( 142 ) 



and oxygen in the Earth's atmosphere '). This hypothesis too will, 

 of course, want modification in the light of future results ; but for 

 the present it seems, so far as the visible phenomena are considered, 

 not to clash with any obser\ation or physical law. 



The irregular motion of electrons in the deeper layers of the 

 Sun, where the density is very great, gives rise to the radiation 

 with a continuous spectrum. We shall only take tlds radiation 

 into account. Peculiar radiations, emitted by the more rarefied 

 outer parts of the gaseous body and giving a bright-line spectrum, 

 may perhaps add a perceptible quantity of light to the bulk, but 

 this selective emission, if present, does not play any part in our 

 explanations. So we behold the brilliant core of the Sun through 

 an extensi\'e envelope, consisting of a transparent but selectively 

 absorbing mixture of gases, into which the core gradually spreads. 

 It stands to reason that the a\'erage density of this envelope slowly 

 decreases in the direction from Sun to Earth ; but at right angles to 

 that direction the density must be in some places much more variable. 

 For it is a minimum in the axes of vortices ; and the average 

 direction of the whirl-cores, lying between the Earth and the central 

 parts of the Sun in the surfaces of discontinuity, differs but little 

 from our line of sight. The ra3'S of the Sun thus reach us after 

 having travelled a great distance along lines, making small angles 

 with the levels of slowest density-variation in a lamellar, partly 

 tubular, structure ^). 



Under these circumstances the solar rays will be sensibly incurv^ted 

 on their way through the envelope, especially those suffering ano- 

 malous dispersion. As a rule, beams consisting of the latter kinds 

 of rays will show an increased divergence ; they will reach the 

 Earth with less intensity than the normally refracted light and so 

 will give rise to dark dispersion bands ') in the solar spectrum. And 

 the degree of divergence will not only be different with waves, which 

 in the spectrum are found at different distances from the absorption 

 lines, but it is also clear that the divergence with which various 

 beams of any definite kind of light arrive at the Earth must differ 

 largely according to the dioptrical properties, exhibited along the 



1) A sketch of a solar theory, based on this hypothesis, is to be found in the 

 Revue générale des Sciences, 15, p. 480—495, 30 May 1904. 



2) For considerations which have induced us to hold that a similar structure of 

 the Sun is very probable, 1 refer to former publications: Proc Roy. Acad Amst. 

 IV, p. 162—171; 589—602; V, p. 270—302. 



"') W. H. Julius, Dispersion bands in absorption spectra, Proc. Roy. Acad, at Amst. 

 Vol. VII, p. 134. 



