METEOROLOGY. 224 
from the sky. This is not the place for a closer investigation into these 
supposed showers of blood, fruits, sulphur, fishes, toads, stones, &c.; this 
much is certain, however, that in all cases, excepting in that of aerolites 
properly so called, these objects have been elevated by violent aerial 
currents, carried to a considerable distance, and then dropped on the 
abatement of the storm, provided, however, that a descent from the 
atmosphere has actually occurred. 
Of Snow. 
The rain of higher Jatitudes is most frequently presented in the form of 
snow by the freezing of the rain-water in the air. In temperate countries 
this appears to freeze when the temperature is still some degrees above the 
freezing point, while in more southern climes it hardly takes place even 
when the thermometer sinks below 32°F. The shape of the particles of 
snow is exceedingly interesting ; they occur generally as six-sided stars, 
consisting of needles combined at angles of 60° to 120° with each other. 
According to Scoresby, who has instituted the most careful observations on 
this subject, there are five principal forms of snow crystals: Ist. Crystals in 
the form of thin plates; these are most abundant. 2d. Surfaces or spherical 
nuclei with ramifying branches in different planes. 3d. Fine points or 
six-sided prisms. 4th. Six-sided pyramids; occurring but rarely. 5th. 
Prisms, tipped at one or both ends with a thin plate. Some of the most 
interesting figures observed by Scoresby are represented in pl. 23, figs. 4-23. 
The complete and regular crystals of snow appear only during severe cold. 
Should the temperature be several degrees above the freezing point, there 
will be a mixture of snow and rain; the crystals stick together, forming 
flakes of extraordinary size. which, however, are very irregular in shape, 
and soon melt. 
In the torrid zone snow occurs only at great heights above the level of 
the sea, this elevation at the equator amounting to 11,000—12,000 feet. The 
highest mountain peaks, in all countries, if they reach above the snow line, 
will often have snow when rain is falling below them. In Europe the region 
of snow first commences in central Italy, while in Asia and America it 
descends much further south. The isothermal line of 59°F., which passes 
through Florence, may be taken as the commencement of the region where 
snow falls in the lowlands. Ata mean latitude, and at a moderate height 
above the level of the sea, snow generally falls from an overclouded sky, 
when the weather becomes somewhat milder after severe cold, and at a 
temperature higher than the severest winter cold. It is an error, however, to 
suppose that it cannot snow during very severe cold. The latter occurrence 
is not rare in Germany, and Kaemtz observed snow to fall at Halle when the 
thermometer stood at from 5° to 1°F. After snow the weather sometimes 
becomes warmer, sometii.es colder, more frequently the latter, and the 
ensuing cold is severe in proportion to the diminution of temperature during 
the snow-fall itself. 
395 
