tains a mean heat much above that of the incumbent atmosphere, and still more above that of the land. During winter and spring the difference between the temperature of the ocean and of the earth's surface, in this latitude, is very great, and is heightened, at these seasons, as well as in others, by the flow of the inter-tropical waters from the south-west to the north-east; the edge of this great current sweeping along the shores of Ireland, and slightly influencing the Irish Channel, so as to constitute what is known to navigators by the name of the inset of this channel; and thereby tempering the climate of that island, as well as that of the southern and western sides of Great Britain.

It must be evident that the physical circumstances already adduced explain not only the prevalence of certain winds, and the variations of temperature observed to follow every change in the atmospheric current, but also, in a great measure, the comparative dryness and humidity of the air, and the deposition of the exhaled moisture in the states of snow, rain, fog, and dew. The quantity of moisture which the air will retain, without affecting its transparency, varies very remarkably with its temperature. Sir John Leslie ascertained, that air, at the freezing point, is capable of holding a portion of moisture equal to 160th part of its own weight; at the temperature of 59°, the 80th part; at that of 86°, the 40th part; at 113°, the 20th part; and at that of 140°, the 10th part; so that the air has its dryness doubled at each rise of temperature answering to 27° of Fahrenheit. While the temperature, therefore, advances uniformly in arithmetical progression, the dissolving power which this communicates to the air mounts with the accelerating rapidity of a geometrical series. It follows, that when the air, at any given temperature, is saturated with moisture, a depression of temperature will make it yield a portion of such moisture. proportioned to the depression; the moisture thus parted with assuming various forms, according to the elevation at which the separation takes place, and the rapidity with which the change of temperature

occurs.

From the above it follows, that the amount of evaporation, or, more correctly, the quantity of moisture which the air will retain without affecting its transparency, must depend chiefly upon its temperature. Mr. Howard and Mr. Daniell have endeavoured to ascertain this in respect of the vicinity of London, and the results of their inquiries very closely accord. The average annual amount of evaporation, according to Mr. Daniell, is 23.974 inches, and the rate at which it proceeds during the several months of the year is estimated by him as follows:

Thus the average monthly amount of evaporation increases and diminishes with the temperature. The average annual amount of rain that falls in the neighbourhood of London is, according to

Mr. Daniell, very nearly the same as the annual amount of evaporation, or 23 inches; the several months contributing the following

When we observe the immense oceanic surface to the west and southwest of the British Isles, the humidity of the winds blowing from these directions must be anticipated; and when we remark the extensive continent to the east, and its comparative dryness in spring and summer, and more especially in winter, when the earth's surface, with its rivers and lakes, is congealed into an icy crust, and the moisture of the air is precipitated in the states of hail, snow, or hoar-frost, the dryness of the east winds must be equally obvious. The moist and warm winds from the former directions deposit their moisture in the form of rain, when changes of temperature and electrical conditions diminish the solvent property of the atmosphere, particularly when the temperature of the land sinks below that of the adjoining ocean, and when the air is thereby cooled as it passes to the east. Hence the principal part of the rain in England is from the west, about twothirds of the whole quantity falling on the west side of the kingdom. During spring, when north-east winds prevail, in consequence of the change in the sun's declination, and the much greater warmth of the Atlantic Ocean, the dryness of the air, owing to the circumstances stated above, is often remarkable; and when these winds begin to blow, they generally precipitate, by their great coldness, the moisture as it rises from the warmer surface of the earth, or surrounding waters and lakes, in the form of fogs or mists; and are often the cause of the catarrhal, bronchial, pulmonary, rheumatic, and aguish affections prevalent at this season, more especially when they pass over low, humid, and marshy grounds, as in various parts of Essex, Cambridgeshire, &c.

