[Picture: The Cirrus, or curl-cloud] The Cirrus occurs in very great variety, and in some states of the air is constantly changing. It is the first cloud that appears in serene weather, and is always at a great height. The first traces of the cirrus are some fine whitish threads, delicately-pencilled on a clear blue sky; and as they increase in length others frequently appear at the sides, until numerous branches are formed, extending in all directions. Sometimes these lines cross each other and form a sort of delicate net-work. In dry weather the cirrus is sharp, defined, and fibrous in texture, the lines vanishing off in fine points. When the air is damp this cloud may be seen in the intervals of rain, but is not well defined, and the lines are much less fibrous. Such cirri as these often grow into other varieties of cloud, and are frequently followed by rain. The cirrus may last a few minutes only, or continue for hours. Its duration is shortest when near other clouds. Although it appears to be stationary, it has some connexion with the motions of the atmosphere; for whenever, in fair weather, light variable breezes prevail, cirri are generally present. When they appear in wet weather, they quickly pass into the cirro-stratus. According to Dalton, these clouds are from three to five miles above the earth’s surface. When viewed from the summits of the highest mountains they appear as distant as from the plains. Another proof of their great height is, their continuing to be tinged by the sun’s rays in the evening twilight with the most vivid colours, while the denser clouds are in the deepest shade. The cirrus appears to be stationary; but, on comparison with a fixed object, it will sometimes be found to make considerable progress. THE CUMULUS, OR STACKEN-CLOUD. “And now the mists from earth are clouds in heaven: Clouds, slowly castellating in a calm Sublimer than a storm; while brighter breathes O’er the whole firmament the breadth of blue, Because of that excessive purity Of all those hanging snow-white palaces, A gentle contrast, but with power divine.” The Cumulus is a day cloud; it usually has a dense, compact appearance, and moves with the wind. In the latter part of a clear morning a small irregular spot appears suddenly at a moderate elevation. This is the nucleus or commencement of the cloud, the upper part of which soon becomes rounded and well defined, while the lower forms an irregular straight line. The cloud evidently increases in size on the convex surface, one heap succeeding another, until a pile of cloud is raised or _stacked_ into one large and elevated mass, or _stacken-cloud_, of stupendous magnitude and beauty, disclosing mountain summits tipped with the brightest silver; the whole floating along with its point to the sky, while the lower surface continues parallel with the horizon. [Picture: The Cumulus, or stacken-cloud]