120 PHOTOGRAPHING LIGHTNING WITH MOVING CAMERA. 



The camera Avas moved by hand, being- swung from right to left 

 and back again, each swing histing about one second and covering an 

 angle of about ()0°, which was also the angle of the lens. The ap- 

 paratus employed was an ordinary magazine plate camera, which 

 for all ordinary purposes is the most convenient on account of the 

 rapidity with which the plates can be changed, this being of great 

 importance, because, as a rule, the time most favorable for obtaining 

 good pictures is very short, seldom lasting longer than from ten 

 to fifteen minutes. 



Several more pictures were obtained in 100?). The three most in- 

 teresting ones up to that year are shown in figures 1, 2, and 3. (See 

 plates.) Figure 1 shows a flash obtained on July 17, 1002. The dis- 

 charge took place between two clouds. It will be noticed that it is 

 composed of a mnnber of separate discharges (or rushes) and bands; 

 as many as thirty-four can be counted on the negative. As the flash 

 covers about half of the plate, and as the approximate speed of the 

 camera was about one second to cover the plate, or GO"^, it follows that 

 the approximate duration of this flash was about half a second. Fig- 

 ure 2 shows a flash obtained on July 11, 1003. This flash is interesting 

 for several reasons. It is composed of fourteen separate discharges, 

 the first one being the brightest, and having side branches pointing 

 downward, proving that the first discharge passed from the cloud 

 to the earth and that the resistance Avhich it had to overcome nuist 

 have been excessive (the side branches prove that). At a distance 

 of 3 millimeters from the first rush is another discharge following 

 the same path, but without side branches (what appear as such are 

 really branches from the first rush). At a distance of 12-5 milli- 

 meters from the last discharge will be seen two rushes '5 millimeter 

 apart, and from there for a distance of 10 millimeters are a series 

 of discharges close together, forming a broad l)and. The dark space 

 which divides this flash is a cloud through which the discharge is 

 passing. Another interesting fact about this flash is that the path 

 of it is spiral shaped, the motion is from right to left, or opposite to 

 the motion of the hands of a clock, looking downward from the 

 cloud. Figure 3 was obtained October 1, 1003. AVe have here a flash 

 composed, first, of two bright discharges close together, then there 

 appears to be an interval of about a fourth of a second, which in all 

 probability was filled in with a number of fainter oscillations (the 

 lines running across seem to indicate that), and at the conclusion 

 of the flash are four fairly bright rushes. 



In the summer of 1001 copies of -some of the photographs were 

 sent to the Smithsonian Institution for examination, and through the 

 suggestions and assistance of the experts of that Institution a new 

 method of moving the camera was devised. 



