Many persons are apt to suppose that the clouds are among the most fitful and irregular appearances in the world; fleeting and unstable in their nature, uncertain in their forms, apparently subject to no fixed laws, and obedient neither to times nor seasons. Attentive observers, however, have proved that the beauty and harmony which are everywhere found to prevail in nature when rightly understood, can also be traced, even in the clouds. Although very much still remains to be discovered respecting them, yet it is found that, like all the other natural productions, they admit of being arranged and classified. So obvious was this to persons whose interest it is to observe the weather, that, long before scientific men had studied the subject, country people had noticed the different forms of clouds, and had learned to distinguish them by different names. The first scientific man who made the clouds the object of his particular study, was Luke Howard, who, from an attentive consideration of their forms and appearances, found that they might all be arranged under three simple or primary forms, namely:— 1. The _Cirrus_—so called from its resemblance to a _curled lock of hair_. (Figures, 1, 2; page 77.) 2. The _Cumulus_, from the _heaped_ appearance presented by the convex masses which form this cloud. (Figure 7.) 3. The _Stratus_, from its spreading out horizontally in a continuous layer, and increasing from below. (Figure 10.) These three primary forms are subject to four modifications:— The first is the _Cirro-cumulus_, consisting of small roundish and well-defined masses, in close horizontal arrangement. (Figure 3.) [Picture: Various forms of clouds] The second is the _Cirro-Stratus_, and the masses which compose it are small and rounded, but thinned off towards a part, or towards the whole of their circumference. They are sometimes separate, and sometimes in groups. (Figures 4, 5, 6.) The third is the _Cumulo-Stratus_, which is made up of the cirro-stratus blended with the cumulus. (Figure 8.) The fourth is the _Cumulo-Cirro-Stratus_, or _Nimbus_. This is the true _rain-cloud_, or system of clouds from which rain is falling. (Figure 9.) The term _modification_ applies to the structure or manner in which a given mass of cloud is made up, and not to its precise form or size, which in most clouds varies every instant. Mr. Howard remarks, that it may be at first difficult to distinguish one modification from another, or to trace the narrow limits which sometimes separate the different modifications; but a moderate acquaintance with the subject will soon enable any one to point out the various forms, and to a great extent to judge of the state of the weather by them. In order, therefore, to assist the reader in gaining a certain amount of knowledge on this interesting subject, it may be useful to state more fully the various phenomena of the different forms of clouds already enumerated.