distantly situated, and noted by different persons; thus they may not be observed at precisely the same period, and this, should they happen to be rising or falling rapidly at the time, would introduce some error; again, at the time of observation, one person may give a tap with his finger to the tube-the other may not, which will sometimes make a difference of some hundredths, the mercury, often adhering slightly to the glass, resuming its proper indication when gently moved or shaken.

From these considerations, (to say nothing of the probable error in printing three different decimal figures thirty times every month) we feel much inclined to conclude that the fluctuations of the barometer at London and Malvern are simultaneous, and very nearly (quite?) equal, and, if so, of course in all places intervening.

In September, the first month of the autumnal quarter, the maximum of the barometer, in London, was 30.461, the minimum 29.315; the mean 30.026, and the range 1.146 inch. In Malvern the maximum was 29.877, the minimum 28.740; the mean 29.425, and the range 1.137.

In October, the maximum, in London, was 30.619, the minimum 29.237; the mean 29.996, and the range 1.382. In Malvern the maximum was 30.027, the minimum 28.734; the mean 29.401, and the range 1.293.

In November, the last month of the autumnal quarter, the maximum of the barometer, in London, was 30.379, the minimum 29.141; the mean 29.904, and the range 1.238. In Malvern the maximum 29.883, the minimum 28.586; the mean 29.331, and the range 1.297.

For the autumnal quarter

Mean Height.

London....29.975.
Malvern ......29.385.

DEW-POINT.

Mean Range.
1.255
1.242

The atmosphere being everywhere mingled with aqueous vapour of very variable elasticity, and upon which all those important meteorological phenomena rain, cloud, mist, dew, &c., primarily depend, it is necessary, in any comparison of climates, to estimate the changes it is daily undergoing. The hygrometer enables us to do this-particularly the one now well known as Daniell's Hygrometer. In the Meteorological Tables published by the Royal Society, there is a column including the dew-point, every morning at 9, A. M. and we are in possession of similar observations at the same hour made at Malvern, and both determined by the above instrument.*

* It would be almost impossible to describe this delicate instrument so as to be understood without a plate and references; the result is obtained by gradually lowering the temperature of a dark glass bulb, until a thin ring of dew or moisture is deposited upon it. The precise point at which a thermometer, affected by the process, stands when this appears, is termed the dew-point, or point of condensation, which marks with infallible precision, the comparitive degrees of moisture and In June, the maximum dew-point was, in London, 62,° the maximum in Malvern also 62.° The minimum dewpoint, in London, 45,° in Malvern, 43.° The mean, in London, 51.5,° in Malvern 51.1.

In July, the maximum dew-point, in London, was 69, the minimum 54,° and the mean 59.4.° In Malvern, the maximum 68, the minimum 50,° and the mean 55.8.°

In August, the last month of the summer quarter, the maximum dew-point, in London, was 67, the minimum 49, and the mean 59.1. In Malvern, the maximum 64.5, the minimum 47.5, and the mean 55.8.°

Taking the mean temperature of the summer quarter, and the mean dew-point, as data, we are enabled to estimate

London. Malvern. The mean elasticity of the vapour in the air (for the season) ..0.492 in...0.460 in.

The mean weight of vapour (in grains) in a cubic foot of } ..5.400....5.112

air (for the season)

Thus we find, as would be expected, a less quantity of vapour in the higher locality than in the lower during the summer months. In the month of September, the first of the autumnal quarter, the maximum dew-point, in London, was 64, the minimum 47, and the mean 55.8.° In Malvern, the maximum 57, the minimum 49.5, and the mean 52.8.°

In October, the maximum dew-point, in London, 60,° the minimum 26, and the mean 48.7.° In Malvern the maximum 55, the minimum 37, and the mean 46.3.°

In November, the last month of the autumnal quarter, the maximum, in London, was 58, the minimum 34, and the mean 43.6.° In Malvern, the maximum also 58,° the minimum 28.° and the mean 40.5.°

dryness in the atmosphere, and by exhibiting them in degrees of the thermometer, refers them to a known standard of comparison. By means of appropriate tables, the weight and elasticity of the invisible vapour of the atmosphere may be determined.

The hygrometer, when consulted with a view of predicting the greater or less probability of rain, or other atmospheric changestwo things are principally to be attended to, the difference between the temperature of the dew-point, and the temperature of the air, and the variations that may occur between them. In general the chance of rain, or other precipitation of moisture from the atmosphere, may be regarded as in inverse proportion to the difference between the two thermometers, one marking the dew-point, the other the temperature of the air. An increasing difference, accompanied with a fall in the former, is an almost sure prognostic of fine weather; whilst a diminution in the temperature of the air, and a rising dew-point, portend rain. In winter, when the differences between the dew-point and the temperature of the air are always small, the indications must be taken more from the actual rise and fall of the dew-point, than from the difference between it and the temperature of the air. A sudden change in the dewpoint is generally accompanied by a change of wind, and the former sometimes precedes the latter by a short interval; and the course of the ærial current may then be anticipated before it affects the direction of the weathercock, or even the passage of smoke. A rise in the dew-point, accompanied with a fall of the barometer, is an infallible indication that the whole mass of the atmosphere is becoming imbued with vapour, and a copious precipitation may be expected. If a fall in the barometer, and a fall in the temperature of the dew-point, take place at the same time, we may conclude that the expansion which occasions the former has arisen at some distant place, and wind, not rain, will be the result.*

WIND.

