abbot: solar constant of radiation 



95 



He found transmission coefficients by means of Bouguer's for- 

 mula. He apparent!}' did not investigate the defects of this for- 

 mula as thoroughly as Forbes did. His result for the solar con- 

 stant of radiation is 1.7633 calories per square centimeter per 

 minute. This value, on account of the non-homogeneity of the 

 solar rays, is necessarily too low. 



Quetelet observed with a Robinson actinometer, similar in 

 form to Herschel's, at Brussels, from 1843 to 1853. These ex- 

 periments might well repay a critical examination now, not for 

 their value in determining the absolute measure of the solar 

 constant of radiation, but in connection with the variation of the 

 EA'erage intensity of the solar radiation from year to year as 

 influenced by volcanic eruptions. 



Desains employed a thermopile, and compared the transmissi- 

 bility of the rays of the sun through a water cell at different 

 stations. He found the transmissibility of solar rays through 

 the water cell always increased by a long preliminary course 

 through moist air. This result is essentially the same as that 

 of Forbes, although obtained in a different manner. 



Violle observed at many different stations, including Mont 

 Blanc. His instrument apparently read much too high, as no- 

 ticed by Langley in the report of the Mount Whitney expedi- 

 tion. He used a somewhat complicated empirical formula of 

 extrapolation, as he was fully cognizant of the defect of Bouguer's 

 formula, as indicated by Forbes. He obtained the following 

 values : 



OUTSIDE 

 ATMOSPHERE 



Altitude. . . 

 Barometer. 

 Calories.. . 



2.54 



These values should be reduced about one-fourth to make them 

 comparable with observations made in recent years at high eleva- 

 tions by many observers. In such a case the value outside the 

 atmosphere would become about 1.9 calories. 



Crova made many observations at Mont-Pellier with his alco- 

 hol actinometer standardized against the Tyndall pyrheliometer. 