During summer and autumn, westerly winds are most prevalent. The air from the Atlantic Ocean rushes to replace the strata constantly rising from the heated surface of the inland countries of Europe, and deposits the moisture with which it is loaded, in the form of rain, as it passes over the nearest land; the mountains, hills, and places in their vicinity, which first attract the clouds formed by the exhaled moisture, experiencing the greatest fall. Still the air does not thus lose all its moisture, but only that part which the change produced by the terrestrial radiation in its temperature and electricities, renders it incapable of holding in solution; and the atmospheric current, in its course eastward, often parts with other portions, until it has its solvent properties again increased, by the greater heat of the European continent in these seasons; and the rains are replaced by nightly falls of dew, as the nocturnal cooling of the earth's surface lowers the temperature, and also the solvent powers, of the adjoining stratum of air.

When, however, the southern declination of the sun at the end of autumn reduces more permanently the temperature of the earth's surface, the air, being consequently cooled, precipitates a large portion of its moisture; and, at the same time, its lower stratum rushes westward, to replace the stratum elevated into its higher regions from the now warmer surface of the Atlantic; whilst this latter stratum, in the higher regions, rushes eastwards, and, as it cools, replaces that which is attracted westward by the cause now assigned; a circulation of the atmosphere from east to west in the lower, and from west to east in the upper stratum, being thus established. It is chiefly owing to this circumstance that falls of rain often take place from the east during the latter part of autumn and commencement of winter: the moisture which, in spring and summer, had passed over this country, either dissolved in the air, or suspended in the form of clouds, and been conveyed to the dry and comparatively warm atmosphere of continental Europe, returning again over Great Britain, and giving rise. to prolonged rains or fogs, as the currents and solvent powers of the air change with the varying position of the sun, and with the different degrees of temperature of the earth's surface and of the ocean, at the same latitude. A large portion, also, of the rain which falls when the winds blow from easterly quarters, is owing to the circulation of the warm and moist air from the surface of the ocean into the higher regions, and thence eastwards, where it passes into the lower regions as it cools, and replaces that which flows westwards and afterwards rises from the warmer surface of the ocean; the moisture thus exhaled from the Atlantic not being altogether deposited in the form of rain or snow until it has nearly gone the circuit now pointed out.

It is seldom that a considerable fall of rain takes place with the winds at north-east or east, particularly during winter and spring, unless they veer towards the north or south, or unless the clouds formed by the moisture exhaled from the ocean move in the higher regions of the air in a westerly direction, and, as they become further cooled by the land, either change their course, in the manner just stated, or impart their moisture to the lowest stratum of air circulating in an opposite or different direction. Thus, we generally perceive that rain from the east, or, rather, with the wind at east, is preceded by large clouds or haziness of the air, rising from some quarter connected with the west; and that, although the wind may still continue to blow from the east, these clouds extend, rise out of the western horizon, and move rapidly to the east, until the atmosphere becomes thick in all directions; the clouds supplying the falls of rain from the east actually coming from the west, and depositing their moisture in the course of that circulation explained in the preceding paragraph. Those who have been led by their occupations to note the changes of the atmosphere never expect the cessation of rain from the east until the western hemisphere becomes clear, or the clouds cease to rise from that quarter; nor trust to any continuance of dry weather, if heavy clouds rise and move in a different direction from that in which the wind is blowing at the time.

The other physical circumstances enumerated above, as influencing

a favourable effect. The elevation of particular districts is nowhere so great as very remarkably to affect the temperature, or dryness of the air. The range of hills extending southwards from Cumberland and Westmoreland tends, however, to increase the quantity of rain which falls in their vicinity, or in places situated near their bases; and a similar effect is produced by the Welsh mountains. But the geographical and other physical circumstances of the west side of the island would cause a greater fall of rain to take place on it than on the east side, though no such ranges of hills existed. The extent, however, to which they may operate in producing this result, will appear more fully in the sequel; but more influence seems to have been imputed to them than they really exert.

