Climate has been variously defined as the sum total of weather, average weather, typical weather, etc., but the conception is still somewhat indefinite. We know that, while the weather of any place is subject to incessant changes, its climate persists; but we need not assume that it persists indefinitely. The geological record proves, on the contrary, that vast changes of climate have occurred in the course of long ages. In Antarctica and in Spitzbergen are found deposits of coal, constituting the débris of ancient forests such as could not exist in the climates now prevailing in those regions. There are plenty of other proofs that great climatic changes have taken place from one geological period to another; but what of changes in shorter intervals of time? An immense amount of zeal and energy has been devoted to the study of supposed changes of climate. Evidence of such changes is sought, on the one hand, in a painstaking examination of weather records (a process often involving the tabulation of hundreds of thousands of figures), and, on the other, in the collection of geographical and historical data bearing on the question. There have been numerous reports of the gradual drying up of African and Asiatic lakes, of the discovery of ancient ruins indicating that prosperous agricultural communities once flourished in regions that are now deserts, and of various other tokens that marked vicissitudes of climate have occurred within historic times. A recent ingenious method of studying climatic variations is to measure the successive annual rings seen in cross sections of old trees. Thick rings are supposed to have been formed during periods of abundant rainfall, and thin rings when the rainfall was deficient. This method has been applied to the giant _Sequoias_ of California, some of which are more than 3,000 years old. The net result of a wide range of investigations appears to be that, on the whole, climate has everywhere been remarkably constant since the dawn of human history. There is much evidence that, in certain regions, there have been alternate increases and decreases--recurrent oscillations--of temperature, rainfall, etc., but there is little evidence of progressive changes in one direction. In contrast to the uncertainty that still prevails in the scientific world on the subject of climatic changes is the confidence with which the average layman may be heard to assert that such changes have taken place within his own recollection. The popular idea that climate has changed perceptibly within a single human lifetime is a world-wide delusion, and one that has, apparently, always flourished. In the United States we hear of the “old-fashioned winter,” with its unlimited sleighing, and also of a marked increase or falling off in the rainfall in certain districts. It is an interesting fact that a century and more ago Americans were indulging in the same sort of retrospections.