cumulative and irreversible. The first is a very old story. The formation of "loess" which forms the soil of steppes is part of its work. One of the most remarkable formations associated with glacial deposits consists of vast sheets of the fine-grained, yellowish, wind-blown material called loess. Somewhat peculiar climatic conditions evidently prevailed when it was formed. At present similar deposits are being laid down only near the leeward margin of great deserts. The famous loess deposits of China in the lee of the Desert of Gobi are examples. During the Pleistocene period, however, loess accumulated in a broad zone along the margin of the ice-sheet at its maximum extent. In the Old World it extended from France across Germany and through the Black Earth region of Russia into Siberia. In the New World a still larger area is loess-covered. In the Mississippi Valley, tens of thousands of square miles are mantled by a layer exceeding twenty feet in thickness and in many places approaching a hundred feet. Neither the North American nor the European deposits are associated with a desert. Indeed, loess is lacking in the western and drier parts of the great plains and is best developed in the well-watered states of Iowa, Illinois, and Missouri. Part of the loess overlies the non-glacial materials of the great central plain, but the northern portions overlie the drift deposits of the first three glaciations. (Ellsworth Huntington and S. S. Visher, Climatic Changes, their nature and causes, p. 155.) Both loess and sand must be subject to similar meteorological laws because both are wind-blown deposits. Geologists will no doubt wish to draw a distinction between them, but it is not their difference but their similarity which is of importance in meteorology. In The Times of November 1, 1923, is a description of the discovery of the nest and eggs of a dinosaur as well as the skeleton of the dinosaur herself suddenly overwhelmed by blown sand, at an epoch estimated as being ten million years ago, as completely and surely as the Psylli and the Persians of Herodotus' story1, and sand has been presumably accumulating in the Eurasian continent during the interval which has elapsed since that event. In general soil is accumulating in places where it can rest, ground-floors are gradually becoming basements, Roman causeways in Britain made to be walked upon as ground-floors, seventeen or eighteen hundred years ago, are now eight feet below the surface in St Albans and eighteen to twenty feet below in London. The Royal City of Jerusalem is some forty feet below the present ground-level. The importance of the gradual accumulations of blown sand was noticed briefly by Mascart in a communication printed in the Hann Band of the Meteorologische Zeitschrift. The formation of sand goes on at a steady rate and its gradual increase over cultivated areas is inevitable because there is no means effectively available for its removal by any natural process. Sand may be converted into cultivable soil by the admixture of other suitable ingredients as in Egypt by the periodic mixture of the mud of the Nile: but if the rate of increase of sand is greater than the corresponding supply of the other ingredients which human activity can provide, progressive deterioration of the soil, encroachment upon the rivers and their ultimate submergence, 1 See p. 70. are inevitable. Human agency can prevail against the gradual encroachment of sand for a time; but if the process is continued, any relaxation of effort means losing ground, and ultimately human agency is overcome and cultivation becomes hopeless, irrespective of any change of climate. Under existing geological conditions the process is irreversible. Soil In like manner the gradual removal of soil from the higher levels by the natural alternations in the flow of water due to heavy rain-storms, which are characteristic of the coastal climate of the Mediterranean, seems equally inevitable and irreversible. The soil of the uplands may be regarded as a strictly limited deposit of capital left by the preceding ice-age and the moist conditions which would follow it. Soil may accumulate locally by the action of vegetable growth; but on balance there must be less at the end of an ordinary year than at the beginning. As one passes through the high upland valleys of Europe one cannot fail to note the patches of cultivable soil, very limited in extent, that will serve to support a certain number of persons and no more. Assiduous labour might conserve the soil, but once washed away it can never be replaced. The process is irreversible and in course of time the population must migrate. These aspects of the inevitable course of natural history have to be considered before we appeal to the third process, the alternative which the advocates of a change of climate uphold, a change in the course or character of the general circulation of the atmosphere. CONCLUSION Hence we may conclude that in spite of modifications of the atmospheric circulation which have resulted in diminished rainfall and consequently had great effects from time to time upon civilisation in the Mediterranean regions, the general features of the circulation of air over the region from 22° N to 52° N have not changed and the sketch of the climate which we gave in chapter II, with modifications in normal values, may be taken as expressing the relative characteristics of the circulation known to the ancients, the seasons are the same and the crops are still mainly the same and require the same cycle of seasons, though the area over which they can be profitably cultivated may have been considerably reduced and some of the region may have been transformed from habitable land into inhospitable desert. We have still a similar circulation. The circulation is conditioned by a distribution of temperature over sea and land, and that in its turn by the energy received from the sun on the one hand and radiated into space on the other, and by the distribution of land and water. None of these can be pronounced invariable, but at the moment the quantitative evidence of change is of the nature of minor fluctuations rather than of sweeping modifications. These things have to be considered and in our ignorance of the realities of the atmospheric circulation we have indeed hardly begun to think with real lucidity about the physical causes of local changes of climate on the earth's surface. The 25 inches of snow in Jerusalem in February 1920 may possibly point the way to views which deserve consideration. If so great a fall of snow could occur at one time it could certainly be repeated if the conditions were favourable, and sufficient repetition would mean a change of climate for the whole of Eastern Syria. The winter gales and rains of the Mediterranean region are doubtless due to invasions of cold