in the Air upon the Temperature of the Ground. 261 



that the radiation of the earth is much less refrangible. Put 

 in the absence of a more appropriate determination we may 

 use this for our purpose ; it is probable that for a less hot 

 radiator the absorptive power of the carbonic acid would 

 come out a little greater compared with that of water-vapour, 

 for the absorption-bands of C0 2 are, on the whole, less 

 refrangible than those of H 2 (see pp. 246-248). Using the 

 number 0*03 vol. p. c. for the quantity of carbonic acid in 

 the atmosphere, we find that rays which emanate from the 

 upper part of the air are derived to the extent of 40 p. c. from 

 a layer that constitutes 0*145 part of the atmospbere. This 

 corresponds to a height of about 15,000 metres. Concerning 

 this value we may make the same remark as on the foregoing 

 value. In this case we have neglected the absorption by the 

 small quantities of water-vapour in the higher atmosphere. 

 The temperature-difference of these two layers — the one ab- 

 sorbing, the other radiating — is, according to Glaisher's 

 measurements* (with a little extrapolation), about 42° C. 



For the clouds we get naturally slightly modified numbers. 

 We ought to take the mean height of the clouds that are 

 illuminated by the sun. As such clouds I have chosen the 

 summits of the cumuli that lie at an average height of 

 1855 metres, with a maximum height of 3611 metres and a 

 minimum of 900 metres j-. I have made calculations for 

 mean values of 2000 and 4000 metres (corresponding to dif- 

 ferences of temperature of 30° C. and 20° C. instead of 42° 0. 

 for the earth's surface). 



If we now wish to adjust our formulae (l)'to (3), we have 

 in (1) and (2) to introduce 6 as the mean temperature of the 

 radiating layer and (0 + 42), ((9+30), or (<9 + 20) respectively 

 for the mean temperature of the absorbing layer. In the 

 first case we should use v=l and v = 0*925 respectively, in 

 the second and the third case v = 0"22. 



We then find instead of the formula (3) 



K 



l-rv(l-/3)' 

 another very similar formula 



T4= l + CI <l-/3)' (4) 



- * Joh. Miiller's Lehrhuch d. kosmischen Physik, 5 te -Auft. p. 539 

 (Braunschweig, 1894). 



t According to the measurements of Ekholm and Hagstrom, Bihang 

 till K, Sv % Vet-M. Handlingar, Bd. xii. Afd. 1, No. 10, p. 11 (1886), 



