1465 
to the places defined in the fifth column. Our results are thus made 
more easily comparable with those obtained by other observers. 
It is not surprising to find the shape of our distribution-curve 
sensibly different from the shape of any of the curves that repre- 
sent Voarr’s speetrophotometrie measurements. Indeed, the latter 
show the distributions characteristic of special groups of rays, each 
covering a narrow part of the spectrum; they are germane, but 
yet vary considerably with the wave-length. The combined effect of 
all waves (invisible ones included), that are absorbed by our ther- 
mopile, must give a distribution-curve of another type, less simple 
than that to which Voeer’s curves for nearly monochromatic light 
belong. 
Summary. 
During the annular eclipse of the sun-on April 17 1912 the 
variation of the total radiation has been observed near Maastricht 
under exceptionally favourable sky-conditions, with two mutually 
independent sets of apparatus. 
One set, comprising a bolometer and a short-period recording 
galvanometer, served the purpose of finding as accurately as possi- 
ble the proportion of the minimum to the maximum radiation. 
The ratio was found to be nearly ’/,,,,. On this result we based 
an estimate of the total amount of energy radiated and seattered by 
the entire solar atmosphere; we thus obtained a very small fraction 
of the solar output (about */,,,,). 
It is impossible, therefore, to ascribe the fall of the sun’s bright- 
ness from the centre toward the limb of the disk to absorption or 
scattering of the light by an atmosphere, enveloping a body that 
otherwise would appear uniformly luminous. The cloud-theory of the 
photosphere is not borne out by the facts. 
With the other set of apparatus, consisting of a thermopile and 
accessories, we obtained a sufficient number of reliable readings for 
constructing the whole radiation-curve, from the first until the 
fourth contact, with a fair degree of exactness. Besides confirming 
the value of the minimum as found with the bolometer, this curve 
procured the data necessary for onee more determining the rate of 
decrease of the radiating power from the centre to the limb of the 
solar disk. 
