PHOTOGRAPHING LIGHTNING WITH MOVING CAMERA. 



125 



Figure T shows the spectrum of one of those horizontal meandering 

 flashes often seen at the conchision of a storm of long duration. It 

 was obtained September 1, 1005. It diifers considerably from figures 

 6 and 8, several lines being absent. The first line of this spectrum is 

 probably the same as the eighth line of the spark spectrum. 



No definite opinion can at present be offered by the Avriter as to the 

 meaning of these changes of the lines in the spectra of dilierent 

 flashes; more material must be obtained before a positive statement 

 can be made. 



Below is a table of measurements of the three spectra and their 

 l^robable relations. Several measurements have been taken, and the 

 average are here presented . 



(iBand. 



!> Double. 



It may not l)e out of place here to give a fcAV brief hints as to the 

 best method for obtaining lightning photographs, for the benefit of 

 the large number of amateur photographers scattered over the world. 

 Thunder storms are nearly alwaj^s cyclonic in their character, their 

 diameter varying. When they extend over large areas it will usually 

 be found that most of the vertical flashes are at the circumference of 

 the circle through which the storm is passing. In the central part of 

 a storm the flashes are usually horizontal, or j^assing between two 