air coming from the highlands of Central Asia and finding its way to the shores of the Mediterranean East or West as mistral, tramontana or bora1. A little additional coldness of the Asiatic highlands would stimulate the circulation. We have already seen that the distribution of pressure in the winter is a long trough of low pressure over the sea between the vast continental high pressure with its cold winds from the East and the vast oceanic high pressure with its warm winds from the West. The play between the two keeps the balance with a succession of rainy depressions between them. If the continental high pressure should be exaggerated or the oceanic pressure enfeebled the trough would be pushed Southward and the influence of the cold enhanced. A little less cloudiness in winter in the Central Asian region might make all the difference between an adequate and an inadequate rainfall in Eastern Syria. What regulates the cloudiness of the highlands of Asia we have still to discover it is by no means an insoluble problem. It is simplified by the fact that only the winter conditions need be scrutinised, the summer months are rainless even in well-watered Mediterranean countries. Having completed our survey of the intricacies of the problem of the change of climate we may return almost to the starting-point by pointing out that the ancients themselves had views similar to those of modern investigators, and in support of that view we cite a quotation from Plato's Critias to which attention has been called by Dr E. G. Mariolopoulos, of the National Observatory of Athens2, in a paper which after full consideration pronounces against any notable change within historic times. The consequence is, that, in comparison of what then was, there are remaining only the bones of the wasted body, as they may be called, discernible in small islands; all the richer and softer parts of the soil having fallen away, and the mere skeleton of the land being left. But in former days, and in the primitive state of the country, what are now mountains were only regarded as high hills; and the plains, as they are termed by us, of Phelleus were full of rich earth, and there was abundance of wood in the mountains. Of this last the traces still remain, for although some of the mountains now only afford sustenance to bees, not so very long ago there were to be seen roofs of timber cut from trees growing there, which were of a size sufficient to cover the largest houses; and there were many other high trees, bearing fruit and abundance of food for cattle. Moreover, the land enjoyed rain from heaven year by year, not as now losing the water which flows off the bare earth into the sea, but, having an 1 E. G. Mariolopoulos, 'Sur la formation des dépressions locales méditerranéennes et la théorie norvégienne du "polar front,' Comptes rendus, Tome CLXXVII, 1923, pp. 597–600. 2 Étude sur le Climat de la Grèce, Les Presses Universitaires de France, Paris, 1925. abundance in all places, and receiving and treasuring up in the close clay soil the streams which descended from the heights, it let them off into the hollows, providing everywhere abundant fountains and rivers, of which there may still be observed indications in ancient sacred places, where fountains once existed; and this proves the truth of what I am saying. Such was the natural state of the country, which was cultivated, as we may well believe, by true husbandmen, who did the work of husbandmen, and were lovers of honour, and of a noble nature, and had a soil the best in the world, and abundance of water, and in the heaven above an excellently tempered climate. (The Dialogues of Plato, translated into English with analyses and introductions by B. Jowett, M.A., vol. III, Critias, p. 691, 2nd ed. Oxford, Clarendon Press, 1875.) While these pages are passing through the press we learn of a new discovery that supports the hypothesis of a definite and permanent change of climate within the last five hundred years in the case of Greenland. Recent excavations near Cape Farewell, described by William Hovgaard in the Geographical Review for October, 1925, throw light on the fate of one at least of the early Norse colonies in Greenland....The colony referred to is the "Eastern settlement," just west of Cape Farewell, and the interesting finds come from the cemetery, where they have been preserved by being permanently frozen into the ground, a condition which must have persisted for at least five hundred years. When the bodies were buried, however, the soil must have thawed, at least at midsummer. The costumes and many of the coffins, even the deepest-lying, are pierced and matted by the roots of plants, which would not have happened if the ground was permanently frozen. (Meteorological Magazine, vol. LXI, February, 1926, p. 13.) Greenland was discovered by Norsemen in 982 and flourishing colonies were established. But in 1400 trade with Europe had virtually ceased. In these circumstances, which included the change of climate, the colonists were overcome by the Eskimos; the new excavations disclose "the last Norseman... lying dead and unburied by his desolate and deserted dwelling, and holding in his hand the emblem of the cultural superiority of the European, the iron knife, which had been ground and ground to the verge of possibility." The reader will not fail to remark that, in these discussions, the changes of climate which are noted are mostly for the worse. The implications of that view are rather depressing. Aristotle however seems to have taken the more cheerful attitude that deterioration in one locality may be accompanied by improvement in others. CHAPTER VII FROM ARISTOTLE TO THE INVENTION OF THE BAROMETER: WEATHER-LORE, ASTROLOGY AND ALMANACS The hollow winds begin to blow, Sits wiping o'er her whiskered jaws. Quits mutton bones on grass to feast. GREEK WEATHER-LORE THE physical and dynamical theories of Aristotle's Meteorologica found little application as practical meteorology. The physical processes of the atmosphere were not effectively explained. The conflict between religion and science which had been the subject of Aristophanes' humour was still unsettled after the four centuries of experience of weather that lie between Aristophanes and Horace. Parcus deorum cultor et infrequens, consultus erro, nunc retrorsum plerumque, per purum tonantes (Horace, Odes, Liber 1, Carmen XXXIV.) The crucial case of lightning out of a clear sky propounded by the jestful personation of Socrates had in the experience of Horace gone against the philosopher. Even in the early days the philosopher was commonly regarded as having got out of his depth in his explanation of nature. The Greeks coined a special word μeтewpoλéo xns for a babbler about things sublime. Meanwhile the poets and philosophers concurred in dealing with the weather |