4 L. VEGARD. M.-N. Kl. 



I. is a quarz-spectrograph with a fairly large dispersion and of high light 



power, for studying the ultra violet part of the spectrum. 

 II. is a fairly big glass-spectrograph with a considerable dispersion and 



a fairly high light power. 

 III. is a small glass-spectrograph with the largest possible light power, but 



with a much smaller dispersion. 



The spectrographs I and II were especially designed for an accurate 

 determination of the wave length of the lines that might appear in the 

 auroral spectrum during the time of exposure which had to be very long. 



The small glass-spectrograph. III, was constructed for the study of 

 possible variations of the auroral spectrum, and also to learn how many lines 

 could be observed in the visible part of the spectrum. 



The big spectrographs I and II were mounted in a wooden box where 

 the temperature could be regulated automatically. The whole box could 

 be turned about a horizontal and a vertical axis. 



These spectrographs have been in operation during the last winter 

 (1922 — 23), and in this work I have been very ably assisted by mr. Einar 

 TøNSBERG. — We have already obtained a number of plates showing a 

 considerable number of lines. The plates have been measured at the 

 Physical Institute of Christiania, and in this work I have been ably assisted 

 by mr. Jonathan Aars. 



With the Quartz spectrograph we have obtained three spectrograms 

 taken on "Imperial Eclipse" plates. The time of exposure and the lines 

 obtained are given in table 1. 



It appears that with a time of exposure of 15 — 20 hours of north- 

 light a considerable number of lines can be obtained on the plate by means 

 of the Quartz spectrograph. It should be noticed that in the spectra 1 and 

 2 the strongest lines, such as 4278 and 3914, are over-exposed. 



To give an idea of the relative strength of the lines I have given 

 them intensities from 1 — 10. Later on I intend to give more accurate 

 intensity-values based on quantitative measurements with a registering micro- 

 photometer. 



On the spectrograms from the Quartz spectrograph 21 lines have been 

 measured. 



With the big glass spectograph we at first used an Imperial pancro- 

 matic plate B. This plate was developed after an exposure of 20 hours 

 of northlight, but the plate showed only the green auroral line. The He- 

 spectrum was used for comparison. The measurements gave for the auroral 

 line the following wave length : 



/ = 5578,2 ' (int. units). 



' The accuracy may be somewhat reduced trough over exposure of the comparison 

 spectrum. Since this was written the auroral line was obtained on a plate with very 

 sharp lines, and which gave X = 5577,2 int. units. 



