in the Air upon the Temperature of the Ground. 249 



vapour, the last two to that of carbonic acid. It should be 

 emphasized that Langley has applied the greatest diligence 

 in the measurement of the intensity of the moon's radiation 

 at angles between 36° and 38°, where this radiation possesses 

 its maximum intensity. It may, therefore, be assumed that the 

 calculated absorption-coefficients for this part of the spectrum 

 are the most exact. This is of great importance for the fol- 

 lowing calculations, for the radiation from the earth * has by 

 far the greatest intensity (about two thirds, cf. p. 250) in this 

 portion of the spectrum. 



II. The Total Absorption by Atmospheres of Varying 

 Composition. 



As we have now determined, in the manner described, the 

 values of the absorption-coefficients for all kinds of rays, it 

 will with the help of Langley's figures | be possible to cal- 

 culate the fraction of the heat from a body at 15° 0. (the earth) 

 which is absorbed by an atmosphere that contains specified 

 quantities of carbonic acid and water- vapour. To begin with, 

 we will execute this calculation with the values K=l and 

 W = 0*3. We take that kind of ray for which the best deter- 

 minations have been made by Langley, and this lies in the midst 

 of the most important part of ths radiation (37°). For this 

 pencil of rays we find the intensity of radiation at K=l and 

 W = 0*3 equal to 62*9; and with the help of the absorption- 

 coefficients we calculate the intensity for K = and W=0, 

 and find it equal to 105. Then we use Langley's experiments 

 on the spectral distribution of the radiation from a body of 

 15° C, and calculate the intensity for all other angles of devia- 

 tion. These intensities are given under the heading M. After 

 this we have to calculate the values for K = l and W = 0'3. 

 For the angle 37° we know it to be 62*9. For any other 

 angle we could take the values A from Table II. if the moon 

 were a body of 15° C. But a calculation of the figures of 

 Very J shows that the full moon has a higher temperature, 

 about 100° 0. Now the spectral distribution is nearly, but 

 not quite, the same for the heat from a body of 15° C. and 

 for that from one of 100° C. With the help of Langley's 

 figures it is, however, easy to reduce the intensities for the 

 hot body at 100° (the moon) to be valid for a body at 15° 



* After having been sifted through an atmosphere of K = l*l and 

 W=0 3. 



t ' Temperature of the Moon/ plate 5. 



j "The Distribution of the Moon's Heat," Utrecht Society of Arts and 

 Sc. The Hague, 1891. 



