744 



THE AURORA BOREALIS. 



The following table contains the measurements made by 

 Lieutenant Parent. 



1872. 



•• 



2. 3. 



4. 



5. 



6. 



7. 



8. 



November 3 





527-84 









4-1-50 





424 -Gi 







528 



47 









467-80 



.. 





„ „ 





. 











471-79 



,. 





» » 















470-17 





., 



4 





527 



84 









472-30 







8 





, 





522-39 





487-37 



471-79 





430-89 

















472-30 





430-76 



» » 





. 











472-72 



.. 





29 





. 











468-98 



,, 



, ^ 





.. 













489-27 





,. 



December 5 





• 





519-05 



•• 





•• 



•• 



•• 



Mean 





528 



05 



520-72 





487-37 



470-87 





428-76 



Probable Error - 





+ 0-14 



+ 1-11 



.. 





+ 0-54 



, , 



+ 1-68 























[Seeing that the results obtained by Lieutenant Parent are so 

 near to those obtained by Mr. Wijkander, it seems probable 

 that they are quite trustworthy. If we take the mean of all the 

 results we get : 



Mean, 535-9, 528-6, 523* 1,499-6, 487-2,470-1,436-6,428-4.] 



In these last experiments the crossed spider lines were not 

 placed very exactly in the focus of the eye-piece, and so these 

 have been omitted in making the final determination of wave- 

 lengths. But the agreement between the two sets of observations 

 shows the accuracy of the results. 



' The appearance of the Aurora was often observed on other 

 days with this spectroscope, when the light was too faint to admit 

 of measurement. With every appearance of the Aui-ora, the rays 

 have always been visible, except 4, 5, and 7. These have been 

 seen several times, but have often been wanting, not entirely from 

 the faintness of the light, but probably from some change in the 

 nature of the electric discharge, still in that case no indications 

 have been found as to the conditions of this irregularity. 



Between the rays 2 and 3 there are probably smaller lines, 

 which form with them a broad band of light of variable intensity. 

 In the same way the ray 6 spreads on the violet side of it into a 

 tolerably broad but somewhat indistinct band. After careful 

 search no red ray has been found, but at the same time no red 

 Aurora was ever seen in winter quarters. 



The following table contains the different measures of the lines 

 of the Aurora which have been made with the greatest accu- 

 racy : — 



Angstrom - 



.. 



55G-7 



.. 



.. 



.. 



521- 



501- 



487- 



472- 



.. 



.. 



., 



Vogel 



629-7 



557-1 



539-0 





523-8 



518-9 



500-4 



.. 



469-4 



.. 



.. 



.. 



Lemstrom - 



.. 



556-9 



.. 



.. 



523-5 



*- 



496-9 



.. 



469-4 



.. 



426-2 



411-2 



"Wijkander - 



•• 



557-2 



535-9 



528-9 



523-9 





499-6 



487 -3 



469-2 



436-6 



42S-0 



•• 



