Intermittent Lightning-Flashes. 109 



evident, however, that the series L, II., III. cannot have 

 occurred during the same sweep of the plate as IV., V., VI., 

 since the curve joining a, 5, c is concave upwards, while that 

 joining a, d, e is concave downwards. The flashes VII., VIII. 

 seem also to have formed part of the same system of dis- 

 charges, for the part of VII. from / to just above h is coin- 

 cident with the upper portion of I., while the luminous streaks 

 extending between VII. and VIII. agree in their directions 

 with the curves joining a, b, c and a, d, e, those at g being 

 parallel to the line joining d and e, and those at k following 

 nearly but not exactly the line of a, h, c. There is thus 

 afforded some clue to the determination of the order of 

 the discharges, and I think the order was probably as 

 follows:— VII., VIII., VI., V., IV., I., II., III., the first 

 two occurring during one sweep of the camera ; VI., V., IV. 

 during the backward sweep ; and I., II., III. in the next 

 onward sweep. There must thus have been an interval of 

 a little over a second between the first and last discharge, for 

 the motion of the camera was at about the rate of three 

 quarters of a second for a complete swing to and fro. The 

 interval between the successive discharges was, therefore, be- 

 tween the fifth and tenth of a second. Had it been much 

 longer the flash would have presented to the eye a flickering 

 appearance. 



Whatever be the explanation of some of the effects noticed 

 above, it is evident that a lightning flash has not the simple 

 instantaneous character formerly supposed ; but that it con- 

 sists of a varying number of successive discharges following 

 one another in the same path at intervals which may in some 

 cases be comparatively long. 



Note. — Since the above was written I have had an oppor- 

 tunity of inspecting the photographs of banded, ribbon, and 

 curtain lightning collected by the Royal Meteorological 

 Society. There is, I think, no doubt that the explanation of 

 these is afforded by the multiple flashes and luminous streaks 

 noticed above. It is noteworthy that they were always ob- 

 tained with a camera held either in the hand or in such a way 

 as to render motion probable. 



Science Schools, S. Kensington. 



Phil. Mag. S. 5. Vol. 28. No. 171. August 1889. K 



