Intelligence and Miscellaneous Articles. 421 



between the edges of two chimneys and the photographic apparatus, 

 and found it to be 2° 46' 55". By means of a cathetometer the 

 distance of corresponding parts of the flash and of the lateral 

 spectra, and the distance of the edges of the chimneys, were mea- 

 sured. The first magnitude was 1*6 mm. and the second h"l. 

 From these data the angle of diffraction is calculated at C, S5'J, 

 and the wave-length at 382 . 10~ 6 mm. The determination of the 

 angle of diffraction is independent of a knowledge of the focal 

 distance of the object-glass, and of possible misdrawing. 



This measurement is not accurate enough to determine to what 

 body this line belongs ; it can only be concluded from this that 

 that portion of the light which is chiefly effective in photographing 

 lightning-flashes has approximately the wave-length 382 . 10~ 6 . 



This communication has been made with a view of inciting other 

 observers, who have at their disposal better apparatus and can more 

 frequently observe storms, to make experiments by this method. 

 It is possible that additional ultra-violet lines may be established 

 if we succeed in photographing flashes at several hundred metres 

 distance, for in the present case the distance of the storm was 

 more than 10 km. 



Measurements of the wave-lengths of lines of the spectrum of 

 lightning have been made by A 7 ogel and by Schuster, by means 

 ot a spectrum apparatus provided with a slit. The following 

 table gives the wave-lengths arrived at in their experiments : — 



Schuster. 



H. C. Vogel 



568-1 





559-2 





533-4 



534-1 



526-0 





518-2 



518-4 



500-2 



500-2 



486-0 

 458-3 

 467-3 



To this must be added one in the ultra-violet part of the spectrum 

 of the approximate value of 382 . 10~~ 6 . — Wiedemann's Annalen, 

 Feb. 1894. 



ON THE MAGNETIZATION OF SOFT IRON. 

 BY M. P. JOUBIN. 



In a note in the number of this Journal for last month I have 

 shown that we may expect to find a characteristic equation of the 

 intensity of magnetization of strongly magnetic bodies as a func- 

 tion of the susceptibility, and I proposed to verify this conclusion 

 experimentally. But the experiments of Kowland * solve this 

 question, at any rate for the bodies investigated by him, and which 

 comprise different varieties of iron, steel, and nickel. 



* Phil. Mag. 4th series, vol. xlvi. p. 140. 

 Phil. Mag. S. 5. Vol. 37. No. 227. April 1894. 2 F 



