1903.] Observations obtained by the Use of Kites. 15 



air of different heights derived from all the Oman ascents are as 

 follows : 



Height of column. Temperature gradient. 



Metres. Per 100 metres. 



500 0-56 



1000 0-56 



1500 0-52 



2000 0-50 



2500 0-48 



3000 0-46 



3500 0-43 



It must be remembered that a moderately strong wind was required 

 for the higher ascents, and they therefore refer to a more or less special 

 type of weather. The gradients for the higher columns are accordingly 

 not so generally applicable as those for the lower columns. 



The results are compared with temperature gradients observed else- 

 where as given in Hann's " Meteorologie," with the theoretical 

 temperature gradient in dry air (1 C. per 100 metres), and with that 

 for saturated air having an initial temperature 12 C. The last differs 

 but little from 0'53 C. per 100 metres for all ranges up to 2000 metres 

 and then increases. The average Crinan gradient is almost identical 

 with this and with the conventional correction in use in this country 

 for the reduction of temperatures to a common level, viz., 1 F. per 

 300 feet. 



The last part of the paper is devoted to considering the differences 

 between the temperatures as observed in the free air at the same height 

 as the summit of Ben Nevis and those read on the mountain itself. 

 The differences are always in favour of the free air, which is shown to 

 be on the average 2*6 warmer than the mountain summit. Various 

 circumstances are adduced to support the result, and an explanation is 

 sought in the suggestion that the air flowing from the sea over the 

 mountain would be mechanically raised and practically subject to the 

 adiabatic gradient which is not reached in the free air. The considera- 

 tion of the relative heights of clouds as observed on the hill sides and 

 over the sea is adduced in corroboration. 



