Thus there are three peculiarities attending the forming cirrus of mid-winter (1st of January to 10th of February): long, fibrous, parallel bands in the morning (linear cirrus), gradually coalescing as the day advances, after severe cold; the comoid, curled, or tufted cirrus, in curling bunches, called "_mares'-tails_," and the _transverse_, when the fibers are in bands or threads, which are not parallel, but cross each other at angles, more or less acute. The two former varieties are represented on Figure 5, page 26, indicated by one bird, but the last form is a very prevalent one in our atmosphere. Various names have been given to different forms of _cirro-stratus_. Those represented in Figure 5, page 26, are the "_cymoid_" on the right, the "_mottled_" on the left, below the cirro-cumulus; and the "_linear_" below that. The form known as the "_mackerel sky_" is not represented there. It consists of regular forms, resembling the _waves_ on the surface of the water when the wind blows a gentle breeze. But the _wavy_ form, and of all sizes, is very frequently assumed by cirro-stratus, which is rapidly condensing, and turning to stratus. In the "mackerel sky," strictly so called, the waves are small, parallel, nearly distinct and equi-distant, and resembling the appearance of a school of mackerel, swimming in the same direction, one above another. All _wavy_ forms of cirro-stratus indicate a disposition to increased condensation and rain. When the waves are very large and dense, and cross obliquely, or unite at one end, rain is very certain to fall soon, if the line of progress of the condensation is over the observer, and the clouds are seen in the western or N. W. quarter of the sky. But there are few forms which are not occasionally seen when no rain or snow falls. The intensity of the electric action which produces them may not be sufficient to effect precipitation, or they may be the attendant, attenuated _lateral_ condensation, which frequently "thins out" a considerable distance from the dense, precipitating portions of the storm. If that denser portion is north of us, the probabilities of rain are greater, for there is always a probability that the storm may be of the character which is extended south, by a polar wave. The observer must watch the formation of cirri, and the different forms of cirro-stratus and stratus, and become familiar with their appearance. It is not a difficult task. With the aid of a few general directions he will soon be familiar with them: