At Bossekop a fall of snow occurred when the thermometer stood at 10° Fah., and the diameter of the flakes then scarcely exceeded seven hundredths of an inch.

The snow-flake is composed of regular crystals, and its beautiful figures and rich diversity of forms have ever excited the admiration of observers. In solid ice, the crystals are so blended together that their symmetry is lost in the compact mass; but in snow, they are perfectly developed, when the flakes descend through a calm atmosphere. Any agitation of the air, or an increase of moisture or temperature, destroys their deli

cate structure.

If the crystals of snow were solid, they would be transparent, like other crystallized bodies; but they contain air, and to this circumstance is attributed their brilliant whiteness; for the air preventing the ready transmission of light through the snow-flake, the rays are copiously reflected from the assemblage of crystals. The bulk of snow which has just fallen is ten or twelve times greater than that of the water obtained by melting it.

282. Though single crystals always unite at angles of 30°, 60°, or 120°, they nevertheless form, by their different modes of union, several hundred distinct varieties.

Scoresby, a celebrated Arctic navigator, has enumerated six hundred, and delineated ninety-six; and Kaemtz has observed twenty more, not figured by Scoresby.

283. SNOW-CRYSTALS. Although the varieties are so numerous, they are all comprised under five principal classes.

1st. Crystals in the form of thin plates; they are generally very thin, transparent, and of a delicate

How small are they?

Of what is the snow-flake composed?
How is the whiteness of snow caused?

What is said of the bulk of snow?

State the number of varieties of snow-crystals.

In how many classes are they comprised? Describe them.

structure. This class includes many remarkable varieties, which are represented by the first twenty-five figures of the annexed cuts, (15., 16.)

2d. Flakes either possessing a spherical nucleus, or a plane figure, studded with needle-shaped crystals, (figure 26.)

3d. Slender prismatic crystals; usually six-sided, but sometimes having only three sides.

4th. Pyramids with six sides; (figure 27.)

5th. Prismatic crystals, having, perpendicular to their length, both at the extremities and in the middle, thin, six-sided plates; (figures 28., 29. and 30.) The last

two classes are extremely rare, Scoresby having observed the fourth but once, and the fifth only twice, in all his voyages.

Flakes belonging to two consecutive falls of snow, possess different figures; but those which descend during the same storm, are usually alike in this par ticular.

284. NATURAL SNOW-BALLS. Balls of snow are sometimes formed by the action of a high wind upon light snow. Prof. Cleaveland, of Brunswick, in Maine,

observed, on the first of April, 1815, a great number of snow-balls scattered over the fields, varying from one to fifteen inches in diameter. They had evidently been caused by the wind rolling up the snow, as the track of the balls was distinctly visible. In 1830, similar balls were seen by Mr. Sheriff, in East Lothian, scattered over a wide extent; some of the masses being eighteen inches in diameter.

285. But the most remarkable exhibition of this kind was beheld by Mr. Clarke, of Morris county, New Jersey, in January, 1808. A crust having formed upon the snow that had previously fallen, a light snow soon after occurred, covering the glassy surface to the depth of three-quarters of an inch; the sky then suddenly became serene, and a high wind arose. Beneath the force of the gale, small portions of snow would slide along for the distance of ten or twelve inches, when they would begin to revolve, rapidly increasing both in length and diameter. Where the descent of the ground favored their formation, masses rolled up to the size of a barrel, and, as far as the eye could see, the dazzling surface was covered with balls and cylinders of snow; varying in magnitude from ten inches to three feet in diameter. Upon examination they were found to be hollow at each end, almost to the centre, and as round as if they had been so many logs of wood turned in a lathe. The cylinders covered nearly 400 acres, and their number was judged to be nearly 40,000.

286. RED SNOW. In 1819, Capt. Ross beheld snow of a brilliant crimson hue, clothing the sides of the mountains at Baffin's Bay; rising, according to his report, to the height of several hundred feet, and extending to the distance of eight miles.

Snow of this tint is not, however, confined to the Arctic regions. Raymond had previously observed it in the Pyrenees. In 1818, vast masses were spread over the Italian Alps and Apennines, and five years before,

Relate the several accounts of natural snow balls.
What is said of red snow?

the whole range of the last-mentioned chain was covered with rose-colored snow. The same phenomenon was seen by Scoresby, Parry and Franklin, in high northern latitudes, and the navigators of the southern hemisphere have found red snow in great quantities at New Shetland, 62° S. Lat.

287. In snows of great depth, the accounts differ in regard to the thickness of the colored stratum. Ross conjectured, that, in the Arctic mountains, the crimson hue penetrated to the depth of several feet below the surface; while others could not detect its existence beyond one or two inches.

Among the Alps, the red snow is usually discovered in little sheltered hollows, in layers not exceeding two or three inches in thickness: though these are sometimes situated far beneath the general surface of the

snow.

288. GREEN SNOW. When the French meteorologists, Martin and Bravais, traversed a field of snow at Spitzbergen, in 1838, it appeared of a green hue, wherever it was pressed by the foot. The coloring matter seemed to reside just below the surface, which was brilliantly white.

Upon another excursion, the first observer beheld the green particles spread like dust over the snow, which was also tinted green beneath the surface, and upon the sides of the field.

289. CAUSE. These singular hues are produced by the presence of an infinite number of a certain class of microscopic plants, which from their great tenacity of life, are capable, not only of existing at a very low temperature, but even of flourishing with extraordinary vigor.

These minute vegetable forms are composed of globules, which vary in diameter from one-thousandth of an inch to one three-thousandth. Each globule is divided into seven or eight cells, filled with a liquid, in which

What of green snow?

To what cause are those colors attributed?