pass in flocks, is said to resemble the notes of a violin. The rich provision of down with which Arctic birds are furnished, as in the eider-duck, is well known; the beauty of the furs in the land animals, also makes them valuable in commerce.

The migration of birds, though taking place on the change from heat to cold, or vice versa, is, perhaps, not caused so much by this change itself, as by the diminution of food under certain temperatures. Thus, while in the Arctic summer many birds find in the forests and morasses a sufficient supply, yet when the early winter begins to bind up the lakes and shores, they are deprived of sustenance, and obliged to come to more temperate regions to seek it. To this we are indebted for the arrival, in our winter (which is a kind of summer to them), of such valued birds as the woodcock, snipe, widgeon, &c. On the other hand, birds of the south, whose food is most plentiful in the winter of their respective countries, travel northwards when summer comes, and find, in our comparatively cool summer, a temperature suited to their wants, and answering, in some degree, to the winter season of the land which they have quitted. It is a curious fact, that a few of these birds are sent as precursors of the main body; hence our proverb, "One swallow does not make a summer."

The winter sleep of animals, called hybernation, would seem to depend entirely upon the action of cold; but this we are told is an error. The influence of cold in the matter is only that of inducing

a kind of sleep, which may be called the first stage of hybernation; but there must be other causes at work before this sleep passes into the state truly called hybernation. The torpid sleep produced by cold is often fatal to life; but the condition of animals during their winter sleep is not opposed to health. It is remarkable, also, that while moderate cold is favourable to hybernation, intense cold is unfavourable to this condition, and has the same effect in rousing the animal from its sleep as any considerable amount of heat would have. On the

other hand, the term sommerschlaf, or summersleep, employed in Germany, shows that there is a lethargy induced by warmth; and Cuvier speaks of some animals, inhabitants of the torrid zone, that pass three months of the year in a lethargic state. In passing from ordinary sleep into the state of hybernation, the respiration becomes weak, and the temperature is many degrees lower than when in an active state. The whole phenomena, and their relation to temperature, are deeply interesting subjects of investigation.

The power of many of the inferior tribes of animals to endure cold is very remarkable. It is supposed that the mosquitoes, which appear fullgrown in the earliest part of spring, are not the produce of that season, but have remained in a frozen state during the winter. This is known to be the case with many others of the insect tribe. Mr. Ellis mentions a black frozen mass of a turflike substance, which, when thawed, produced a

swarm of mosquitoes; and Hearne says, that spiders frozen so hard as to bound from the floor like a pea, were revived by being brought to the fire. Leeches, snails, grubs, and frogs, have been frozen by cold and revived. Hearne has noticed that frogs burrow under the moss at a considerable distance from the water, where they remain in a frozen state till the spring. He has frequently seen them dug up with the moss, frozen as hard as ice; in which state the legs are as easily broken off as a pipe stem. By warmth they regain their usual activity; but if permitted to freeze again, they are past all recovery. Hood noticed that on the melting of the snow, the noise made by the frogs was almost incredible; nor is it possible, he remarks, that the multitude, which incessantly filled our ears with its discordant notes, could have been matured in two or three days of spring. Captain Franklin also mentions a curious fact with regard to fish:-"The fish froze as they were taken out of the nets, and in a short time became a solid mass of ice; and by a blow or two of the hatchet were easily split open, when the intestines might be removed in one lump. If in this completely frozen state they were thawed before the fire, they recovered their animation. This was particularly the case with the carp; and we had occasion to observe it repeatedly, as Dr. Richardson occupied himself in examining the structure of the different species of fish, and was always, in the winter, under the necessity of thawing them before he could cut them. We

have seen a carp recover so far as to leap about with much vigour, after it had been frozen for thirty-six hours."

The effects of continued and severe frosts in the preservation of animal substances are well known. The cause of science has been served by the discovery of animal remains of past ages, embedded in frozen sand, and in ice which never thaws. The entire carcase of a mammoth was thus preserved on the banks of the river Lena, and discovered by a fisherman in 1799. The flesh was in such a state of preservation, that it was devoured as it lay by wolves and bears, and hunters' dogs. A great quantity of hair and bristles covered the skin, and some of this has been preserved in our Hunterian Museum at the College of Surgeons. The account of this animal and its discovery is to be found in the memoirs of the Academy of Sciences at St. Petersburg, and a translation of the same has been published in London. The bodies of whales have been found imbedded in icebergs, and so well preserved, that in one case, notwithstanding the unknown length of time which must have elapsed since its imprisonment, the body yielded large quantities of oil.

The effects of cold on vegetable life are in many respects similar to the effects produced in the animal world. Growth is stunted, species are limited, yet no land in the Arctic regions has yet been discovered which is entirely destitute of vegetable life. It is different in the Antarctic

lands which are scattered round the south pole. On these the vegetation decreases as the latitude increases, till, long before reaching the polar circle, a land of desolation is arrived at. Not a lichen covers the storm-beaten rocks, not a seaweed, save a few microscopic marine plants, lives in the sea. This great difference seems to arise from the want of warmth in summer. In the brief summer of high northern latitudes, the sun has considerable power; but in corresponding southern latitudes the thermometer does not rise above 14° Fahrenheit at noon, at a season corresponding to our August. Lichens, mosses, and other cryptogamous plants, form the chief vegetation of Arctic lands; in sheltered spots the service tree bears fruit, and the birch may grow to the height of a few feet, but woody plants in general trail on the ground. In Nova Zembla and the far north, the birch, the willow, and a few berry-bearing shrubs, trail along the ground, never rising more than an inch or two above the surface. A species of willow (salix lanata), which has been called the giant of these small forests, has a stem ten or twelve feet long, but this it trails on the ground where it is half hidden in moss, while the branches do not rise more than five inches high. The same kind of diminution in size and variety which marks the vegetable world as we approach the poles, is also observable in ascending mountains of great elevation.