CHAP. 1. 3. OF CLOUDS. 9 



SECTION III. 



Of the Cumulus or StacJeencloud. PI. I. Fig. 3. 

 CVMVLVS. Def. NVBES CVMVLATA DENSA SVRSVM 



CRESCENS. 



THE cumulus is a convex aggregate of watery 

 particles increasing upwards from a horizontal 

 base. It is commonly of a dense structure, 

 formed in the lower atmosphere, and moving 

 along in the current of wind which is next to 

 the earth. Its first appearance is generally a 

 small irregular spot, which becomes the nucleus 

 on which it forms. This increases in size, pre- 

 serves a flat horizontal base, and assumes more 

 or less of a conical figure. Cumuli vary in 

 shape and dimensions, according to peculiarities 

 in the operation of the causes which produce 

 them. Sometimes they are pretty well defined 

 hemispherical masses; at others, they rise into 

 mountains, ranged in one plane, their silvery 

 summits presenting a beautiful appearance. In 

 particular kinds of weather, I have seen cumuli 

 of a sort of tuberculated structure. Before rain, 

 they increase very rapidly, descend lower in the 



