district, the myrtle, the Camellia japonica, the Fuchsia coccinea, the Buddleia globosa pass the winter without shelter in the open ground, and orange trees are seen on espaliers, only sheltered, as at Rome, by means of matting. On the coasts of Brittany, in the department of Finisterre, the arbutus, the pomegranate tree, the Yucca gloriosa and Aloifolia, the Erica Mediterranea, the Hortensia, the Fuchsia, and the Dahlia, resist in open ground the winter, the mean temperature of the peninsula being above 56° 3'; and Humboldt states, that in the interior of France, where the land is not much elevated above the sea, we must go south 3° of latitude in order to find an annual temperature equal to it. The milder winter of places on the Atlantic coast of France, as compared with interior situations of corresponding latitudes, appears from the table:

Interior countries likewise, which abound with rivers, lakes, and marshes, are less subject to the extremes of heat and cold than those which have an opposite physical character. The heat experienced upon the well-watered plains of Hindûstan is never so excessive as in the dry corresponding regions of Northern Africa; and around the Canadian lakes, the winter is milder than in other localities under the same latitude. There is an anomaly in climate, which is very satisfactorily explained by a reference to the temperature of the adjoining ocean. This is the well-known fact, that in travelling from the equator northward to the pole, the cold increases in a slower ratio about the meridian of London, than in any other part of the world. The climate of western Europe in general is milder than that of countries under the same parallel at its eastern extremity, or in Asia, or in America. The decrement of the mean annual temperature in Western Europe and in North America, prolonging the scale to the equator, is given in the following table from Humboldt::

Thus, at the latitude of 40°, that of Madrid and Philadelphia, the mean annual temperature of Western Europe is 9° higher than that of North America. At latitude 60°, that of St. Petersburg, Upsal, Christiania, South Shetland, the south point of Greenland, the north point of Labrador, and the lower extremity of the Great Slave Lake, it is 16° higher, and 33° higher at latitude 70°. A similar difference appears in favour of Western Europe comparing it with Eastern Asia.

It is also the case, that the western region of North America, between the Rocky Mountains and the Pacific Ocean, is warmer than the eastern between the Alleghanies and the Atlantic; and it was once imagined, that, comparing the two sides of the Alleghany mountains, the country to the westward, including the states of Ohio and Tenessee, and

the vast basin of the Mississippi, had a milder climate, than the Atlantic states to the eastward, under the same parallels. But the mean temperature is nearly equal on the east and west of the range; and the more northerly migration of certain vegetables on the western side, which originated the surmise, is referable to the Mississippi valley, lying in that direction, favouring their transport, while in the eastern provinces the valleys are transverse, and consequently offer no facility to their passage to the north. It cannot, however, be doubted, taking the whole continent into consideration, that the eastern districts of North America are colder than the western; and in proceeding from Western Europe, in an easterly direction, there is a gradual increase of cold experienced. Thus at St. Petersburg it is 3° colder than at Upsal on the same parallel, and 5° colder at Moscow than at Copenhagen.

It is an interesting point to determine the cause of the greater warmth experienced under the meridian of London, and through the whole of Western Europe, than in corresponding latitudes. There can be no doubt that the solution is to be found in the warm water of the Gulf stream in the North Atlantic, and the prevalence of west and southwest winds. We have before referred to this remarkable current of warm water, not inferior to the Mediterranean in its extent, which sweeps through the ocean towards the continent of Europe, having a temperature from 3° to 10° higher than that of the contiguous sea. The winds that blow over it have its character impressed upon them, and rush up from the west and south-west, invading Europe from Cape Finisterre to the North Cape with currents of warm air, reaching into the heart of the continent to the plains of Russia, through the great gate between the Scandinavian and the Harz mountains. It may be objected to this, that the Gulf stream ought in a similar manner

to warm the Atlantic States of America by which it sweeps, whereas the mean temperature there is lower than in Western Europe; but this is owing to the narrowness of the current in that quarter, and to the prevailing winds being from the west and south-west, which carry the hot circumambient air away from the shore. With reference to the lower degree of heat experienced over the whole continent of America, as compared with corresponding latitudes in the eastern portion of the earth, Humboldt advances the following statement in his Tableaux de la Nature: "The comparative narrowness of this continent-its elongation towards the icy poles-the ocean, whose unbroken surface is swept by the trade winds -the currents of extremely cold water which flow from the straits of Magellan to Peruthe numerous chains of mountains, abounding in the sources of rivers, and whose summits, covered with snow, rise far above the region of the clouds-the great number of immense rivers, that, after innumerable curves, always tend to the most distant shores-deserts, but not of sand, and consequently less susceptible of being impregnated with heatimpenetrable forests, that spread over the plains of the equator, abounding in rivers, and which, in those parts of the country that are the farthest distant from mountains and from the ocean, give rise to enormous masses of water, which are either attracted by them, or are formed during the act of vegetation :-all these causes produce, in the lower parts of America, a climate which, from its coolness and humidity, is singularly contrasted with that of Africa. To these causes alone must we ascribe that abundant vegetation, so vigorous and so rich in juices, and that thick and umbrageous foliage, which constitute the characteristic features of the new continent."

