206 F. W. Very— On the Solar Constant 



and the heat required to maintain the air column in its gaseous 

 state at the given temperature is 



1020 X 0-238 X 255 = 61904 gram cal. 



To produce this heat during a diurnal period of 12 h , or 720 

 min., 86 gram cal. would have to be communicated to the air 

 column every minute. Besides this, the interchange of heat 

 with surrounding bodies must be considered, and the radiation 

 from such a column would be very great because its surface is 

 large compared with its volume. The solar rays (averaging 

 day and night) probably do not impart more than 1/5 gram 

 cal. per min. to each air column of 1 sq. cm. section. The per- 

 manent heat of the atmosphere is about 400 times this amount 

 and represents the accumulation of nearly 7 hours of sunshine. 

 But this, as we have seen, is much too small, since it supposes 

 that no heat is lost by radiation from the air. If the ther- 

 modynamic reduction to C. G. Min. units had been correctly 

 performed, it would have given 400 gram cal., instead of 4, 

 which indicates that between two and three days of sunshine 

 are necessary to give the accumulated heat of the atmosphere. 

 The table on page 278 exhibits some obscurity in the use of 

 terms. Thus the sum of the pressure differences for the 

 entire atmosphere, that is to say, the atmospheric pressure, is 

 given as approximately 1*45 u gram cal./ cm 2 min." But 

 thermal units are not appropriate for the expression of pres- 

 sures. What has really been done is this : The average 

 atmospheric pressure, in C.G.S. gravitational force units, is 

 1,013,235 dynes per sq. cm. This pressure exerted during 1 

 min. throughout 1 cubic cm. of volume, produces a volume 

 energy of 60,794,100 er^ minutes, equivalent to 1*452 gram 

 cal./ cm 2 min. This may be compared with the volume energy 

 of atmospheric radiation, because, although the solar radiation 

 is never anything else than a continuous flux, the air radiates 

 in a discontinuous, or step-by-step fashion ; and this is as if a 

 definite quantity of radiant energy lingered for a time in a 

 given volume of air, the duration being not that of the 

 radiant transference, which is practically instantaneous, but 

 that of the mechanism of molecular absorption, conduction 

 and reradiation, indefinitely repeated, which requires* time. 

 The volume energy of solar radiation (C. Gr. S.) is the energy 

 received on 1 sq. cm. in 1 sec, distributed through a column of 

 ether 3xl0 10 cm. long. The complex and much retarded 

 process to which the name air radiation is assigned has 

 no such enormous velocity as light, and may be summed, 

 as Bigelow has done, in successive small columns in which it 

 varies progressively, but should then be distinguished from 

 surface radiation in the ordinary sense. When the sum is 



