A LIGHTNING SPIRAL OBSERVED NEAR BASEL." 



By Fb. Kmngelfx «s. 



On the nio-ht of July ir>, li)Oi>, between 11 and I'i o'clock, I 

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

 lightninif phenomenon. I'he Hash occurred in an east-southeast di- 

 rection, as viewed from the center of the city of Basel, and extended 

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

 1, plate I, from left toward right. Xot all the details seen in the 

 photograph could be recognized by the eye, nor could I determine 

 the distance from my standpoint to the scene of the discharge, 

 because of the simultaneous sound of thunder from another Hash. 

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

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

 represerits but one discharge. 



Besides a pencil of parallel rays (caused probal)ly by ])artial dis- 

 charges torn apart by wind currents), such as is familiar frt)m the 

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

 two very distinct whirls of bright lines and a third fainter one. In 

 addition there may be recognized a great munber of bright lines 

 running parallel to the axis of these spii-als. Within the pitch of 

 a single line of the s])iral 50 or ()0 parallel lines may be counted. 



Inasmuch as a similar screw-shaped formation may be observ^ed 

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

 seems highly probable that we have here to do with a spii-al 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 



1 Translated by permission from Annalen der I'liysik. Leipzig, No. 1, WO'A. 



6H. Kayser, Wied. Ann. 2."i. p. iiU. ISS.".. 



cE. Ruhmer. Elel^trotechn. Zeitscbr. 21, p. 152, 1900. 



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