Western Asia, which extended, though in a modified degree, into Northern and Eastern Europe, while at the same time the pressure was low over the rest of Europe and in the north of Africa. At Tobolsk the mean pressure at 32° and sealevel was 30.685 inches, being fully an inch higher than that of Western Europe. On one day it rose at Tobolsk above 31 inches. Now it was by the enormous drawing force which the widespread low pressure prevailing over Europe called into play, that the cold, dry, heavy air of Russia and Siberia was drawn over Great Britain and other parts of the Continent. The arrows show a continuous stream of this air flowing from Tobolsk westwards through Russia, crossing the Scandinavian peninsula, and descending over Scotland as a northerly wind. At the same time the surface of Scotland was under a thick covering of snow; and the differences of pressure being at the time comparatively small, light winds and calms prevailed. This desiccated air permitted the pro cess of terrestrial radiation to proceed almost unimpeded; the thick covering of snow (which is a bad conductor of heat) checked the descent of the cold downwards into the soil, and the calm state of the atmosphere to a great extent prevented its diffusion upwards through the air. Hence almost all the cold of radiation was permitted to accumulate on the surface of the earth; and as the coldest air is the densest and the heaviest, the frost was severest in low-lying localities. On Christmas night the exposed thermometer fell at Carstairs, Lanarkshire, to -20°; the protected thermometer at Castle Newe, in Aberdeenshire, to -12°; and the mean temperature of the whole of the eastern slope of Scotland fell to 5°.5, being about 27° below the average. On the 24th, the highest temperature at Paisley was only 3°.5, and the lowest -5°.0, thus giving -0°.8 as the mean temperature of the day. It is doubtless under circumstances similar to these that great frosts have occurred, such as that experienced in Flanders in 1544, when, according to Mézerai, wine froze in the casks, and was cut by hatchets, and sold by the pound weight. When the causes conspiring to bring about frosts so intense as that of Christmas 1860 are considered,―viz., an extraordinary distribution of pressure similar to that exhibited in fig. 20, causing a stream of desiccated air to pass over Great Britain; the surface of the ground covered with snow; and the atmosphere calm, or nearly so,-it is easy to see why great frosts so rarely occur in the British Islands. 287. In Scotland, the barometer continued to fall with the falling temperature till the 25th, which was nearly the period of greatest cold, after which it rose steadily with the temperature and with westerly winds until the 28th. According to the rule usually given in books, this was in both respects anomalous, since we are thereby taught to expect a rising barometer with cold easterly winds, and a falling barometer with warm westerly winds. The exception shows the arbitrary character of the rule. Fig. 20 not only gives an intelligible explanation of this great cold, but it points out the proper method of inquiry into the causes of weather-changes. This great frost could not, it is evident, have been satisfactorily explained by observations limited to the British Islands and parts of the Continent adjoining, or even by observations from all Europe, excluding Russia; but the extension of the field of observation so as to embrace Russia, Western Asia, and Northern Africa, was necessary in order to arrive at the explanation. 288. The importance of these investigations is immensely enhanced when we consider the intimate relation which subsists between the march of temperature and the death-rate. This great cold increased the death-rate to a fearful extent; indeed, more deaths were occasioned by it than happens when cholera or any other pestilence stalks over the land. With a more extended field for our daily weather-telegrams, the notification of the approach and continuance of weather so disastrous to the weak might be shown to be possible; and if so, the physician could then take measures in time to secure for his patients, who might require it, an artificial atmosphere of warmer and moister air, and thus extend the sphere of his usefulness in assuaging suffering and prolonging life. 289. Example 8.-The Cold Weather of July 1867.— This month was particularly cold and ungenial, but it was from the 18th July to the 1st August that the temperature was most deficient. The following figures indicate in inches the mean pressure during these two weeks :-Iceland, 29.928; Farö, 29.906; Shetland, 29.816; Orkney, 29.892; Hebrides, 29.896; Ross-shire, 29.868; Aberdeen, 29.825; Islay, 29.850; Liverpool, 29.831; Haddingtonshire, 29.821; Jersey, 29.882; Paris, 29.941; Vienna, 29.950; Brussels, 29.849; Riga, 29.658; St Petersburg, 29.670; Stockholm, 29.607; Mandal, south of Norway, 29.570; Christiania, 29.532; Hernösand, 29.552; Haparanda, 29.595; Vardo, north of Norway, 29.725. The pressure being low in Norway and countries surrounding the Baltic, and high in Iceland, Scotland was thus placed in the cold arctic current which set in from Iceland towards the Baltic. A comparison of the above pressures 59 with the mean pressure for July, of this part of the earth's surface (Plate I.), will show how completely the usual summer pressure in Scotland was reversed at the time, in consequence of which cold northerly winds (N.E., N., N.W.) took the place of the warm breezes from the south. The influence of this anomalous distribution of the pressure on the temperature is graphically exhibited in the two accompanying charts of the British Islands. The mean July temperature, fig. 21, is what occurs when the pressure is the average as in Plate I. Fig. 22 shows the mean pressure which occurred from 19th July to 1st August 1867, when the pressure was as detailed above. At Muthill, Perthshire, the mean temperature from the 22d to the 26th was only 48°.0, being 10° below the average, and during these five days the temperature did not rise above 54°.0. On the 23d frost occurred at Sandwick which injured potatoes and dahlias growing in low-lying situations-an unusual occurrence at this season, particularly in Orkney. In Scotland, mist and fogs accompanied this period of low temperature, and as a consequence, the deficiency of temperature was greatest during the day. 290. Hence its disastrous effects on the harvest. It has been proved that in Scotland a temperature of at least 56°, with the average amount of sunshine, is required to ripen wheat and barley properly. But during this period the temperature was far below 56°, and the sunshine was at the same time very deficient; and hence, though the temperature sufficed for the growth of straw, it was altogether inadequate to carry on the functions which are concerned in maturing and ripening the kernel of the seeds, upon which the quality of the grain depends. Many of the wheat and barley flowers never ripened into seeds; and of those which ripened, the tough outer covering of the seed, usually thin, was large and abnormally developed, and the white kernel, usually large, was small and deteriorated. 291. It is evident from these remarks that, if we would understand aright the weather of Great Britain at any time, it is absolutely indispensable to have before us at least the barometric pressure, the temperature, and the winds, from at least the greater part of Europe. Another remark may be added. Though all meteorologists now agree in thinking that daily telegrams of the weather should not be attempted, yet a great deal not merely of negative information (such as the nonoccurrence of storms), but also of positive information regarding the suitableness of the coming weather for travelling, farming operations, the growth and ripening of the crops, and for other objects and purposes of human life, may be most certainly concluded from daily weather-telegrams received from a wide field of observation. There is another use to which daily weather-telegrams may be put. It will be evident, from these illustrations of the relations of the pressure and temperature of the atmosphere and of the winds, that daily observations, particularly barometric, from a number of well-selected points in Europe, would supply sufficient data |