Fig. 28
There are really four simple cloud formations and three compound formations:
1. The Cirrus Cloud. (Fig. [24].)
The Cirrus cloud is always seen high in the sky and at a great elevation. Its formation is fibrous and it is particularly characterized for its many varieties of shapes. It also has a marked delicacy of substance and it is pure white.
2. The Cumulus Cloud. (Fig. [25].)
The Cumulus cloud is of moderately low elevation. It is a typical cloud of a summer day. It may be recognized by little heaps or bushes rising from a horizontal base. In summer-time we are all familiar with the cumulus clouds rising with the currents of air in huge masses. They form one of the most accurate indications of fair weather when you see them gradually dissolving. Sometimes these clouds become very large, and, while the texture is generally of a woolly white, naturally, when they assume such large sizes, they gradually change in color to a darkish tint.
3. The Stratus Cloud. (Fig. [26].)
This is the opposite of the Cirrus cloud, because it hangs the lowest of all, in gray masses or sheets, with a poorly-defined outline.
4. The Nimbus Cloud. (Fig. [27].)
Any cloud can be classed as a nimbus cloud from which rain or snow is falling.