28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



Smithsonian Institution. 1 However, in Vol. II of our Annals we 

 showed in the second part of the work that the results obtained 

 by this method were harmonious with rougher ones obtained by 

 considering terrestrial meteorological conditions. In the course of 

 that discussion we used the data which were at that time available 

 for determining the transmission through the moist atmosphere of 

 the long-wave radiations such as the earth sends out. Mr. Very 



1 Messrs. Very and Bigelow describe as " the spectro-bolometric method " 

 of determining the solar constant of radiation something quite different, viz. : 

 They take our determination of the form of the solar energy curve outside the 

 atmosphere. From this they determine the wave length of maximum energy, 

 and from it they infer the temperature of the sun, supposing it to be a perfect 

 radiator or " black body." They then determine the intensity of energy which 

 a perfect radiator of the sun's size, and of the temperature which they thus 

 decide upon, would give at the earth's mean distance. This value they regard 

 as the solar constant. 



In this determination they assume : Firstly, that our atmospheric trans- 

 mission coefficients, which at other times they describe as altogether erroneous, 

 do not distort the true form of the sun's energy curve outside the atmosphere; 

 Secondly, that our determinations of the transmission of the optical apparatus 

 (and these we ourselves admit to be determinations of great difficulty, and 

 only moderate accuracy) also do not distort the form of the energy curve; 

 Thirdly, that the position of the maximum of energy determines the proper 

 temperature of the sun; Fourthly, that the total emission of energy of the 

 sun is the same function of its temperature that the total emission of a " black 

 body " is. 



We are far from wishing to discredit the substantial accuracy of our 

 determination of the form of the sun's energy curve outside the atmosphere, 

 but we totally dissent from these authors' application of it. In the first place, 

 the form of the energy curve as determined by us does not agree with the 

 form of the energy curve of a " black body " at any single temperature 

 whatever. In the second place, if the temperature of the sun could be 

 properly inferred from the consideration of the position of maximum energy 

 in its spectrum, even then there would be no reason to suppose that the 

 radiation of the sun bears the same relation to its temperature as the radiation 

 of a " black body " bears to its temperature. Since the sun is not a " black 

 body " of uniform temperature, it may depart widely from the conditions of 

 such a " black body." 



The same method could just as reasonably be applied to the radiation of a 

 mercury vapor lamp. The maximum of energy with such a lamp would be 

 found in the green, as it is in the solar spectrum, and thereby, following Very 

 and Bigelow, one could infer that the temperature of the lamp is of the order 

 of six to seven thousand degrees absolute. Then, following still further our 

 authors, we should assume that the mercury vapor lamp, the sun, and the 

 " black body " at, say, 6,800° would give equal intensities of energy, provided 

 these three sources were of equal angular size. Thus the radiation of all three 

 would be about 3.5 calories per cm. 2 per min. The absurdity of this conclusion 

 is apparent. 



