F. W. Very — Note on Atmospheric Radiation. 537 



energy through the atmosphere by the modified radiant 

 process, outlined here, and a pure radiation. The sudden 

 increase in the constant second differential of Q at the isother- 

 mal level, strongly suggests an accession of immediate radiation 

 to space above this point, and a progressive diminution of the 

 indirect radiant process from thence outward, together with a 

 cessation of aqueous condensation which supplies considerable 

 heat to the lower layers, while further loss of temperature is 

 only permitted through the gradual removal of absorbent sub- 

 stances which prevent the passage of radiation of great wave- 

 length, characteristic of still lower temperatures. 



The methods employed by Bigelow still retain something of 

 empiricism. Wherever a temperature gradient less than that 

 of the adiabatic rate prevails in the atmosphere, some heat 

 must have been supplied by radiation, or by condensation of 

 aqueous vapor, or in other ways ; and this extraneous addition 

 is not taken into account by the formula which connects the 

 density with temperature and pressure. It is known from 

 laboratory experiments that the specific heat of air at constant 

 pressure is very nearly constant between — 39° C. and + 200° C. 

 Wherever the values of Cp computed by Bigelow's formula 

 depart from the true value given by laboratory experiment, 

 the deviation of the fictitious or apparent Cp denotes that only 

 a part of the thermal variation with the altitude is due to 

 simple mechanical transportation and expansion of masses of 

 air. The deviation becomes progressively greater in the upper 

 air where production of heat by absorption of solar radiation 

 is large. From the intimate relation between Cp and R, the 

 gas factor, a corresponding variation is produced in the fictitious 

 value of R. Similarly, if the computed value of the air radia- 

 tion is larger than that of AQ in the lower layers of air, this 

 must mean that the data employed include other phenomena 

 besides those of radiation. Although the upper air is more 

 transmissive than the lower air for radiations of wave length 

 less than 15/x, the final limit to further decrease of temperature 

 by atmospheric radiation to free space appears to result from 

 the virtual opacity of the air to longer waves than these, 

 coupled with the fact that a temperature has been reached at 

 which these long- waved radiations constitute the greater part 

 of the radiant output. This limit is only extended by the very 

 gradual removal of the last traces of absorbent at still 

 greater altitudes. These remarks are not intended as a criti- 

 cism of the methods, for it is difficult to see how any others 

 can be used, but are made to point out the limitations of an 

 analysis which is obliged to deal with data covering a variety of 

 simultaneous processes in unknown proportions, and in the 

 endeavor to elucidate the meaning of the results. 



