ii.] ORIGIN OF THE LINKS. 19 



This experiment quite convinced Fraunhofer that interference 

 would not account for the dark lines, and he was soon able to 

 announce that 



" Various experiments and changes to which I have submitted 

 these lines convince me that they have their origin in the nature of 

 the light of tJie sun, and that they cannot be attributed to illusion, 

 to aberration, or any other secondary cause." l 



He then states that he applied this method to the examination 

 of the spectra of Venus and certain stars, " without allowing 

 the light to fall on a small aperture." Here we have Fraunhofer 

 introducing a method of observation of stellar spectra that is 

 still the one employed in our own times. 



He was rewarded by being enabled to make the following 

 observations on the spectrum of Venus : 2 



" In the spectrum formed by this light, I found the same lines 

 such as they appeared in the light of the sun. That of Venus, 

 however, having little intensity compared with that of the sun 

 reflected from a mirror; the brightness of the violet and the 

 exterior red rays is very feeble. On this account we perceive even 

 the strongest lines in these two colours with some difficulty ; but 

 in the other colours they are easily distinguished. I have seen the 

 lines D, E, 6, F (Fig. 6) very well terminated ; and I have re- 

 cognised that those in b are formed of two, namely, a fine and a 

 strong line. The weakness of the light, however, prevented me 

 from seeing that the strongest of these two lines consisted of two ; 

 and, for the same reason, the other finer lines could not be dis- 

 tinguished. By an approximate measure of the lines D E and E F, 

 I am convinced that the light of Venus is, in this respect, of the 

 same nature as that of the sun." 



Then, coming to the stars : 



" With the same apparatus I have also made several observations 

 on some of the brightest fixed stars. As their light was much 



1 Eclin. Phil. Journal, vol. x. p. 38. 



2 Ibid. vol. ix. p. 298. 



C 



