12 



NATURE 



{May 2, 1889 



with so little satisfaction to the already burdened agri- 

 culturist, can hardly fail to prove of interest to the 

 zoological student of farm pests. 



Allen Harker. 

 Royal Agricultural College, Cirencester, April 10. 



RAIN CLOUDS ON LAKE TI TIC AC A. 



THE cloud system here, 12,500 feet above sea-level, is 

 so beautiful, and seems to throw so much light on 

 the formation of one particular type of shower, that I 

 venture to send diagrammatic sketches of two excellent 

 specimens of cloud-building over rain. 



I have never seen cumuloform clouds so perfectly 

 developed as on this lake. Whether the height above the 

 dust and haze of lower levels makes the blue sky darker 

 than usual, or whether the temperature is such that the 

 cumulus is composed of snow-flakes instead of water- 

 drops, the contrast between the sky and cloud is much 

 greater than usual. 



The sketches were taken on a showery day, and the 

 clouds were visible simultaneously in different directions. 

 The type of shower is not unknown at home, but there 

 much complication arises from the almost constant 

 existence of cyclonic cloud systems. 



Certain features are common to both pictures. Nearest 

 the earth, appears a more or less conical-shaped space r. 



Fig. I. — /', blue sky ; c, flat-topped mass of dark cloui, rounded components ; r, rain ; iv, white cloud, tending to flatter, out and to cirrify. 



Fig. 2. — b, blue sky ; c, dark cumuloform cloud, flat-topped at edges; d, dark belt ; r, rain ; 7t', white cloud, tending to fl itten and to cirrify. 



of uniform inky blackness, where rain is falling. Above, 

 and stretching laterally some distance beyond the rain, is 

 a belt of dark cloud, c, curiously flattened at the top ; but 

 the outhnes are always rounded, and there is no trace of 

 linear or hairy structure. In Fig. 2 a mountainous rocky 

 cumulus rises above the flat dark mass c ; and as the rain 

 could be seen falling, I have indicated that appearance in 

 the sketch. 



In both, a white cloud, w, of remarkable shape and 

 structure, rises above the dark mass c. Sometimes, as in 

 Fig. I, this cloud is nearly uniform in structure, but exhibits 

 a tendency towards hairy structure at the edges. Other 

 times, as in Fig, 2, the white clood iv shows traces of 



cumuloform structure of a very peculiar type. Instead of 

 round, rocky lumps, the white cloud is composed of long, 

 straight, fingery masses of cumulus, with a tendency to 

 fibrous or hairy structure, and radiating slighUy outwards 

 from the base, like the head of a cauliflower. I have en- 

 deavoured to suggest this appearance by the straight 

 hnes, drawn through w, in Fig. 2 ; for the real structure 

 defies delineation with pen or pencil. 



In all cases, the top of iv is more or less flat, and the 

 whole diffuses outwards, sideways, or edgeways, rather 

 than upwards. As the shower breaks up, w seems tb be 

 left as a middle-level layer of strato-cirrus. 



The whole shower is surrounded by blue sky, there is 



