462 POPULAR SCIENCE MONTHLY. 



interior, may easily give the impression of a changing climate. Even 

 in cases where individuals have kept a record of thermometer readings 

 during a long series of years, and are sure that the temperatures are 

 not as low or as high as they used to be, or who are convinced that the 

 rainfall is lighter or heavier than it was some years before, the chances 

 are that the location of the thermometer or the exposure of the rain 

 gauge has been changed sufficiently to account for any observed differ- 

 ence in the readings. 



Value of Evidence concerning Changes of Climate. — The body of 

 facts which has been adduced as evidence of progressive changes of 

 climate within historical times is not yet sufficiently large and complete 

 to warrant any general correlation and study of these facts as a whole, 

 especially from the point of view of possible causation. But there are 

 certain considerations which should be borne in mind in dealing with 

 this evidence, certain corrections, so to speak, which should be made 

 for possible controls other than climatic, before conclusions are reached 

 in favor of climatic changes. In the first place, it has been noted above 

 that changes in the distribution of certain fruits and cereals, and in the 

 dates of the harvest, have often been accepted as undoubted evidence of 

 changes in climate. Such a conclusion is by no means inevitable, for 

 it can easily be shown that many changes in the districts of cultiva- 

 tion of various crops naturally result from the fact that grapes, or corn, 

 or olives are in time found to be more profitably grown, or more easily 

 prepared for market in another locality. Thus the area covered by 

 vineyards in northern Europe has been very much restricted in the last 

 few hundred years, because grapes can be grown better and cheaper 

 farther south. Cultivation in one district is abandoned when it is 

 more profitable to import the product from another. It is easy, but not 

 right, to conclude that the climate of the districts first used has 

 changed. Wheat was formerly more generally cultivated far north in 

 the British Isles than is the case at present, because it paid. Later, 

 after a readjustment of the taxes on breadstuff's, it was no longer profit- 

 able to grow cereals in that region, and the area thus cultivated dim- 

 inished. Changes in the facility or in the cost of importation of certain 

 articles of food from a distance are speedily followed by changes in the 

 districts over which these same crops are grown. Similarly, the intro- 

 duction of some new plant, better suited to the local soil and climate, 

 will result in the replacement of the older product by the newer. In 

 France, Angot has made a careful compilation of the dates of the 

 vintage from the fourteenth century down to the present time, and finds 

 no support for the view so commonly held there that the climate has 

 changed for the worse. The dates of the vintage do, however, indicate 

 some oscillation of the climatic elements. In the period 1775-1875, 

 the average date of the grape harvest in Aubonne was about ten days 



