As a general rule, it is stated that the natural region of clouds is a stratum of the atmosphere lying between the level of the first thousand feet, and that of one removed about ten thousand feet above it. Of course it is not supposed but that clouds are occasionally found on both sides of the bounds here assigned to them; the mist occupies the lowest valleys, while, on the other hand, long after the aëronaut has attained the height of ten thousand feet, some faint indications of clouds may still be seen partially obscuring the dark blue vault above him. As he continues to ascend, the blue of the sky increases in intensity; and should a layer of clouds shut out all view of the earth, “above and all around him extends a firmament dyed in purple of the intensest hue; and from the apparent regularity of the horizontal plane on which it rests, bearing the resemblance of a large inverted bowl of dark blue porcelain standing upon a rich Mosaic floor or tesselated pavement. Ascending still higher, the colour of the sky, especially about the zenith, is to be compared with the deepest shade of Prussian blue.” [Picture: Various forms of hail-stones] CHAPTER IV. ON HAIL—THE HAIL-STORMS OF FRANCE—DISASTROUS EFFECTS OF HAIL—THE HAIL-STORMS OF SOUTH AMERICA—THEIR SURPRISING EFFECTS—ORIGIN AND NATURE OF HAIL—PERIODICAL FALLS OF HAIL—HAIL CLOUDS—HAILSTONES—THEIR VARIOUS FORMS—EXTRAORDINARY SIZE OF HAILSTONES. As hail seems to be nothing more than frozen rain, it is necessary to collect a few particulars respecting it in this place.