Ice is water frozen under a very curious and peculiar law.  Hail is the congelation of drops of rain in irregular forms, always sudden,—­by some attributed to electricity and currents of air violently rarefied by it, and by others to rain-drops falling through a cold stratum of air and suddenly congealed.  Snow, the ermine of the earth, is the crystallized moisture of the air, and is in subjection to unchanging laws.

Water contracts as it grows colder, until it falls in temperature to 42 deg..  It then expands till it reaches 32 deg., when it becomes solid, though its density is actually diminished, and its specific gravity is reduced to .929, while that of unfrozen water is 1.000.  Of course it is much lighter, and it floats.  This admirable arrangement prevents our rivers being frozen up and our lakes becoming solid.  Ice thickens because it is porous, and allows the heat of the water to pass up and the cold to descend; but this is happily a slow process, as ice is a bad conductor.  Salt water freezes at the temperature of 7 deg., 25 deg. below freezing-point.  There are many things to be said about ice, whether as glaciers, or Arctic bergs, or, as it is found sometimes, contrary to its general law, at the bottom of rivers and ponds, its geological movements in the transportation of boulders, and as an article of luxury;—­but we are compelled to leave them for the present.

Snow, which, in its crystallization, surpasses the most perfect gems, is invariably found arranged in determinate angles, to wit, 60 deg., and its double, 120 deg., and formed of six-sided prisms.  More than one hundred kinds have been described by Dr. Scoresby and others, and all these are combinations of the six-sided prism.  The uses of snow, from its non-conducting qualities, whether as appreciated by the Esquimaux as a material for huts, or by the agriculturists of our own climate as sheltering the seed, are too well known to require any particular remarks.  Strange as it may appear, the proximate cause of the formation of snow is not yet fully agreed upon by the learned.

The connection between Sound and the atmosphere is an important one.  The air is a conductor of sound, and in some conditions one of the best.  A bell rung in an exhausted receiver gives no sound.  In the Arctic regions ordinary conversations have been distinctly heard for the distance of a mile and a half.

All that we have thus far said in this article bears directly, in some form or other, on another of the great features of Meteorology, one of its great objects, and an unceasing topic,—­namely, Climate.

The term Climate, in its general sense, indicates the changes and condition of the atmosphere, such as we have been considering.  It has something to do with all of them; it is not entirely controlled by any.  Thus, places having the same mean annual temperature often differ materially in climate.  In some (we quote Mrs. Somerville) the winters are mild and the summers cool, whereas in others the extremes of heat and cold prevail.