Although this table presents more than one anomaly, it yet shews very evidently the influence of continents. Notwithstanding the very high latitude of Cuxhaven, Lunenburg, and Apenrade, the mean of the winters is above the freezing-point. This is in consequence of the vicinity of the sea, counterbalanced, however, by the continental influences, which reduce their mean below that of the towns of England situated under the same latitude. In all other parts of Germany, the winter mean is below the freezingpoint; but the summers are also hotter, as may be seen by comparing the table of England with that of Germany, keeping in view the height above the level of the sea. There results from this a greater difference between the winter and the summer; it is 16° in west Germany, in the neighbourhood of the sea, and rises as high as 20° in the east part. At Dantzic, the feeble influence of the neighbourhood of the Baltic is felt.

The more we penetrate into the interior of the continent, the colder do the winters become; and the more does the difference between winter and summer tend to increase, as the following table shews:

WINTER AND SUMMER TEMPERATURES IN THE INTERIOR OF THE CONTINENT.

Whilst in England the thermometer rarely descends 10° below zero, we find in the interior of the continent, under almost equal latitudes, a mean of -10°; and it is not uncommon to see the mercury freeze at Kasan. In the interior of Siberia, it often remains solid for several weeks together. The serenity of the sky in these countries favours the radiation of the ground in winter, and its heating in summer; so that the summers are hotter than in Eng

land. The difference between the means of the two seasons, which is 23° in west Russia, is as great as 33°, and even 56°, in the interior of the empire; it is, therefore, four or five times greater than in England.

This law prevails every where. The west coast of Norway enjoys a winter relatively very mild, and the mean of which does not differ one-tenth of a degree from that of the summer. But scarcely have we traversed the crest of the Scandinavian Alps than we find a continental climate. The same relations prevail in North America. Whilst the west coast is distinguished by mild winters and cold summers, the difference of the seasons is greater in the interior; it then diminishes as we approach the Atlantic. However, it is always greater than in Europe. This is due to the predominance of west winds, which, as they traverse a great extent of land, communicate to the climate of these countries something of continental climates. Thus, in east America, the winters are colder and the summers warmer than they would be were it not for this circumstance.

ISOCHIMENALS AND ISOTHERALS.—If we collect into a map all the places whose hibernal mean is the same, we shall obtain curves called isochimenal (iros, equal; xv, winter). These which pass through the points, where the summer means are equal, are called isotherals (ïoos, equal; igos, summer). The number of observations is not yet sufficiently large to enable us to trace these curves with perfect exactitude; but they are sufficient to shew that these lines are far from coinciding with the parallels which join the places, and which are situated at the same distance from the equator; for the isochimenal lines fall toward the south, as we leave the west coast of Europe on our way toward the east; because the countries situated toward the cast have much severer winters than those that are at the west. The isotherals, on the contrary, rise toward the pole as we go from west to east; and it is only in the interior of the continent that, at equal latitudes, the summer means are the same. In North America something similar is observed; for, at an equal distance from the equator, places situated west of the Alleghanis have colder winters and hotter summers than those which are on the borders of the sea.

We may easily comprehend that these climateric conditions have the greatest influence over the geographical distribution of organised beings. Many animals, especially quadrupeds, that cannot make such great migrations as birds, avoid extreme climates. If, therefore, a curve is passed through the points which limit on the north the area

inhabited by these animals, this curve will almost coincide with an isochimenal. This is shewn in the chart published by M. Ch. Ritter, on the distribution of wild and domestic mammifera in Europe. Thus, in Sweden, the elk still lives under 65° of latitude; but, in the interior of Siberia, it does not pass the 55th degree.

The same observations apply to the distribution of vegetables on the earth; but we must carefully distinguish arborescent vegetables from those which are merely annuals, and die each year after having produced seed. Trees cannot so effectually resist the rigours of winter as perennial herbaceous vegetables; however, if their period of flowering and fructification is not long, they rise even to high latitudes along the coasts of the Atlantic, while they remain much nearer to the south in the interior of the continent. Thus, in the neighbourhood of Penzance, on the west coast of England, myrtles, Camelia, Fuschia and Budleia, pass the whole winter in the open air, although their fruits do not ripen in summer. The coasts of Brittany present the same phenomena. The beech (Fagus silvatica) extends in Norway as far as the 60th degree. On the west coast of Sweden its extreme limit is below the 58th; in Smoland, at 57°, and also on the east coast in the neighbourhood of Calmar. In Lithuania, it is between 54° and 55°; in the Carpathians, about 49°; and in the mountains of the Crimea, about 45°. The holly (Ilex aquifolium), which advances even as far as Scotland and Norway, is sometimes frozen in the neighbourhood of Berlin and IIalle. Several kinds of

heath, alder, black poplar, lilac, ivy, mistletoe, thorn, and myrtle, have an analogous geographic distribution.

The small table that follows represents the indication of the latitudinal limits of many trees in Scandinavia :—

For further details, see the note entitled, "On the distribution of large Vegetables along the coasts of Scandinavia, and on the north side of the Grimsell." (Annales des Sciences Naturelles, Oct. 1842.)-M.

Annual vegetables, and especially those of the corn tribe, act in a different manner. The hardness and rigour of the winter little concerns them; the only thing essential to them is the period during which they are developed; thus the curves that indicate their northern limits are parallel to the isotherals. In Norway, barley is cultivated in certain places situated under the 70th degree. Toward the east, its limit falls southerly; and in Siberia none of the corn tribe are found north of 60°. In France, the north limit of maize is determined by the same laws. On the borders of the Atlantic it is south of Rochelle, at 45° 30′; but on the Rhine it is between Manheim and Strasburg, at 49° of lat.

The arborescent vegetables which are not very sensible to the colds of winter, but which require hot summers, have, on the west coast of Europe, a limit dependant on the curve of the isotherals. Thus the vine is no longer cultivated with advantage on the coasts of France beyond 47° 30'. In the interior of the country it rises toward 49°, and cuts the Rhine at Coblentz at 50° 20'. In Germany, it does not pass 51°, to which it is sensibly parallel in the east of the European continent.

MEAN TEMPERATURE OF THE EARTH.-Before studying the distribution of heat on the surface of the globe, it is necessary to give a table of the mean temperatures of a great number of places on the earth.*

* We have substituted for M. KAEMTZ's table the more recent and extended one of M. MAHLMANN, who has recalculated all the means with the greatest care.8

This table is extracted from the third volume of the important work which M. DE HUMBOLDT has just published, on Central Asia, under the title of Researches on Mountain Chains, and Comparative Climatology.

In this table the seasons are those used in meteorology, namely, for winter, December, January, and February; for spring, March, April, and May; for summer, June, July, and August; for autumn, September, October, and November. The temperatures enclosed between a pair of brackets do not merit so much attention as the others. The number of years of observation is generally related to the annual mean. The heights above the level of the sea are in metres, as in the whole course of the work.-M.

8 Vide Note g, Appendix, No. II.