No matter in what minor respects the curve may be changed by further investigation, one feature can scarcely be eradicated, namely the sinuosity. It appears impossible to interpret this in any way except as conclusive evidence of pulsations of climate extending over hundreds of years. Omitting the earlier and less certain parts of the curve, we see that at the time of Christ the average sequoia tree grew at least thirty per cent. faster than in 1500 A. D. This does not mean that the rainfall was exactly thirty per cent. greater. It may have been twice as great, but as to that we cannot yet speak with any certainty. Thus much, however, seems evident: if the huge sequoia trees high among the relatively moist mountains fell off thirty per cent. in their average growth in spite of their favorable position and vast root systems, smaller vegetation must have diminished to several times as great an extent. Moreover we are not dealing here with individual years, but with decades, which would appear to mean that individual years must have shown much greater extremes than those indicated in the curve. We infer then that during the last three thousand years not only has the climate in general become drier as indicated by the general trend of the curve, but that it has been characterized by pulsations lasting hundreds of years and by variations in rainfall sufficient at least to halve or double the productivity of the land.

Thus far we have been dealing with California, but our results appear to apply to Asia and Europe with equal force. For the sake of comparison I have added to the diagram a dotted line. This represents the condition of the curve of climatic pulsations in Asia so far as I had been able to obtain data up to 1910, the time of writing Palestine and its Transformation, from which volume (pages 327 and 403) the curve is reproduced. Since then a few further facts have been noted which would tend to modify the curve somewhat. As time goes on there can be no doubt that further modifications of considerable importance will be necessary. It must be borne in mind that this curve is a pioneer attempt at the elucidation of an extremely complex subject. At the very best it merely bears the same relation to the ultimate truth that the history of Babylonia and Assyria as written by Rawlinson bears to the history of those same countries as written in the light of the most recent excavations.

In spite, however, of the avowedly tentative nature of the Asiatic curve, it agrees to a notable degree with that of the trees of California. To be sure there are certain marked disagreements. These may be due to actual differences between the changes in California and Asia, or to an absence of data in compiling the Asiatic curve.

Among meteorologists and climatologists there is a growing conviction that a change of climate in one part of the world is synchronous with that in another. As Ward puts it in his authoritative work on Climate, "It is now believed that oscillations of climate are limited. in time, but occur over wide areas.' Therefore the presumption is that further knowledge of the climate of Asia will cause the curve for that portion of the world to be modified until it approximates to that of California. Nevertheless differences in latitude may cause a given climatic change to assume different aspects according to the zone of winds with which we are dealing; and there is some reason to think that oceanic areas are subject to changes more or less contrary to those of continents. The Californian curve comes from a small continental or interior region between 36° and 37° north of the equator. The Asiatic curve, on the other hand, is based on data from diverse continental regions located from 30° to 42° north of the equator, and is therefore more liable to error than is the other.

The degree of difficulty experienced in preparing the Asiatic curve may be judged from the fact that the line is straight between 1200 and 1000 B. C. simply because between those dates I have as yet been able to find no facts bearing directly upon the climatic conditions. Further data might have caused the curve to be sinuous in harmony with the American curve. In other cases the fact that marked evidences of aridity were noticeable at a particular time or happened to be recorded by man or nature with especial clearness may have led me to carry the Asiatic curve lower than was justifiable. For instance a marked degree of depopulation, an uncommonly low level of enclosed lakes, traditions of famine, and other evidences appear to indicate that the seventh century of our era was an exceptionally dry time, but there is absolutely no available evidence as to the exact time when the dryness culminated, nor as to how dry that particular century was as compared with others. A curve drawn as indicated by the dashes would have fitted the facts equally well. Even as the curves now stand, however, the longest continuous decline in the Californian curve culminates at the middle of the seventh century at about the time when the Asiatic curve is lowest. Another case of almost exactly the same kind is found in the thirteenth century. There are pronounced evidences of aridity in Asia at the end of the twelfth century and in the first half of the thirteenth. Therefore the curve dips very low, and the minimum. point is placed during the first part of the thirteenth century. The next available evidence indicates favorable conditions in the first R. DeC. Ward, Climate considered especially in Relation to Man, p. 363 (New York, 1908).

part of the fourteenth century. In the absence of any knowledge as to the latter half of the thirteenth century, the curve was originally drawn as shown in the dotted line. The Californian curve, however, fits the facts quite as well, and probably indicates the true state of affairs not only in America, but in the same latitudes in the eastern hemisphere. Similar reasoning applies to the low portion of the curve found at 300 A. D. At about that time a large number of ruins were abandoned in places which are now waterless, and other types of evidence also suggest aridity. Nevertheless it is probable that this and, to a less extent, the other main depressions of the Asiatic curve are exaggerated because special events happened to culminate at those particular times.

