February [3, [919] 



NATURE 



475 



Doled irface, and travel horizontally thunderstorms. Those in the photographs 



. the air being turbulent jusl under- | thunderstorms which reached 20,000 Ft. 

 nc ath them. In winter 

 h< prevenl local inland 



d 

 veloping, as thi . 

 back the radiation from 

 the mii ' 



In many cases in « inter 

 iccurate 



and thi< km ss of th<' 



could bi made on 



isumplion thai ihej 



horizontally with- 



i form. This 



foi some cloud- 



uiih their lower 



pra< ticall) on the 



ground, when the aii 



above them is in a stable 



condition. On summer 



la\ 5 o\ ei the land th< 



tend ••>• assume the 



form of cumulus, bul 



their heigh! and 1 h 



1 Id from 



temperature a n d 

 humidih al di 

 heights.' 



1 and .' show 

 cumulo - nimbus 

 over the sea which had 

 grown up through a 

 sheel bi 00 ft. 



I! - 'In" wen r.c.* -Rounded top of a cumulo-nimbus cloud from which a shower is falling. Snowshowi 



Cumulus Clouds from high cloud in background. S a.m., September 19, 1918. 



resulted in 

 lightning 





Fig. I ;e lowering cumuli. 6 p.m., 



j ft. upwards, and some of them grew up through 

 cloud-sheet and finally developed into showers 01 



NO. 2572, VOL. I02] 



The ' 

 Figs. 



being seen after dark-. 

 The conditions were un- 

 stable, the temperature 

 bi in- 6o° at the sur- 

 faci . 49 at 2000 ft. , 

 and 6° at 13,000 fl . ; 

 the adiabatic for satu- 

 rated air i- 3^° F. per 



ft. I he lapse-rati 



jusl above the cloud- 

 shei 1 hi 8000 ft. was 

 stable enough to allow 

 it to pet -isi for a few 

 hours, except where it 

 was broken through 

 from b e 1 o w. The 

 cumulo-nimbus on the 

 lift of Fig. 1 had a 

 ven strange form, and 

 had grown larger when 

 Fig. 2 was taken ten 

 minutes latei . I li 1 



1 louds m o v e il from 

 W.N.W., bul the form 

 of the false cirrus cm 

 the top of tin- cumulo- 

 nimbus gives evidence 

 of the existem - of a 

 south - westerly current 

 at 20,000 ft., « hich pos- 

 sibly caused a slight 

 inversion, and was re- 

 sponsible for the flat top 

 of th< distant cumulo- 

 nimbus on the right. 

 false cirrus," of which an example is seen in 

 1 and 2, consists of thin snow, which is- 



