REPORT OF THE SECRETARY. 



83 



Table 2. — J'alue.'i of the solar constant of radiation from holograjihic studies at 



Washington. 



THE FOR.\I OF THE SOLAR-ENERGY CURVE OUTSIDE THE ATiMOSPHERE AND THE INFERRED 



TE.MPERATURE OF THE SUN. 



Plate VII includes a number of curves which represent on the normal wave-length 

 scale the distribution of energy in the solar spectrum outside the earth's atmosphere. 

 They are computed from prismatic energy curves by aid of the coefficients of instru- 

 mental and atmospheric ab.sorption and the known dispersion of the prism. It will 

 be seen that these recent studies indicate the position of the maximum ordinate at a 

 wave length of about 0.49 /<, or between green and blue of the spectrum, and that 

 there is a fairly close agreement between the different days' work. The principal 

 differences occur in the blue and violet spectrum, and are to some extent caused by 

 the rapid deterioration of the reflecting power of the silvered surfaces in this region, 

 which renders very frequent measurements of instrumental absorption necessary, and 

 even then hardly sufficient. 



Paschen and gthers have established an empirical equation connecting the absolute 

 temperature T with the wave length of maximum energy A„„,^, which is as follows: 



'^max r= CONSTANT. 



The constant in this equation has been determined by Paschen, Lunnner, 

 Pringsheim, and others, to be about 2,900 for an "absolutely black body," t)r jjer- 

 fect radiator, and ranging as low as about 2,600 for bright platinum. Using the 

 former value, we may say that it appears that the radiation of the solar beam outside 

 the earth's atmosphere has its maximum energy at the same wave length as a perfect 

 radiator of the assumed temperature of 5,920° absolute. 



SUMMARY. 



The operations of the year have consisted chiefly: First, in the provision and suc- 

 cessful installation of a horizontal reflecting telescope of 20 inches aperture and 140 