In spite of certain differences the high degree of agreement between these two curves from parts of the world as remote as western Asia and California is remarkable. Take the epoch centring at the time of Christ, for example, or those which centre at 1000 A. D. and 1600 A. D. The agreement is so close that it cannot be a matter of chance. This is the point which needs especial emphasis. We have here two curves based on entirely diverse kinds of evidence from parts of the world six thousand or more miles apart. One of the curves is based on lines of evidence which are at best highly fragmentary, and into which the element of personal interpretation enters largely. The other is based on a line of evidence which is absolutely continuous for two or three thousand years, and into which the element of personal judgment enters not at all. The two curves agree as to their main features, and in some cases the agree\ ment extends to small details. The only satisfactory explanation of this result seems to be, first, that the climate of many portions of the past was different from that of the present; secondly, that climatic pulsations having a periodicity of centuries have been the rule; and thirdly, that these pulsations have been essentially synchronous in the eastern and western hemispheres.

If these conclusions be granted, it at once becomes evident that the climatic pulsations must be taken into account in the interpretation of history. How important they are, however, cannot now be determined. To the geographer and especially to one who has devoted years to this particular line of study, they probably appear more important than they really are. Therefore I speak with diffidence, and only in the hope that duly qualified historians may find the matter of sufficient interest to warrant its independent investigation on their part. I shall merely try to point out some of the ways in which climatic pulsations may have exercised a certain

amount of influence upon some of the important events of history. I shall speak chiefly of the possible results of increasing rather than of decreasing aridity, partly because they are more manifest, and partly for lack of space. I shall assume, furthermore, that even where events in Asia are under discussion the climatic curve of California, based on the exact tree measurements, represents the truth more closely than does the largely inferential Asiatic curve. I realize that the considerations which I shall present may seem highly theoretical, but in the early stages of every great scientific problem nothing is so stimulative of thought as a theory to be attacked or defended. The theory, as stated on page 251 of Palestine and its Transformation, is as follows: "It seems to be true, as a principle, that, in the regions occupied by the ancient empires of Eurasia and northern Africa, unfavorable changes of climate have been the cause of depopulation, war, migration, the overthrow of dynasties, and the decay of civilization; while favorable changes have made it possible for nations to expand, grow strong, and develop the arts and sciences."

The first and most obvious effects of climatic changes are economic. At the present time countries like Greece and Asia Minor suffer grievously from the failure of crops every few years. There is no reason to think that there has been any distinct change of climate during the past century, and conditions are now probably better if anything than in the early part of the nineteenth century. Nevertheless distress and famine have prevailed more than once, and have been serious contributory causes toward political discontent. If a country like Greece were fully populated about 400 B. C. at the end of two centuries of increasingly favorable climatic conditions, a change such as that which appears to have taken place during the succeeding two hundred years might not cause famines, but it ould entail a constant pressure upon the means of subsistence. A highly developed people might thrive and prosper even in the face of growingly adverse conditions and might even be stimulated thereby to greater exertions. Nevertheless the constant pressure of diminishing crops would tend to drive people to emigrate and in the end it might have much to do with weakening them and preparing them for final conquest by outsiders. It would also gradually diminish their purchasing power so that trade would on the whole tend to decline or would seek new channels. The purchasing power of any nation depends ultimately upon the natural resources of the country, and in the case of practically all the nations of antiquity the resources were almost wholly agricultural. Thus a gradual diminution of the crops

would inevitably prevent the growth of trade with foreign countries, and would eventually tend to destroy it. Increasing rainfall would naturally produce the opposite results. To judge from the inscriptions and monuments, trade between Egypt and Mesopotamia was never brisker than in the seventh century before Christ when Assyria was at the height of its power. Again in the period of Rome's chief expansion, not far from the time of Christ, caravan traffic seems to have been carried on in the dry parts of Asia with a vigor far in excess of that which prevailed a few hundred years later. Other conditions may have had much to do with this, but a long succession of good crops could scarcely fail to produce a stimulating effect.

Another result of changes in rainfall and hence in agricultural prosperity would be the effect on the relation of the farming population to the government. If the scale of taxation were based on a period of prosperity, a change to worse conditions would inevitably cause friction. The governors would insist upon the payment of as heavy taxes as formerly; the farmers would declare themselves unable to pay so much. Then, as has happened frequently in Turkey during recent periods of drought, the officials and their minions. would make attempts to collect what they considered their due, and would employ force and extortion. Such practices would have the effect which we constantly see at the present time among the Kurds and Armenians. Those parts of the population which did not belong to the governing class would be embittered, and would be ready to listen to anyone who promised them better conditions. It seems probable that many civil commotions and many attempts of usurpers to gain dominion may have been rendered possible by the discontent into which prolonged periods of poor crops have thrown the populace. Here, as in so many cases, physical conditions alone might have little effect, but when combined with the necessary human quality, such as ambition on the part of some petty sovereign, they may have large results. If the people were thoroughly contented, the ambitions of the upstart might never have the opportunity to come to fruition.

Discontent due to prolonged poor crops tends to make people - unstable, not only politically but in other ways. Religious bitterness is almost sure to increase under such conditions. A portion of the community attributes its poverty to the fact that its own gods are not so strong as other gods, or that there is something wrong with the present form of religion. The rest of the community is inclined to attribute its distress to the wickedness of its neighbors who decry the old religion; and thus bitterness and persecution are apt to be