Page:Transactions of the Provincial Medical and Surgical Association, volume 4.djvu/203

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I have, on three occasions, tried the temperature of a very line and copious spring in the village, and the following are the results:—In the first, the temperature of the air was 30°, the water 50°; in the second, the air 56°, a thermometer immersed to the bottom of the spring 50.5°; in the third, the temperature of the air 7 5°, the water 52°—this was after ten days very hot and dry weather.

2. Atmospheric Pressure.—In instituting a comparison between two barometers, in order to estimate the atmospheric pressure at two distant places, it

and minima by Mr. Daniell, from observations for three years, is 49.5°; which corresponds, even to the decimal place, with Mr. Howard's estimate. The higher mean denoted by the above results, arises, probably, from the greater mildness of the winter of 1834-35.

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 be the coldest, but, during the winter season in this country, it is not generally so; on the contrary, the south-west winds, during the winter months, 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 north-easterly 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 vaporous breeze from the south-west. During the winter, I 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, at this season, bring with them a positive warmth.