78 
(It is noteworthy that w also receives radiation from e originating 
from regions e’ and e’’ in the neighbourhood of the radius vector 
je, which radiation has finally assumed the direction ew through 
diffusion and irregular refraction). 
Let us now consider the energy curves of the radiations coming 
from those different regions, as functions of the wavelength. All of 
them will probably have the character of the curve of radiation of 
the absolutely black body: slow increase of the energy from the 
infra-red to a maximum, and then a comparatively rapid decrease 
on the violet side of the maximum. The loci of the maxima of the 
different curves are determined not only by the temperature of the 
corresponding radiations, but also by the relative importance of 
diffusion aud refractional scattering. Since the light of shorter wave- 
lengths is much more greatly weakened by diffusion than that of 
longer wavelength, the maximum will be displaced by the diffusion 
towards the side of the longer wavelengths; the irregular refraction, 
on the other hand, does not displace the maximum, because it is 
almost independent of the wavelength. For the curves belonging to 
the radiation originating from deeper layers, the maximum would 
lie more to the violet than for the curves belonging to the outer 
layers, if the temperature were the only factor; more to the red, 
however, if exclusively the diffusion were efficient. The height of 
the maximum is determined by the temperature of the radiation, 
the density at the places of emission, and the weakening which the 
radiation has undergone by diffusion, irregular refraction, and ab- 
sorption. 
We may therefore conclude that from the centre of the sun’s 
dise a quantity of energy is emitted in the direction w of which the 
energy curve, proceeding from the infra-red towards smaller wave- 
lengths increases, at first slowly, then more rapidly to a flat maxi- 
mum, and then runs very steeply down to the violet (fig. 3 1). 
Not far from the limb of the disc, e.g. at c (fig. 2), we shall 
receive light from a longer path through the gases (ek > bj), but it 
will come from less deep layers. Hence at the limb radiation is 
received from f only from the regions round 47 lying more out- 
wardly. The quantity of energy that w receives from the limb of 
the dise is therefore for all colours smaller than that which w receives 
from the centre. Hence the energy curve of the limb of the sun 
will as a whole lie lower than that of the centre. // the diminution 
of energy were the same for all the colours, the composition of the 
light at the limb would be represented by a curve which had the 
same shape as that of the centre (fig. 3 II). Now it is directly to be 
