( «74 ) 



the epocli of mid-ei-lipse, we dnuv ;i liorizoiilal line tlirough a i)oint 

 m corresponding to that epoch. The line cnts the descending branch 

 of the curve in /; we make mn^^vil and thus find a point n of 

 the hypothetical radiation curve for constant altitude of the Sun. 

 Acting in a similar Avay for a few more points, we get an idea of 

 the magnitude of the smoothly increasing correction which is to bè 

 applied to the ordinates of the ascending branch. K. Angstrom's 

 measures of the intensity of the radiation for different altitudes of 

 the Sun ') have also been considered in determining the correction. 

 The third column of Table II contains the ordinates of the corrected 

 curve; in the fourth column are given their successive increments 

 which, of course, are the values to be assigned to the absolute terms 



of our equations. I 



' ■ - : 1 



\ Results. 



i Tlie solution of the equations leads to the numbers of Table III; 

 the results-are plotted down in tig. 2 on the plate. Through these 

 points we have drawn a curve satisfying the condition that its 

 urvature should gradually diminish; it shows us the law of variation 

 f the radiating power from the edge toward the center of the solar 

 disk. Putting the ordinate at the center equal to 100 and expressing 

 the other ordinates in the same unit, we get numbers comparable 

 with the results obtained bv other investigators. 

 I The comparison with the spectro-photometric observations by 

 H. C. Vogel ") and with the measurements of total radiation made 

 jvith a radio-micrometer by Wilson ') and with a thermopile b}' 

 Frost ■*), is given in Table IV. We add in Table V the results of a 

 èpectro-bolometric investigation by Very '), as these numbers have 

 been used by Very and by Schuster "} in testing their explanations 

 of the phenomenon. 



: According to Frost's measurements the total radiation appears to 

 diminish from the center toward the limb in about the same pro- 

 portion as the radiation of wave-length 650,ufi, whereas my numbers 

 èhow a decrease very similar to that exhibited by rays of wave- 



1) K. Angstrom, Intensité de la radiation solaire a diflerentes altitudes. RecliercheS 

 faites a Ténérifïe 1895 et 1896. 



2) H. C. Vogel, Ber. d. Berl. Akad. 1877, p. 104. 



8) W. E. Wilson, Proc. Roy. Irish Acad. [3], Vol. 2, p. 299, (1892). 



*) E. B. Frost, Astron. Nachr. 130 (1892), p. 129. 



6) F. W. Very, Astropli. Journ. 16 (1902), p. 73. ; 



6j A. Schuster, Astropli. Journ. 16 (1902), p. 320; 21 (1905), p. 258. 



