250 



SCIENCE PROGRESS. 



long before formulated, of studying the blood-red streak 

 surrounding the sun without waiting for an eclipse was 

 brought into operation. 



By this method it was quite easy to make observations 

 whenever the sun was shining, perfectly free from any of 

 the difficulties attending the hurry and the worry and the 

 excitement of an eclipse, which lasts only a few seconds. 



B C -D Ef F G 



Fig. i. — Pogson's diagram of the spectra of the sun's surroundings in the 

 Eclipse of 1868. The bright lines seen are shown in the upper part 

 of the diagram ; the chief lines in the solar spectrum, red to the left, 

 blue to the right, are shown in the lower part. 



Fig. 2. — Summation of the observations of the spectrum of the 

 sun's surroundings in the Eclipse of 1868. (1) Solar 

 spectrum showing the position of the chief lines. (2) 

 Rayet's observations of bright lines. (3) Herschel's obser- 

 vations of bright lines. (4) Tennant's. 



Further, as the method consists of throwing an image of 

 the sun, formed by a telescope, on to the slit of a spectro- 

 scope, so that the spectrum of the sun's edge and of the 

 sun's surroundings can be seen at the same time, exact 

 coincidence or want of coincidence between the bright and 

 dark lines can be at once determined. During an eclipse 



