Mingled with the smoke of London, it produced there the memorable dark day of the 24th of February, 1832, and at various other times has produced others of like character. (See Howard’s Climate of London, vol. iii. pp. 36, 207, 303.) These fogs have been so dense there that every kind of locomotion was dangerous, even with lanterns, at mid-day.
The next in order, ascending, are the storm scud, which float in the north-east or easterly, south-east or southerly wind, before and during storms.
These, as the reader will hereafter see, are, practically, very important forms of cloud condensation—although they have found no place in any practical or scientific description given of the clouds, and are not upon the cuts. They are patches of foggy seeming clouds of all sizes, more or less connected together by thin portions of similar condensation, often passing to the westward, south-westward, north-westward, or northward with great rapidity. Their average height is about half a mile, but they often run much lower. They are usually of an “ashy gray” color. The annexed cut shows one phase of them, from among many taken by daguerreotype. The arrows pointing to the west show the scud distinguished from the smooth partially formed stratus above. This view was taken a few hours prior to the setting in of a heavy S. E. rain storm. It is a northerly view.
Fig. 7.
At about the same height, but in a different state of the atmosphere, float the peculiar fair-weather clouds of the N. W. wind. They usually form in a clear sky, and pass with considerable rapidity to the S. E. Sometimes they are quite large, approaching the cumulus in form, and white, with dark under surfaces, and at others, in the month of November particularly, are entirely dark, and assume the character of squalls and drop flurries of snow; and then resemble the nimbus of Howard. They assume at different times and in different seasons, different shapes like those of the scud, the cumulus, or the stratus.
Fig. 8.
They form and float in the peculiar N. W. current which is usually a fair-weather wind, and are never connected with storms. In mild weather they are usually white, and in cold weather sometimes very black, and at all times differ in color from the ashy gray scud of the storm. This variety is not represented upon the general cuts. The annexed diagram shows one phase of them, but they are readily observable at all seasons of the year, when the N. W. wind is prevailing; differing in appearance according to the season. Let these, as well as the storm scud, be carefully observed and studied by the reader, and let no opportunity to familiarize himself with their appearance be lost. A brief glance at each recurrence of easterly or north-westerly wind will suffice.
