Figure 6. The cirrus by 1 " The cumulus by 3 " The stratus by 2 " The nimbus by 4 " How far these representations correspond with the actual appearance of the different compound forms in England, I can not say. But although they convey a _general_ idea, _they are not sufficiently accurate for practical illustration or observation here_. Indeed Howard himself has omitted from his last edition his plate of the clouds, assigning as a reason, "that the real student will acquire his knowledge in a more solid manner by the observation of nature, without the aid of drawings, and that the _more superficial are liable to be led into error by them_." The collection of forms in the cuts _does not contain some very important ones_, and contains some which are not distinct forms; but they may aid us somewhat in this inquiry, and, therefore, I have copied them. It is well, also, for the reader to have the generally received description before him. But for the purpose of _practical_ illustration hereafter, and greater precision, I shall follow a somewhat different order in describing them, and introduce two forms of _scud_ quite as important, practically, as any other. First, then, commencing at the earth, we have what may be properly termed _fog_, or low fog. This forms, in still clear weather, in the valleys, and over the surface of the rivers and other bodies of water, during the night, and most frequently the latter part of it, and is at its acme at sunrise, or soon after, limiting vision horizontally and perpendicularly, and dissolving away during the forenoon. It is rarely more than from two to four hundred feet in height at its upper surface, and often much less, and is composed of vesicular condensed vapor, sometimes sufficiently dense to fall in mist, and is doubtless in composition substantially what the clouds are in the other strata of the atmosphere, as observed by us, or passed through by aeronauts. I have never seen it carried up to any considerable height into the other strata by any of the supposed ascending currents, to form permanent clouds, and shall have occasion to allude to the fact in another connection. It disappears usually before mid-day, and has, when thus formed, no connection with any clouds which furnish rain. To this Dr. Howard originally gave the name of stratus, and so it is represented upon the cut; but the latter term may be with greater propriety applied to the smooth uniform cloud in the superior strata from which the rain or snow is known to fall, and I shall retain and so apply it.