This form has none of the characteristics of the cumulus, and does not appear in the same stratum. It was probably called cumulus because its small masses are distinct, as are those of the ordinary cumulus. It occurs in the same stratum as cirro-stratus, and properly belongs to that modification. I retain the name inasmuch as the cloud is of some practical importance. The cumulo-stratus is seldom seen in our climate, as it is represented in the cut. Stratus condensation _above_, and in connection with cumulus condensation, is not uncommon, but that precise form is rare. This, too, is practically of no consequence, and I shall take no further notice of it. Recapitulating, I give (in a tabular form) the three principal strata and their modifications, located with sufficient accuracy for illustration. The clouds which are found in an upper or lower portion of a stratum are so represented by the location of their names; those which appear at all heights in the stratum, with the names across. The elevation is the average one--although there is no limit to the cirrus above, except the absence of sufficient moisture. It was seen by Guy Lussac, and has been by other aeronauts, at an elevation of five miles, or more, when too delicate to be visible below. +------------------------------------------------+ | | 3 miles. |Cirrus. | | Cirro-cumulus. | | Cirro-stratus. | | | Primary | { Cumulus extending up | stratum. | { in violent showers. | | | | | |Stratus. | |------------------------------------------------| | | 1-1/2 miles. Scud & |N. W. scud. { Cumulus Storm scud. | cumulus |Fair-weather { ordinarily and | stratum. | { its base always. | | | |------------------------------------------------| | | 1/2 mile. Fog |High fog. Storm fog. | stratum. | | | Low fog at the surface of the earth. | | | +------------------------------------------------+ With the assistance of this table of elevations, and a careful observation, the reader can soon become familiar with the forms of clouds and their relative situations. CHAPTER III.