Cumulus clouds form at a low altitude, but they frequently tower upward to great heights. It should be noticed that in these clouds the fine weather form is of soft, smooth outline, and has a quiet appearance. _Stratus Clouds_ may be divided into four varieties as follows: 1. _Fog_, so well known as not to need description. It is, in fact, a Stratus cloud resting on the earth’s surface. 2. _Stratus_, a cloud sheet which covers the whole sky at a moderate elevation. Here and there the cloud is thin, and under surfaces appear as parallel lines all round the horizon. This is the characteristic cloud of anti-cyclonic, or dry, fine weather conditions. It may continue to cover the sky for several days in succession. 3. _High Stratus_, including all the varying forms of Cirro-cumulus from the mackerel skies to the Cirro-macula of Clement Ley. Many beautiful varieties of this cloud of minute cumuliform appearance are caused by the changes taking place in the atmosphere. We notice waves, wavelets, stipplings, and flecks. To it are due the coronas sometimes seen round the sun, as also iridescent clouds occasionally noticed in the same vicinity. The wave-like appearance of the clouds is due to the passage of a more rapidly moving air current over a slower one, or of a wave current crossing a motionless portion of the air. When two air currents pass over one another at an angle, the particles of clouds tend to fall into different shapes, hence our mackerel skies. But this cloud, although beautiful, is essentially one of warning, more especially when the flecks are of a thin, scaly appearance (resembling the scales of certain fishes so closely that I have called it the scale cloud). Sometimes these detached flecks appear in lines, and very striking is the effect produced. 4. _Cirrus._--The highest form of cloud and the most important as a factor in the science of weather forecasting. Cirrus, ordinarily, appears as wisps and feather pieces scattered over the sky, and its significance is then of no import. When, however, this cloud takes the form of lines parallel to the horizon, or of lines appearing to radiate as wheel-spokes from any one part of the horizon, it should be carefully noted as indicative of approaching weather. Its movement and propagating transition should be observed. This cloud is composed of ice-dust or crystals. When a cyclonic disturbance is about to pass over an observer, Cirrus generally appears first in parallel lines, or at a radiant point; the threads gradually increase and interlace until a complete sheet of Cirro-stratus covers the sky, causing a halo. The cloud further thickens, the halo disappears, all becomes overcast, and rain comes on. The cloud is now known as Nimbus, and after it has endured some time, the wind shifts, the Nimbus clears off, and it is succeeded by a polar west wind.