Cirro-cumulus, on the other hand, does present clearly marked varieties. Cirro-macula is so distinct that it might well be given the name awarded to it by Mr. Ley, while the term “cirro-cumulus” is reserved for the coarser and rounder forms. The hazy, ripple-like structures of Plate 4 and Plate 20 should also have some distinctive appellation, as will be suggested later on when dealing with wave clouds as a whole. It is difficult to find any short way of expressing the various ideas which should be summed up in the name of a cloud. There seems no alternative to the use of additional words, unless it be to follow the example of chemists, and compound appalling names similar to those which terrify the uninitiated who think they would like to read something about, let us say, the coal-tar dyes. If a cloud belongs to the order cirrus, is in a level sheet, and that sheet is composed of interlacing or curling fibres, like those of common cirrus, we can hardly express the facts more briefly than by calling it cirro-stratus communis, or common cirro-stratus. If it consists of cirrus bands fused together, but still showing the banded structure, it is cirro-stratus vittatus. Again, if it is finely speckled, like cirro-macula, it may be described as cirro-stratus maculosus, and if the structure is coarser it may be called cirro-stratus cumulosus. As a general average, cirro-stratus lies somewhat lower in the atmosphere than the detached forms, probably because the conditions which give rise to the latter reach to greater altitudes in patches than it is possible for them to reach in a continuous manner. Vapour becomes rarer with increased height and with diminished temperature, so that it must, on the whole, be less frequently present in cloud-producing quantity as the height increases. At great altitudes it will be seldom that the quantity is great enough to produce a stratiform cloud, though it may well be enough for cirro-macula, or the detached forms of cirrus, like cirrus excelsus.