bat, so far as I am aware, these have not been of so decided 

 a nature as to remove doubts whether the appearances could 

 not be ascribed to the effects of halation by reflexion from 

 the back of the negative, or to blurring from the photograph 

 having been taken through the glass of a window, or to some 

 other similar cause. I was therefore anxious to obtain some 

 decisive evidence of the repetition of the flashes, and as my 

 friend Mr. Gr. J. Snelus was at my suggestion attempting to 

 obtain some photographs of the lightning, I joined him, and 

 he kindly placed his camera and some plates at my disposal. 



The rain having ceased for the moment, I was able to go 

 out on to a balcony and thus get a good view of the storm, 

 which had now approached quite close and seemed to surround 

 us. The camera was held in the hand and pointed towards 

 the north-east, where, about half a mile away, numerous 

 brilliant flashes were occurring. The cap of the camera was 

 taken off, and then the camera was moved in a horizontal 

 plane about the lens as a centre at the rate of about once to 

 and fro in three quarters of a second, until a flash was observed 

 in the direction in which it was pointed, when the cap was 

 at once replaced. The duration of the exposure of the plate 

 was about half a minute. The camera was of quarter-plate 

 size, the plates were Ilford rapid, and the lens, which was a 

 rapid rectilinear, was used with full aperture ( //8). 



I hoped, by having the camera moving, to be able to separate 

 the successive components of the flashes, and in this I was 

 fortunately successful. In fig. 1 (PL IV.) is a reproduction of 

 one of the photographs obtained, and on it can be seen two 

 triple flashes (I., II., III., and IV., V., VI,), and one double 

 flash (VII. and VHP). 



During the interval that the plate was exposed the illumina- 

 tion of the sky from flashes out of the line of view, or behind 

 clouds, produced the glare seen in the centre and upper part 

 of the photograph, and some faint flashes which were noticed 

 were probably the cause of the streaks seen in fig. 2 at o, p, 

 and r. 



A careful examination of the photograph reveals many 

 interesting features. The three successive flashes I., II., III. 

 are identical in form. If the negative be placed over a print 

 so that either of the three lines on the negative lies over 



