93 
Unfortunately, however, a fatal error has slipped in. For to 2 = 0.6 
does not correspond /, = 350, but — (interpolating graphically) — 
1, = 506, which yields 7’—= 6600° instead of 8700°, so that agreement 
is out of the question. 
A serious objection to the whole method seems perfectly obvious 
to me, namely this: 
The assumption that all kinds of light come to us from one 
photospheric surface, in other words that light of various wavelengths 
should come from the same depth of the sun, appears more and 
more untenable in the light of recent researches (see e.g. the thesis 
for the doctorate of J. SpijkerBoeErR “Verstrooiing van licht en intensi- 
teitsverdeeling over de zonneschijf” (1917) (Dispersion of light and 
Distribution of Intensity over the Sun’s Disc)). If, however, in reality 
light of different wavelengths originates from different parts of the 
sun, it becomes very questionable whether we shall be allowed to 
apply PrANCK’s formula, as we saw Derrant do. For this would mean 
that we supposed every kind of light to have, as it were, a_kind 
of “photosphere of its own”, which radiates as a black body, the 
photosphere for the greater wavelengths lying deeper than that for the 
smaller. It might then be expected that the temperature determined 
with PANck’s formula, becomes a function of 2, i.e. 7’ would be 
the greater as 4 increases. 
In this latter remark we have a means to investigate whether 
the hypothesis that the photospheres overlap each other like scales 
ean find a semblance of justification. 
By graphical interpolation from the values of table II I construed 
table III: 
TABLE III. 
A h A h A h FA h 
0.40 709 0.70 342 1.00 134 1.60° (|) 46 
0.45 791 0.75 284 1.10 104 1.70 39 
0.50 114 0.80 | 239 old Si 1.80 32 
0.55 604 0.85 201 1.30 74 1.90 | 25 
0.60 506 0.90 174 1.40 64 S00 ok 19 
0.65 418 0.95 153 1.50 55 | 
| 
As we do not know the unity in which /, is expressed, we 
require, as was already remarked before, always two values of DP 
(a, and a,) to find 7. 
