A LIGHTNING SPIRAL OBSERVED NEAR BASEL." 



By Fh. Klincei.I'Uss. 



On the night of July 15, 1!)()2, hctweeu 11 and 12 o'clock, I 

 obtained, in a fixed camera, a photograph of a very extraordinary 

 lightning phenomenon. The Hash occui-red in an east-southeast di- 

 recti(m. as viewed from the center of the city of Basel, and extended 

 nearly horizontally from north toward south, or, as shown in figure 

 1. i)late 1, from left toward right. Not all the details seen in the 

 photograph could be recognized l)y the eye, nor could I determine 

 the distance fi-om my standpoint to the scene of the discharge, 

 because of the simultaneous sound of tliunder from another flash. 

 As the lens of the camera was uncovered for this exposure only a 

 few seconds, it is probable that all that is shown in the illustration 

 represents l)ut one discharge. 



Fx'sides a j)encil of ])arallel rays (caused probably by partial dis- 

 charges torn ai)art by wind currents), such as is familiar from the 

 photograph of II. Kayser,'' the plate which is here shown contains 

 two vei-y distinct whirls of bright lines and a third fainter one. In 

 addition there may be recognized a great numl)er of bright lines 

 running parallel to the axis of these spirals. Within the pitch of 

 a single line of the spiral 50 or GO parallel lines may be counted. 



Inasmuch as a similar screw-shaped formation may be observed 

 under certain conditions in the discharge of an induction coil, it 

 seems highly probable that we have here to do with a spiral light- 

 ning discharge. Thus when a very great quantity of electricity is 

 discharged with the bluest possible sparks and without strong aureole 

 or arc there are produced magnificent spirals.'' Figure 2, plate i, 

 shows an instantaneous exposure of about 0.05 second duration on 

 such a discharge from an induction coil giving sparks 50 cm. long. 

 The greater the quantity of electricity in the discharge the .more 



"Translated by permission from Annalon der Physilc, Leip/Jg, No. 1. 190.3. 



h.H. Kayser, Wled. Ann. 2;"), p. i;n, 18.sr>. 



(• K. Rulnuer. Elelvtrotechn. Zeitsclir. 21. p. 1,"L', 1<M)0. 



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