In comparing the direction of the wind at Malvern with that in London, we have adopted a very easy, but not perhaps the most desirable classification. The hills at the former place influence so much their force and direction, that it is often very difficult to determine precisely the point whence the great atmospheric current comes; it is not always that there are clouds by which to determine, besides, when these are high, it not unfrequently happens that they are subjected to the movements of the higher currents, and passing away in a direction quite opposite to the wind below. On these accounts we shall denominate all those winds blowing from the south of east and west, vapour winds, and those blowing from the north of these points, dry winds,

The mean temperature of the vapour winds during the summer, is, in London, 66.8, and in Malvern, 62.4,° The mean temperature of the dry, during the same season, is, in London, 64.2, and in Malvern, 60. In the autumn the mean temperature of the vapour winds, is, in London 53.4, in Malvern, 53.6. The mean temperature of the dry, during the same season, is, in London, 49.4,° in Malvern, 47° So that the southerly winds in autumn at Malvern are rather warmer than in London.

The mean temperature of a climate, is generally regarded as made up of the average impression of the sun due to its latitude upon the surface of the globe. But in considering the climate of any place in Great Britain, this statement must be taken with some limitation; according to it, the cloudy days would always be the coldest, but during the winter season in this country, it is not generally so; on the contrary, the south west winds bring up large and copious accessions of vapour of a high constituent temperature, warming the air, and raising the thermometer; at the same time thick clouds form, and everywhere obscure the sky, accompanied very often with large quantities of rain; on the other hand, with northeasterly winds, the atmosphere is frequently freed from cloud, the sun shines brilliantly for days together, but the temperature in the shade is many degrees below the cloudy, damp, and vapourous breeze from the south-west. During the winter we have very frequently observed the maximum of the thermometer at eleven or twelve at night, or even one or two in the morning, a result that can only be due to a change of wind, and the consequent accession of warm vapour. In a clear sky, during the winter, the earth radiates heat, even in the middle of the day, almost as fast as it receives it, so that the temperature, in the shade, during a bright day at this season, advances but little; but warm vapour and dense clouds not only prevent the earth's radiating its heat, but bring with them a positive warmth.

The following circumstances must not be overlooked with reference to the climate of this country, for they have a most important influence. On the north is the Arctic Ocean, with its icebergs; on the north-east the frozen shores of Lapland, and the intensely cold mountainous regions of Sweden and Norway; on the east, the vast continent of Europe; on the south, the Atlantic, and the western shores of Europe; on the south-west, the ocean only; and on the west and north-west, the continent of America, and the North Atlantic.

It is a general fact that winds blowing over large tracts of land

The

are considerably colder than those blowing over the ocean. reasons for this it is hardly necessary for us to explain here, but the consequence is that N. E. winds are the coldest, S. W. the warmest ; N. W. are intermediate, with a northerly character; the S. E. intermediate, with a southerly character.

From these considerations, therefore, the winds are more accurately divided in the following diagram.

The dew-point can never be higher than the temperature of the air. Supposing, therefore, during the winter in the high regions of Lapland, Sweden, and Norway, the temperature of a breeze to be 20° or 24° F., often doubtless very much lower, air of that temperature cannot hold vapour higher than 20° or 24. This atmosphere being put in motion, and rushing rapidly to the southern and warmer regions, is constantly acquiring a higher temperature, but passing over only a limited track of ocean, it acquires but little increase in its vapour; the dew-point, consequently, remains very nearly the same.

Let us suppose that such a breeze has reached the temperature of 32° or 34° when arriving at the British Isles, the difference between this and the dew-point (20° or 24°) would constitute a very dry harsh wind, little likely to be accompanied with any deposition; on the contrary, drying up all the moisture it meets with, it would have precisely the character of our N. E. winds in a very marked degree.

On the other hand, a S. W. breeze coming from the warmer regions and over an immense tract of ocean, into the colder temperature of Britain, would soon become cooled, until the temperature of the air was no greater than the temperature of the vapour it bears with it or the dew-point. At this point, and pursuing still its northerly course, some of the vapour must be precipitated, or take the shape of cloud, in either of which cases it parts with that portion of its temperature which was necessary to its invisible May, 1835. Vol. II, NO. X.

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