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POPULAR SCIENCE MONTHLY. 



round to avoid doing this. The arrangement adopted, when it is 

 desired to obtain both positive and negative discharges simul- 

 taneously on the same 

 plate, and when connect- 

 ing sparks from positive 

 to negative are desired, 

 is similar, only in these 

 cases the two discharg- 

 ing points are placed on 

 the film side of the plate. 

 Many very beautiful 

 photographs of light- 

 ning flashes have been 

 made. They are not at 

 all difficult to get. It is 

 only necessary to wait 

 for a suitable stormy 

 night, point the camera 

 containing the sensitive 

 plate in the direction of 

 the storm, remove the 

 cap, and await the flash. 

 The photographer of 

 lightning flashes is some- 

 times startled to obtain 

 in his finished picture 

 streaks of lightning, 

 some white and others 

 black, the latter being 

 produced by the flashes 

 which were so actinic as 

 to produce upon the sen- 

 sitive film the phenome- 

 non known as " reversal." 

 One of the most in- 

 teresting photographs of 

 lightning flashes that I 

 have seen is that repro- 

 duced above. It has been 

 kindly sent to me by 

 Prof. Ch. von Zenger, the 

 renowned meteorologist. It was made on May 20, 1894, when a 

 terrific storm, of short duration fortunately, broke over the town 

 of Prague. The lightning depicted in the photograph struck four 

 houses at once, doing considerable damage. It will be noticed 

 that descending from the clouds are six discharges ; one flash can 



