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Swiss professor, Ed. Brückner.36 Taking all available observations of temperature, rainfall, and height of water in lakes and rivers since 1700, he has proved that, excepting such peculiarly situated regions as the West of England, the rainfall and the wetness of the seasons in Europe have, as a rule, their maxima and their minima at regular intervals of about thirty-five years. At the present time we are in a warm period of decreasing rainfall—the last maximum having been attained in the years 1882-86.37 Of course, rain is the most difficult part of weather to foretell, there being not two stations in this country where the rain curves for many years would be quite similar; but, all taken, we are now in a period of increasing dryness. Besides, Brückner suspects also the existence of a longer period, of over 100 years, which necessarily would interfere with the thirty-five years' period.
The moon has always been a favourite with weather prophets, who generally accuse meteorologists of a wilful neglect of the influence exercised by our satellite upon weather. The reality is, however, that meteorologists simply want to know what its effect exactly is, and that they failed for a long time to discover it. However, the recent researches of Bouquet de la Grye,38 A. Poincaré and GarrigouLagrange 39 show that if the effects of the moon upon our atmosphere are treated separately for the periods when our satellite is on the north of the equator and on the south of it they appear quite distinctly. If we take, for instance, the differences of atmospheric pressure in the latitudes 30° N. and 70° N., we find that they are notably greater when the moon is to the north of the equator. Masses of air must consequently be transferred from the lower latitudes to the higher ones, and such a transfer necessarily influences the distribution of winds.40
A number of other periodicities of weather is also under consideration. Such are the 19 years' period so forcibly advocated by H. C. Russel for Australia, and corresponding to the well-known period of 235 lunar months; the seven years' period discovered in America by Murphy, and three shorter periods of 424, 412, and 11:9 indicated by Lamprecht; the 267 days' periodicity in pressure and temperature noticed by Professor Bigelow, which would correspond to the period of rotation of the sun ; the 51 days' period detected at the Blue Hill Observatory; and so on. And finally there are the cold waves spreading every year in May, and the no less than six cold and three warm periods recurring every year in Europe, and indicated years ago by the veteran Scotch meteorologist, Mr. Buchan.
36 Klimaschwankungen seit 1700,’ in Pencki3 Geographische Abhandlungen, iv. 2, Wien, 1890. It was already mentioned in these pages (Nineteenth Century, January 1894).
37 A, McDowall, in Nature, vol. lix. 1898, p. 175, has given a very nice diagram to show it.
38 Annualre du Bureau des Longitudes, 1895; Meteorologische Zeitung, vols. xxviii. and xxx.
39 Comptes Rendus, vol. cxx. 1895, p. 844 ; cxxi. p. 468 &c.; cxxii. 1896, p. 846 ; cxxiii. p. 850.
10 See also Lindeman in Das TV'etter, vol. xiii. 1896, p. 145.
At every step we thus find in our atmosphere a recurrence of waves, large and small, and of fluctuations accomplished within periods of short and long duration. That many such waves must exist there is not the slightest doubt, and when all forthcoming evidence has been properly threshed, the knowledge of these waves will certainly be very helpful for the long-period weather forecasts.
The other direction in which research goes on, and in which most valuable knowledge has already been gained for the forecasts several days ahead, is the study of the different types of weather, inaugurated by Abercromby and van Bebber, the Indian and the American meteorologists."
The first long-period forecasts were made in India, on the basis of a few empirical sequences suggested by Henry F. Blanford. The whole life of India depends upon the timely beginning of the rainy season, its perseverance and its timely end. Consequently, it was a vital question to be able to foretell the coming and the general character of the monsoon which brings rains with it. This was begun by H. F. Blanford, and in the hands of his successor, Mr. Eliot, the seasonal forecasts, which are now issued semi-annually, become every year more rational and trustworthy.43 In India, owing to its tropical position, the seasonal changes of weather, which depend upon the general circulation of the atmosphere, are far more important than the irregular non-periodical changes upon which weather depends in Europe ; and this circumstance facilitates the task of the forecaster. Still it took years of study before the various causes influencing the monsoons became known ; but now the Indian meteorologists can foretell, as a rule, in the first week of June when the rainy southwest monsoon is expected to come, what will be its probable strength and general character, and what is the probability of that break in the rains in July and August which is so important for the crops. They also foretell the general character of the winter monsoon, but they find it difficult to prophesy when the rainy season will come to
41 The excellent little book of Ralph Abercromby, Weather: a Popular Exposition of the Nature of Weather Changes from Day to Day (International Scientific Series), of which the first edition appeared in 1888 and a third edition in 1892, ought to be in the bands of every meteorologist and observer of weather. Professor W. van Bebber's Die Wetterrorhersage, 2nd edition, Stuttgart, 1898, is also written in a popular style, and is also an excellent guide for weather forecasts: it ought to be translated into English.
