( 448 ) 
irregular refraction in the sun” l ), viz. : that at a certain level of 
the solar atmosphere (e.g. in the so-called reversing layer, or perhaps 
lower down) the irregular density gradients are comparable in mag¬ 
nitude with the vertical gradient of our terrestrial atmosphere. By a 
simple calculation we showed, that under such circumstances even 
normally refracted waves may be bent into curves whose radii of 
curvature are many times smaller than the radius of the photos¬ 
phere. Light, suffering anomalous dispersion, is curved more strongly 
again. And because the solar atmosphere has a particularly great 
refracting power for R-light and Y-light appertaining to lines of its 
principal constituents, rays of that sort may be quite appreciably 
curved even in much higher levels, though the density gradients 
are smaller there. 
Now, it is evident that not only R-light but also Y-light certainly 
can appear outside the limb of the solar disk by 7 anomalous refraction. 
In the subjoined figures the arcs represent the limit of the 
photosphere. Let regions where a density gradient is supposed to 
Fig. 1. 
exist, be included between a dotted line (where the density be small) 
and a full line (where the density be great). Figures a and b thus 
refer to nearly plane layers with varying density, fig. c to a region 
including a minimum, fig. d to a region including a maximum of 
density. The lines R and V then show us the paths of R-light and 
V-light. 
R-light surely has a better chance to become visible beyond the 
sun’s edge, than V-light, because the general radial gradient, which 
‘) Proc. Roy. Acad. Amsterdam, XII p. 266, 1909. 
