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from which really trustworthy conclusions could be drawn regarding the weather from day to day over any part of Europe in which for the time we might take an interest. And who is not so interested at the critical seasons in summer and early autumn, when the weather which then prevails over Europe really determines the state of the markets for the next year? If Mr Reuter would add to his daily telegrams a note of the weather, as suggested in par. 25, and if buyers and sellers would take the trouble to make a private note of these weather-telegrams from day to day, and gave a little attention to understand the principles of meteorology, they could not fail to arrive at a tolerably accurate estimate of the probable productiveness of the harvest in grain-producing countries. In this way they would be less in the power of the heartless spirit of speculation, which for its selfish ends too often succeeds by false representations in raising and depressing prices.
292. Some time ago I examined the mean temperature of Europe for each week of the year, beginning 1st April 1865, and ending 31st March 1866,* from observations made at sixtythree places as well distributed as possible over the Continent; and having calculated the excess or defect of each week's mean from the average of the week, constructed fifty-two charts, which exhibited by shadings of red and blue where and to what degree the heat and cold of each week was distributed. Among many points of interest which the charts brought into prominence, perhaps the most interesting was the relation between the pressure and the temperature of the atmosphere which they were found to illustrate in every case in which such relation was made the subject of examination. When a high pressure appeared in the N.E., N., or N.W., and pushed its way southwards or westwards over the Continent, its march was marked by a falling temperature, and the degree of the accompanying cold was generally proportioned to
* See Journal of Scottish Meteorological Society, New Series, Nos. ix. and xi.
the difference between the pressures in the N. as compared with the pressures in the S. On the other hand, when a high pressure emerged from the S. or S.W., and thence spread itself over Europe, a rising temperature followed in its train, generally proportioned to the extent and volume of the equatorial current. These waves of temperature and pressure were frequently so vast that the whole of Europe could exhibit no more at one time than what seemed to be the merest fragment of one of them.
293. INTERRUPTIONS OF TEMPERATURE.— It is well known that in no year does the temperature regularly increase till it reaches the maximum in July, and thence fall without interruption to the minimum in January. But it might be supposed, that if the mean temperature of each day of the year was deduced from a series of observations extending over many years, a close approximation, if not an absolute agreement, with such a regular increase and diminution would be arrived at. Now, the results of all observations hitherto made are unanimous in telling that this is not the case; but that, on the contrary, there are certain periods, more or less well defined, when the temperature instead of rising remains stationary, or retrogrades -instead of falling, stops in its downward course, or risesand at other times falls, or rises for a few days at an accelerated speed. These interruptions are noticed here because they illustrate the connection between the pressure and temperature of the atmosphere.
294. Some of these periods are to a certain extent publicly recognised, and have a place among the weather apophthegms current in different countries, thus evidencing the degree to which they obtrude themselves on public notice. One of the best marked of these periods occurs from about the 11th to the 14th of April, or about the beginning of April, Old Style. This is the cold weather commonly known as the BORROWING DAYS. In Scotland there are several rhymes descriptive of it, of which the oldest is evidently the following
“ March borrows frae April
Three days, and they are ill :
This is a capital description, giving by a few simple but strong touches the principal features of one of the bitter “norlan' blasts” or storms of the spring equinox; and it is all the more accurate inasmuch as these interruptions of temperature are more or less connected with storms.
A period of cold weather also occurs in the middle of May. This cold is very extensively distributed, as is shown not only by its appearance in meteorological records, but also from its prominent position among the “weather saws" of every country in Europe. *
295. I have examined the temperature of Scotland for a number of years, and have shown t that the following interruptions occur from year to year, with very rare exceptions, in the annual march of the Scottish temperature :
1. 7th to 10th February.
3. 9th to 14th May.
4. 29th June to 4th July.
1. 12th to 15th July.
3. 3d to 9th December.
296. The interruptions which take place in July, August, November, and December have been particularly examined ; but since the same conclusions have been arrived at for them all, it will be enough to state the results of the examination of the November and December interruptions. The cold
For an account of the cold week of May, see a paper of great elegance and learning read by Dr Arthur Mitchell at a meeting of the Scottish Meteorological Society, and since published in ‘Good Words,' May 1866.
+ Journal of Scottish Meteorological Society, Nos. xiii., xiv., and xvi.
weather in the beginning of November is accompanied by an unusual prevalence of N. and N. W. winds, and by calms; by a diminution of the amount of the invisible vapour of the atmosphere; an increase in the rainfall, both as regards amount and frequency ; and a more frequent occurrence of fogs. On the other hand, the mild weather of December is accompanied by an extraordinary predominance of southerly winds, and an almost total absence of northerly winds; an increase in the amount of the aqueous vapour, and a considerable increase in the rainfall, both in amount and frequency.
297. Hence, then, as regards the causes of the interruptions in the regular annual march of the temperature, we are led to one conclusion-viz., that they re determined and regulated by the wind. Nothing could present this in a clearer light than the winds which are found to occur during the November and December periods. Thus, during the cold period of November, winds from the N.E., N., and N.W. were in the proportion of 35 per cent, while winds from the S.E., S., and S.W. were 29 per cent. On the other hand, during the mild period of December, winds from the S.E., S., and S.W. were in the proportion of 69 per cent, while winds from the N.E., N., and N.W. were only 5
298. But since the wind is only an effect or consequence resulting from differences between the atmospheric pressure in Scotland and that of neighbouring regions, we must look to the atmospheric pressure for an explanation of the interruptions of temperature. The pressure was examined with this view, and it was found to hold universally during the cold periods that pressure was higher to the north of Scotland and lower to the south, thus drawing over Scotland the polar current, and thereby depressing the temperature ; and during the warm periods, that pressure was higher in Scotland than in places to the north, thus drawing over the country the warm stream of the equatorial current. Thus the unusually cold or warm periods which occur with considerable regularity at
certain times of the year have, so far as examined, been proved to depend on the relations of the polar and equatorial currents to each other. The circumstance that one of these great atmospheric currents, and not the other, prevails over this portion of the earth's surface at stated seasons is a valuable fact in meteorology, and the more so from the light it seems to cast on the periodicity of weatherchanges.
299. The commencement of each of these more anomalous periods is subject to variation from year to year; during the past fifty years some of them appeared every year between the dates specified, and none failed to make their appearance on more than five of the years. Being also of short duration, seldom exceeding six days, and most frequently limited to three or four days, they are sudden and striking—thus differing in character from a well-known anomaly which occurs in the latter end of January and earlier part of February. In regard to this anomaly Principal Forbes, in his paper “On the Climate of Edinburgh," remarks: “In most European instances it affects materially the mean temperature of February, which is very commonly far too high when contrasted with the general sweep of the annual curve. At Brussels, M. Quetelet finds an excess in the temperature of February above the general curve of at least 10.5. The same peculiarity may be noticed in the annual curves of London, Prague, St Petersburg, Vienna, and many other places, including the Great St Bernard.” It is probable that a careful examination of the monthly isobarometric curves will lead to a better knowledge of so important an anomaly, and of the causes of its occurrence when the region over which it spreads has been accurately defined.
300. From the principles enunciated it is plain that the climate of Scotland is ruled and determined by the relations which most commonly exist between its atmospheric pressure and the pressure of surrounding regions. Since the same principles are applicable to the whole atmosphere, it also follows that mean monthly isobarometric charts furnish us