42 A Practical Guide to the Climates and Weather of India, Ceylon, and Burmah, and the Storms of the Indian Scas.' London, 1889.
4 Douglas Archibald in Nature, vol. lv. 1896, p. 85; Quarterly Journal of the Meteorological Society, January 1896, quoted in the above. VOL. XLV-No. 265
an end, although its early termination, being fatal to some crops, may result in a famine.
In the temperate zone, where weather is much more governed by the conflicts between the great equatorial and polar currents of air than by the steady flow of these currents themselves, no such forecasts could be issued. And yet, under certain special conditionsnamely, in the Pacific North-West of Northern America—a rather successful attempt in this direction has lately been made by Mr. Pague, the forecast official at Portland, in Oregon. His predictions are issued in the spring for the coming summer, and in the autumn for the coming winter; not at settled dates, but as soon as the summer or the winter type of weather definitely sets in. Last year the summer type of weather made its first appearance very late in the season--namely, on the 7th of July—and it was only at that date that the summer forecast was issued. A steady dry weather and a succession of repeated short cycles of cool and hot days, with sprinkles of rain at the time of the changes, and occasional thunderstorms following the hot days, were predicted quite successfully.“
In the maritime portions of the temperate zone, and especially in Europe, weather prediction becomes a still more complicated problem. Even if we had regular observations, all the year round, of the surface temperatures of the Gulf Stream and the North Sea, we could only gather some broad hints as to the aspects of the coming seasons. However, even under such difficulties the genius of man finds an outcome. A careful study of thousands of weather charts has enabled Abercromby and Bebber to discriminate in Europe five distinct types and five sub-types of weather which have the tendency to prevail at certain seasons, to be maintained for several days in succession, and to be followed, each of them, by some other type of weather in preference to all others. Taking as an instance the type which Abercromhy described as the western type of weather,' if the forecaster sees it coming he is enabled to foretell with great probability that for the next three or four days there will be an elongated region of high pressure stretching from the West Indies to Vienna, with rapidly decreasing pressures towards the north. Broken weather-cool in summer and warm in winter-will be the consequence. Then-supposing we are in summer—when a change
" Monthly Weather Review, June 1898.
45 Very interesting researches have been made in this direction by Otto Petterson, who has shown the close connection between the surface temperatures of the Atlantic Ocean and the North Sea and the distribution of the daily isobars. (*Ueber die Beziehung zwischen hydrographischen und meteorologischen Phänomenen, in Meteorologische Zeitschrift, xiii. 1896, p. 285.) They have been continued with a decided success on the Gulf Stream by Dr. W. Meinardus, who shows that the surface temperatures of the Gulf Stream at the coasts of Norway in early winter are an indication as to the temperatures which will prevail in late winter and early spring in middle Europe (Naturrissenschaftliche Rundschau, xii. 1897, p. 106, and xiii. 1898, p. 209).
of weather comes there will again be a great probability of the central type of Bebber following the western. That means that all over Europe the pressure will be high during the next four or five days, attaining its maximum in middle Germany: from that region winds will blow outwards with great regularity, a blue sky will shine, there will be little rain, and the temperature, low in the mornings, will be above the average in the afternoons.
Of course all these are mere probabilities; but nevertheless the advantage of knowing these types of weather and their probable sequences is manifest.
is manifest. When one type has set in it lasts for a few days; if it has been broken for a day or two, and has returned, it will persist only the longer after the break; and the coming changes and their direction may be foreseen a few days in advance, if account be taken of the above-mentioned periodicities, and especially if the movements in the higher strata of the atmosphere have been taken notice of by means of cloud observations or of balloons and kites. In fact, some modest attempts at forecasting weather a few days ahead are already made, and we find them, in the shape of hints, at the end of the daily meteorological summaries of weather.
To make these previsions more secure, one thing is, however, of first necessity. It is the knowledge of how the great circulation of the atmosphere goes on at a given moment, and this knowledge can only be gained by regularly exploring the higher strata of the atmosphere. A beginning of this is being made by means of the meteorological stations that are planted in every civilised country of the world on the tops of some mountains by means of cloud observations, of international balloon ascents carried out at regular intervals, and especially by means of kites provided with meteorological instruments, which have lately been brought to a very high degree of perfection in America at the Blue Hill Observatory. But these high-level investigations are so full of interesting and instructive results that they must be analysed separately.
THE VIENELIK MYTH
The experiences related in these pages were gathered in two expedi-
The primary law which governs the Abyssinian is the physical configuration of his country. Ethiopia is an assemblage of high plateaux, rising 3,000 feet or more above the surrounding plains ; its