NO. 5 SOLAR ECLIPSE I919 ABBOT AND MOORE II 



PYRANOMETRIC OBSERVATIONS OF THE PARTIAL 

 ECLIPSE OF THE SUN OF DECEMBER 3, 1918 



Observations similar to those of May 29, 1919, were carried on by 

 A. F. Moore and L. H. Abbot at the Smithsonian Observatory near 

 Calama, Chile, during the partial solar eclipse of December 3, 1918. 

 The sky radiation was measured on a horizontal surface by the 

 pyranometer during the progress of the eclipse, and the intensity 

 of the solar radiation on a surface normal to the beam was observed 

 with a pair of pyrheliometers mounted equatorially. 



In the accompanying curves the sky radiation is plotted to a scale 

 ten times as large as that for the solar values. It will be seen that 

 the curves are almost identical in shape, showing that throughout the 

 eclipse the light from the sky falHng on a horizontal surface was 

 nearly directly proportional to the intensity of the solar radiation 

 as measured on a surface normal to the beam. This proportionality 

 would probably not hold under other circumstances when the change 

 of solar intensity would be produced by atmospheric changes instead 

 of by causes outside the atmosphere as during the eclipse. The 

 departure from the means of the values before and after the eclipse, 

 to the lowest point, is practically the same for both sun and sky. The 

 drop in the solar radiation is 60 per cent and in the sky radiation 58 

 per cent. (See fig. 3.) 



Following are the values obtained of the sky and solar radiation, 

 at the hour angles and the apparent altitudes of the sun indicated. 



