xni.] LOCUS OF SOLAR ABSORPTION. 163 



them ; and we are apt to forget the scale on which the changes 

 rendered visible to us by our telescopes take place. This is not 

 the case with the different class of phenomena which is 

 revealed to us only during eclipses, when the moon shields 

 the place of observation from ordinary sunlight and, by 

 interposing herself exactly between us and the sun, allows 

 us to inspect the sun's atmosphere with perfect ease. Then 

 new glories are rendered visible which make the moments of 

 the totality as precious to scientific men as they are terrible 

 and awe-inspiring to ordinary beholders. 



1. The Solar Atmosphere. 



Let us, then, attempt to compare the totality of the know- 

 ledge thus acquired with that part of KirchhofFs hypothesis 



FIG. 66. The sun and its atmosphere on KirchhofFs hypothesis. A, luminous 

 haze resting on liquid photosphere ; B, locus of absorption ; c, outer 

 atmosphere. 



which deals with the locus of absorption. The first year's work 

 with the new method showed that the facts did not fit the 

 theory, for the greatest widening of lines was always seen close 

 to the photosphere; as a rule though they were generally 

 thinner than the Fraunhofer lines they were thicker at the 

 bottom than at the top. A diagram, Fig. 66, will show the 

 importance of the last remark. 



If we imagine a slit of a spectroscope normal to the sun 

 cutting the three layers, then the lines should be thickest 

 in the spectrum of B according to Kirchhoffs view. But they 

 were actually thickest at A. 



M 2 



