314 G. A. Young on the Solar Corona. 



especially as the sky was full of haze and light cirrus clouds at 

 all, or nearly all, the stations of observation. 



It is certainly difficult to say that such might not have been 

 the case to some extent, for the hydrogen lines were seen at an 

 elevation of 4' to 5', far above any possible hydrogen, and 

 faintly even on the disc of the moon itself— evidently by just 

 such an atmospheric reflection. 



There is, however, an important difference between the behav- 

 ior of the hydrogen lines, and that of 1474 At the edge of 

 the chromosphere there was a sudden and very great falling off 

 in the brightness of the former, while no such boundary was 

 observed for the latter ; the line grew regularly and continu- 

 ously more faint as the distance from the sun increased, until it 

 srniply faded out, no abrupt alteration of its brilliancy being 

 anywhere noticed. (I now speak of my own observations; but 

 so far as I have learned, the experience of others was the 



In 1869 the difference between the hydrogen lines and 1474 

 was still more marked. The former could hardly be traced at 

 all beyond the actual limit of the chromosphere, the air being 

 so clear that there was very little atmospheric effect. 



But there is another way of approaching the subject. The 

 spectroscopes used by our party at Jerez were of two dmerent 

 classes, and by a combination of their results we may obtain an 

 indication of considerable value. ^ ,, 



In the instruments employed by Prof. Winlock and myself, 

 and I presume by the greater number of the eclipse obsemrs, 

 the spectroscope is attached to the eye-end of a telescope wfiose 

 object-glass throws upon the slit a distinct image of the boay 

 to be examined. Such an instrument may be called an analyz- 

 ing spectroscope, since it deals with ele- 

 mentary portions of the luminous area under 

 investigation. Thus, if the figure represent 

 the image of the corona, chromosphere and 

 moon formed by the object-glass of the tele- 

 scope, then if the slit be placed as at S, the 

 spectrum seen will be produced solely by 

 light from those elements of the luminous 

 area whose foci fall within its jaws. The spec- 

 trum will be divided longitudinally into two r. g 

 portions, of which the one derived from the ^PP^^ portion oi 

 will show only the lines due to the leucosphere, while the o 

 will exhibit the chromosphere lines plus those of the leucosp^re. 



(Of course it must be remembered that while the ^W°°^^. 

 does not extend above the limit of the chromosphere, the co _^ 

 nal matter does reach down to the surface of the sun, an 

 the chromosphere is mingled with the hydrogen ; indeed, ex y 



