INSTRUCTIONS TO MARINE METEOROLOGICAL OBSERVERS 75 



Cumulus. — Thick clouds with vertical development; the upper 

 surface is dome shaped and exhibits protuberances, while the base 

 is nearly horizontal (fig. 25). 



When the cloud is opposite to the sun the surfaces normal to the 

 observer are brighter than the edges of the protuberances. When 

 the light comes from the side, the clouds exhibit strong contrasts 

 of light and shade; against the sun, on the other hand, they look 

 dark with a bright edge. 



True cumulus is definitely limited above and below ; its surface 

 often appears hard and clear cut. But one may also observe a 

 cloud resembling ragged cumulus in wdiich the different parts show 

 constant change. This cloud is designated fractocumulus. 



-Cunuiluj- 



(A. J. Hom-y. 



Cumulus, whose base is generally of a grey color, has a uniform 

 structure; that is to say, it is composed of rounded parts right up 

 to its summit with no fibrous structure. Even when highly devel- 

 oped, cumulus can only produce light precipitation. 



Cumulus, when it reaches the altocumulus level, is sometimes 

 capped Avith a light, diffuse, and white veil of more or less lenticular 

 shape, with a delicate striated or flaky structure on its edges; it is 

 generally shaped like a bow, which may cover several domes of 

 the cumulus and finally be pierced by them, 



CmnuJonimhus. — Heavy masses of cloud, with great vertical de- 

 velopment, whose cumuliform summits rise in the form of mountains 

 or towers, the upper parts having a fibrous texture and often spread- 

 ing out in the shape of an anvil (fig. 26). 



The base resembles nimbostratus, and one generally notices virga. 

 This base has often a layer of very low ragged clouds below it. 



5672' 



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