NEW CLOUD CLASSIFICATIONS. 
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6. Strato-Cumulus (S. Cu.). Large balls or rolls of dark 
cloud which frequently cover the whole sky , especially in winter , 
and give it at times a wave-like appearance. The stratum 
of strato-cumulus is usually not very thick, and blue sky 
often appears in the breaks through it. Between this form 
and the alto-cumulus all possible gradations are found. 
It is distinguished from nimbus by the ball-like or rolled 
form and because it does not tend to bring rain. 
7. Nimbus (N.). Bain clouds. Dense masses of dark , form¬ 
less clouds with ragged edges , from which generally continuous 
rain or snow is falling. Through the breaks in these clouds 
there is almost always seen a high sheet of cirro-stratus or 
alto-stratus. If the mass of nimbus is torn up into small 
patches, or if low fragments of clouds are floating under a 
great nimbus, they may be called fracto-nimbus (“ scud ” of 
the sailors). 
8. Cumulus (Cu.). Piled clouds. Thick clouds whose 
summits are domes with protuberances , but whose bases are flat. 
These clouds appear to form in a diurnal ascensional move¬ 
ment which is almost always apparent. When the cloud is 
opposite the sun the surfaces which are usually seen by the 
observer are more brilliant than the edges of the protuber¬ 
ances. When the illumination comes from the side this 
cloud shows a strong actual shadow. On the sunny side of 
the sky, however, it appears dark with bright edges. The 
true cumulus shows a sharp border above and below. It is 
often torn by strong winds, and the detached parts (fracto- 
cumulus) present continual changes. 
9. Cumulo-Nimbus (Cu. N.). Thunder cloud; shower 
cloud. Heavy masses of clouds rising like mountains , towers , 
or anvils , generally surrounded at the top by a veil or screen of 
fibrous texture (“ false cirrus ”) and below by nimbus-like masses 
of cloud. From their base generally fall local showers of 
rain or snow and sometimes hail or sleet. The upper edges 
are either of compact cumulus-like outline and form mas¬ 
sive summits surrounded by delicate false cirrus, or the 
edges themselves are drawn out into cirrus-like filaments. 
