ii.] BRIGHT LINES. 21 



is formed by two very delicate bright lines, similar in size and 

 in distance to the two dark lines D, Fig. 6. Whether the aper 

 ture through which the light of the lamp passes is wide or narrow, 

 if we cover the point of the flame and the lower blue extremity of 

 it, the red line appears less clear, and is more difficult to be dis- 

 tinguished. Hence it appears that this line derives its origin 

 principally from the light of the two extremities of the flame, 

 particularly the inferior one." 1 



But Fraunhofer did not confine himself to flames ; he investi- 

 gated the light produced by electricity : 2 



" The electric light is, in relation to the lines of the spectrum, 

 very different from the light of the sun and of a lamp. In this 

 spectrum we meet with several lines, partly very clear, and 

 one of which, in the green space, seems very brilliant, compared 

 with the other parts of the spectrum. Another line, which is not 

 quite so bright, is in the orange, and appears to be of the same 

 colour as that in the spectrum of the light of a lamp ; but, in 

 measuring its angle of refraction, I find that its light is much more 

 strongly refracted, and nearly as much as the yellow rays of the 

 light of a lamp. Towards the extremity of the spectrum we per- 

 ceive in the red a line of very little brightness ; yet its light has 

 the same refrangibility as that of the clear line of the light of a 

 lamp. In the rest of the spectrum we may still easily distinguish 

 other four lines sufficiently bright." 3 



To sum up Fraunhofer' s first work, we see that he gave us a 

 greatly improved method of observation, and then, as a result 

 of the improved method, the first map of the dark lines in 

 the solar spectrum. Next, by the introduction of the cylindrical 

 lens, he extended our range of observation to the planets 



1 Edin. Phil. Journal, vol. x. p. 39. 2 Ibid. p. 39. 



3 " In order to obtain a continuous electrical light, I brought to within half an 

 inch of each other, two conductors, and I united them by a very fine glass thread. 

 One of the two was connected with an electrical machine, and the other commu- 

 nicated with the ground. In this manner the light appeared to pass continuously 

 along the glass fibre, which consequently formed a fine and brilliant line of 

 light/' Ibid. (note). 