Proximity to the sea has a very marked effect upon the climate of England, but chiefly in the way already shown." This is felt throughout the kingdom, but principally near the coast, and more especially on the south-west coast ; the daily, monthly, and yearly ranges of the thermometer being, through the vast extent of the circumjacent ocean, very much limited; while the humidity of the air is at the same time increased. The tempering effects of the sea on the east side of Great Britain are very much less than on the west. The sea off the former is cooled in winter and spring by the waters of the Germanic rivers, which are poured into it at a temperature little short of the freezing point; whilst that off the latter is influenced by the constant flow of the Atlantic towards the polar seas, as stated above. The temperature of the waters of the Irish channel, even in January, seldom falls below 50° Fahrenheit; and that of the Atlantic, in the same latitude, is very considerably above this; whilst the German Ocean, in the same season, is several degrees below 50°: it seldom, indeed, rises above 45°, excepting in July, August, and September.

The geology of England exerts, on the whole, but little influence upon the climate, excepting in as far as it contributes to form the soil and to determine cultivation; and it is nowhere such as can injuriously affect the atmosphere. The face of the country, with few exceptions, is sufficiently undulating to facilitate the percolation of superabundant moisture, and to favour its flow into adjoining rivers; and it is only in certain limited tracts, on the east side of the kingdom, where the soil is deep, absorbent, or marshy, as in parts of Cambridge, Lincoln, Suffolk, Huntingdon, Norfolk, and Essex, and in a few places in Kent and Sussex, that the moisture is retained until it is altogether evaporated into the air, carrying with it a portion of decayed vegetable or animal matters, or the gases formed by their decomposition.

The cultivation of the country has either wholly removed or materially diminished most causes of insalubrity, and increased the favourable influence of the circumstances already specified upon the climate. The temperature of some countries is much reduced, the humidity of the air increased, and the sources of disease multiplied, by extensive forests and the neglect of tillage; but such is not the case in England. Our woods are neither large nor thick enough to have any pernicious influence; and our improved system of agriculture has helped to

counteract the physical causes that render the atmosphere more moist than in continental countries. In some parts, particularly in the eastern counties, large marshy districts have been drained and cultivated, and rendered drier and warmer, as well as more salubrious, than formerly. In a few places, however, where canals have been multiplied, and extended through tracts where they could not, from their level and other circumstances, drain off superabundant moisture, the climate has been deteriorated. But, while railroads form so rapid and so attractive a means of public conveyance, canals are not likely to be much further multiplied; and, after all, their injurious influence upon the climate is, even at present, but little felt, and limited to a few places only.

The general results of the circumstances reviewed above, upon the climate of England, are―(a) the moderation of extremes of temperature; (b), a humid state of atmosphere, more remarkable, however, near the sea coast than in the more inland parts, and on the south-west and west sides than on the east ;-(c), an uncertain and changeable state of the seasons; -(d), very frequent vicissitudes of atmospheric temperature and humidity, owing chiefly to changes of the winds; -(e), a limited range of these vicissitudes, even when they are most frequent; and (f), a more equable and milder climate, although more humid and more changeable, within certain limits, than that of any other country placed at the same distance from the equator. Certain of these results require illustration.

a. The temperature is so moderated in its extreme ranges, that it seldom falls much below the freezing point, even in the month of January, the coldest month,―very rarely so low as 18° or 20°, and hardly ever to either of these degrees, excepting in the more inland counties, and on the east side of the kingdom; or rises above 78° or 80°, or even so high, unless in the south-east and inland places, in the warmest months of July and August. In the northern parts of the kingdom, owing to their nearer proximity to the ocean, the extremes of temperature are still more contracted, the thermometer seldom falling to, and very rarely lower than, the limits now specified; and hardly ever rising above 75°. So that, upon the whole (excepting where difference of elevation above the level of the sea makes a slight variation), the mean annual temperature of the northern parts of the country is only between 2° and 3° lower than that of the south-eastern counties; the more moderate heat of summer and autumn, in the former, being compensated in part by a less extreme or permanent degree of cold in winter than is occasioned in the latter by proximity to the Continent; and the greater distance of the northern counties from the equator being, in some measure, counteracted by the tempering influence of the ocean. The difference, however, between the annual temperature of the northern and the southwestern and inland counties is much greater than that between the northern and south-eastern; owing to the more distant removal of the south-western counties from the continent of Europe, and their nearer proximity to the equator. In the midland counties (and especially in the more southerly of these), the heating effects of