( 6?fi ) 



limh would doubtless have been found quicker for all wave-lengths, 

 and, very probably, the distribution for the region 650;j,u would have 

 proved to agree better witli my results than with the uncorrected 

 values of Frost. 



Wn,soN's measurements seem to iiave been influenced by other 

 causes of error still, liesides atmospheric scattering, as his numb.ers 

 are greater than those obtained by Frost, and harmonize not as well 

 as the latter with the spectro-photometric series. 



The observations of Very have given considerably greater ratios 

 in the marginal regions than those of Vogel. Mr. Very himself points 

 out the dilference, and remarks that the bolometer has an advantage 

 over the eye in the red where the heat is great ; but I may suggest, 

 on the other hand, that instrumental errors (reflection or scattering 

 of light by prisms, lenses, tubes, etc.^ are easier discovered and 

 corrected in spectro-photometric than in spectro-bolometric work. 



It seems to me that observing an eclipse-cur\e by means of a 

 ver^' simple but sensitive actinometer, without lenses or mirrors, 

 must yield results concerning the radiation of different pai'ts of the 

 solar disk Avhich deserve more confidence than the values hitherto 

 obtained in other ways. I wish to lay stress upon the advantages of 

 our method, rather than on the reliability of the numbers secured 

 at Burgos under not very favourable circumstances. In a clear sky 

 the shape of the eclipse curve will easily be found with very great 

 accuracy. 



The same method will also be applicable with radiations covering 

 limited parts of the spectrum, if we only put suitable ray-filters 

 before the opening of one of the diaphragms in the actinometer. It 

 may even be possible, in a future eclipse, to use an arrangement 

 which brings several ray-filters by turns before the opening ; thus, 

 when disposing of a quick galvanometer, one would be able to 

 simultaneously determine, with one actinometer, the eclipse curves 

 for rays belonging to five or more regions of the spectrum, and the 

 results would be independent of selective atmospheric scattering. 



Remarks on the hypotJieses used for explaining the distribution of 

 the radiating power on the solar disk. 



The diminution of the intensity of radiatioji toward the limb is 

 almost generally ascribed to absorption of the rays by the solar 

 atmosphere '), and it is supposed that, in absence of that atmosphere, 



Ï) J. ScHEiNER goes as far as to say: "Eine andere Doutung des Lichtabfalls ist 

 -niclit zulassig." (Slralilung und Temperatur dor Sonne, p. 40). 



