120 DR MILLER ON THE METEOROLOGY OF 



the humidity indicated at 3166 feet was rather less than at 2925 feet. This 

 anomaly, though probably accidental, is coincident with the fact, that the average 

 annual fall of rain on Great Gabel exceeds that on Sea Fell by 4*70 inches. 



The results enable us to determine approximately the rate of cooling of the 

 atmosphere by expansion, in ascending on the earth's surface above its general level. 

 This may be computed by two independent classes of observations — either by the 

 observed differences in temperature between the valley and Sea Fell and Gabel, or 

 by the monthly minima recorded by self-registering thermometers at Seathwaite 

 and the mountain stations. 



In 1852, the observed mean difference in temperature between the Vale of 

 Wastdale and the summit of the Pike was 12°7, and, in 1853, 13-5 ; the bien- 

 nial mean is 13°-1 in 2919 feet, showing a fall of 1° in every 222-8 feet of elevation. 

 In the same years, the depression between the valley and the top of the Gabel 

 was ll°-6 and 12° respectively, in 2678 feet; or a mean rate of cooling by dimi- 

 nished pressure equivalent to 1° in 2269 feet, during the day. 



The difference between the absolute monthly minima at Seathwaite and on 

 the Pike was, in 1852, 13°-8, and, in 1853, 12°-7, in 2798 feet,— the mean result 

 indicating a fall of 1° in every 212 feet, at night. A similar comparison with the 

 Gabel gives a depression of 1° in 218-5 feet. The combined results of the day 

 and night observations give a fall of 1 in each 220 feet of elevation. 



The depression in the Dew Point between the valley and Sea Fell Pike was, in 

 1852, 9°-4, and, in 1853, 7 C 8— the combination showing a fall of 1° in 339-4 feet, 

 in a perfectly saturated atmosphere. On the Gabel, the descent in those years 

 was 7 0, 3 and 7 3 respectively, exhibiting a mean variation in the vapour point of 

 1 ' in every 377 feet. The average result is a descent in the dew-point of 1° in 

 3581 feet in height, with a simultaneous fall of 1° in every 224-8 feet in the 

 temperature of the mechanically combined and invisible gases and vapour con- 

 stituting the atmosphere. 



The decrease of temperature in ascending appears to be more sudden dur- 

 ing the night than the day ; and as the mountain thermometers were thickly 

 covered with snow in January, February, March, and December, 1853, the mini- 

 mum temperature recorded in those months and also the annual mean must be 

 considerably higher than would have been indicated had the instruments been 

 freely exposed to the air. It is therefore concluded that the rate of cooling up- 

 wards by expansion is in reality more rapid than is shown by the result elimi- 

 nated from the mean of the day and night observations, or 1° in every 220 feet 

 of ascent. The variation indicated by the night observations alone (l°in 215 feet) 

 is probably nearer the truth. 



The difference in temperature between the valley and the tops of the moun- 

 tains varies greatly, according to the amount of cloud, the presence or absence of 

 mist on the mountains, and the height of the under surface of the Stratus or 



