1889.] of the various Species of Heavenly Bodies. 219 



probably the same lines, that it is somewhat difficult to assign 

 origins for the lines. These discrepancies occur not only in the 

 measures made by different observers, but in those made at different 

 periods by the same observer. Further, the individual observations 

 are seldom recorded, but in place of them are given the means of 

 several observations, and in some cases the means have been obtained 

 by throwing together lines which are very far apart. At best, there- 

 fore, it is only possible to suggest the most probable origins of the 

 lines and bands seen. 



The object of the present paper is therefore mainly to direct further 

 inquiries. 



I. EARLY OBSERVATIONS. 

 Angstrom's First Observations. 



The spectroscope was employed in investigating the nature of the 

 aurora spectrum by Angstrom in 1867.* He found that the light was 

 almost perfectly monochromatic, the spectrum consisting mainly of a 

 yellow-green line at a wave-length given by him as 5567. With a 

 wide slit other faint bands were visible. 



The note is so short that I give it in full; translated it reads 

 thus : 



" From the time of Franklin's memorable observations on elec- 

 tricity up to the present there has been a perfect agreement 

 between the actions of this natural force and those of frictional elec- 

 tricity, that it was easy to foresee that the spectrum of lightning 

 must be the same as that produced by the ordinary electric discharge 

 in air. The observations made by M. Kundt have perfectly proved 

 this. The two phenomena of the aurora borealis and of terrestrial 

 magnetism being so closely connected with each other, that the 

 appearance of the aurora is always accompained by disturbances of 

 the magnetic needle, it might be supposed that the aurora borealis 

 was only an electric flash, which is however not the case. During the 

 winter of 1867-68 I was able several times to observe the spectrum of 

 the luminous arc which borders the dark segment, and is always 

 present in faint auroras. Its light was almost monochromatic, and 

 consisted of one bright line, on the left of a group of calcium lines. 

 I determined the wave-length of the line which was equal to A> = 

 5567. Beyond this line the intensity of which is relatively great, 

 I observed also, by increasing the width of the slit, traces of three 

 very faint bands which extended almost to JB 1 . On one occasion only, 

 where the luminous arc was agitated by undulations which changed 

 its form, I saw the regions in question lighted momentarily by some 

 faint spectral lines ; but considering the lack of intensity of the 

 * ' Spectre Normal du Soleil,' 1868, p. 41. 