4. There are various other circumstances which enter into the constitution of climate, such as the soil of a country, whether light and porous, or clayey and compact, whether open to the solar action and to the play of the winds, or covered with forests, and screened by mountains from the free operation of atmospheric currents. Barren sands admit of a much more intense heat than a loamy soil, and pasture lands are not so susceptible of it as the bare ground. The clearing of a country from trees has the effect of raising the mean annual temperature, but at the same time greater extremes of heat and cold are introduced. Dr. Williams found the temperature of open grounds 12° higher in summer and 7° lower in winter, than that of forests. Open grounds are always frozen deeper than the woodlands, and hence the spring advances later; but being more heated in summer, the winter commences later. Several countries have, however, suffered severely from the incautious destruction of the forests, having been deprived thereby of a natural protection needed by their geographical position from the intensity of the solar rays, or from the heated air of neighbouring districts, besides the amount of moisture in the atmosphere being lessened by the loss of the vegetation which promotes evaporation. The climate of some parts of Southern Europe has been deterioriated from this cause, and the oppressive heats and dreadful droughts of the Cape Verde Islands are due to it. In addition to the direct effect of the sun's rays, contiguous parts of the earth exert a continual influence upon each other, by reciprocating their temperature through the medium of the winds. In this way, the deserts of Arabia and Africa are like immense furnaces warming all the regions on the Mediterranean Sea, in the south of Europe and the west of Asia; and in a similar manner, the mountains and table-land of Tartary increase the cold of the surrounding countries. At Bagdad and at Bushire, where the south wind arrives heated by the burning sands of Arabia, the thermometer sometimes stands at 125°, and on the west coast of Africa, when a similar cause operates, it has been observed at 130°. In the August of 1819, when the fierce simoom blew at Bagdad, the thermometers rose to 120° in the shade, and at midnight were at 108° in the open air, and a heavy rain falling, an unprecedented event, the whole region was converted into a vast hot steam-bath. Multitudes of people, both in the country and in the streets, dropped down dead, owing to the intense heat. A

small caravan lost twenty-two persons in this manner during the last three days of its journey across the Desert towards the city.

In the United States, the prevailing winds remarkably affect the temperature, producing the cold of the polar regions and the warmth of the torrid zone, according as they blow from the frozen shores of Hudson's Bay or from the hot regions of the Gulf of Mexico. In Venezuela, the temperature, which is from 87° to 90° in March, rises to 104° or 105°, whenever the wind blows from the parched surface of the llanos or great plains. Siberia, and the northern parts of North America, have their cold greatly increased by the polar winds, which are not intercepted by mountains, in addition to the effects of a northern declivity. But the same wind, in various countries, will produce opposite effects upon the temperature at different seasons of the year. Poeppig mentions a singular instance of this in the southern districts of Chili. The east winds, called los Puelches, blowing in spring, are so cold as rapidly to depress the temperature 15° or 18°; but towards the end of summer they raise it nearly as much. The former effect is attributed to the deep snow lying in spring upon the Andes chilling the adjacent air, and the latter to the heat which the sandy pampas of Buenos Ayres acquire in the summer months. The east winds of England exhibit this alternating character. Late in spring, having passed over the plains of the Baltic, yet bearing the chill of winter, they are cold; but in autumn, they are warm enough to raise the temperature, the sandy plains in their passage having been heating through the summer.

The preceding causes are those by which physical climate is chiefly determined. A few results of observation respecting the mean annual temperature in different localities, and seasonal temperature, may now be stated, chiefly upon the authority of Humboldt, Dove, Kaemtz, and other meteorologists.

The mean temperature of a locality is the average of heat and cold throughout the year, and may be obtained by observing at stated periods, during each day, the indications of the thermometer, taking a series of such observations continued through an interval of ten or fifteen years. This is a tedious and protracted process, and the lessons of experience have superseded the necessity for it to some extent. Thus, the mean temperature of the

day may always be obtained by three readings of the thermometer, namely, at sunrise, at two o'clock in the afternoon, and at sunset; and then dividing the sum of the temperatures by three. When the mean temperature of all the days of the month has been found, the sum of the diurnal temperatures divided by the number of days, gives the mean temperature of the month. In like manner, the sum of the mean monthly temperatures in the year divided by the number of months, gives the mean temperature of the particular year. By comparing a series of these annual returns, and striking the average, the standard annual mean temperature of a place is deduced. It is a curious and highly useful result of thermometric observation, that at many places in the north temperate zone, where alone meteorological notices have been multiplied, the mean temperature for the months of April and October is identical, or very nearly so, with the mean temperature of the year. The close approximation of the mean temperature of these months to the annual mean is apparent from the comparison in the table; and is most conspicuous with reference to October.

In almost all northern latitudes, January or February is the coldeɛt month of the year, and July or August the warmest. The greatest cold during the day is usually about an hour before sunrise. The greatest heat in latitudes between 35° and 60° is from two to three o'clock, and from one to two o'clock between the equator and 35°.

The mean temperature of different months, in various places, takes a very wide range above and below the mean annual temperature, and constitutes what Buffon has indicated by the name of "excessive" climates, where the winter and summer are in violent contrast. These are chiefly found in North and Eastern Europe, in Asia and America.

The climates of the northern United States, Canada, a great part of Russia, and northern China, are among the most " excessive," the winters and summers strongly contrasting in their temperature. Thus, at New York, says Humboldt, we find the summer of Rome and the winter of Copenhagen. At Quebec, grapes sometimes ripen in the open air, whereas the winter is that of Petersburgh, during which the snow lies five feet deep for several months, and travelling is performed in sledges, frequently on the ice of the St. Lawrence. At Pekin in China, where the mean temperature of the year is that of the coasts of Brittany, the scorching heats of summer are greater than at Cairo, and the winters as rigorous as at Upsal. These violent contrasts render such climates trying to the constitution of a western European, unused to such extremes of temperature, the excessive heat of summer, after the rigour of winter, increasing the irritability of the nervous system.