Elsworth Huntington, of Yale, has investi gated the effects of weather and climate on the efficiency of several thousand factory workers in New England, Pittsburgh, North Carolina, Georgia and Flonda, covering a period of four years, and for one year of some 1,700 students at Annapolis and West Point. He found that in the performance of skilled labor or in intel lectual activity the greatest efficiency was neither in the coldest months nor in the warm est months; neither on the coldest days, nor the warmest days, but in the fall and spring, and on days of moderate temperature and considerable diurnal range. It appears that physical energy and mental acumen are least in mid-winter, and less in severely cold winters than in mild ones; that there is a second minimum of human energy in midsummer, which is less when the summers are abnormally hot than when they are cool. As his investigations proceeded southward he found the relation of efficiency to the seasons to gradually undergo a change, until in Florida the conditions were exactly reversed, the greatest efficiency occurring in winter and the least in summer. The long, warm, humid summers and the late spring and early fall were enervating, while the short winter, instead of being cold enough to be de yeting to the vital powers, was stimulating. he totality of human energy for the year was greater in the North than in the South.
It was found that people are physically most active when the average temperature of the day is 60° to 65°, that is, when the noon tem perature rises to about 70°. Mental activity reaches a maximum w.hen the average tempera ture for the day is 38°, that is, when there are mild frosts at night. People do not work so well when the temperature remains constant, nor do they when the changes are excessive. The ideal conditions are moderate changes at frequent intervals. With an average tempera ture of 65° to 70° a relative humidity of about 60 per cent is desirable. The relative humidity of places of habitation in winter is usually not over half the latter amount.
Change of For long it has been the opinion of meteorologists that there has been no change in climate during the penod of authentic history; that the vast changes that have occurred during geologic periods have been accomplished by slow mutations covering thousands of years before the accumulated changes were measurable and apparent. But evidence is now multiplying that these views will need to be modified. The records left by moraines, the changing shores of inland seas and the thickness of the annual rings of the sequoia trees, which live for several thousand years, strongly indicate that since the last glacial period, of which there have been at least sev eral, there have occurred climatic oscillations measurable by only a few thousand years and others whose span would come within one to several hundred years. Gradually geologists have unraveled the skein of glacial tracings and perceived that the ice periods consisted of at least four epochs separated by interglacial epochs, during which the climate became mild as at present, or even milder. Then evidence was found of other glacial periods farther back in geologic. time, also divided into epochs. In
certain regions vast sheets of ice spread south ward to the southern part of the temperate zone, while at other times tropical conditions existed as far north as Greenland. The record wrought by the last ice age shows that the melting of the ice sheet did not progress uni formly. Several times the melting ceased and the climate seemed to return to glacial condi tions, but the.se changes were minor in compari son to the great pulsations of climate that caused the vast ice sheets. There are other evidences that there have been changes of climate other than the slow mutation between glacial periods. A study of the abandoned strands of inland seas yields strong evidence that the waters did not fall regularly, but in irregular periods of wet and dry times which were meas ured by hundreds of years rather than by thou sands. Hunting-ton, whose valuable studies and researches have been long-continued and in many parts of the world, believes that during the past 20,000 or 30,000 years the climate of the earth has been subject to a great number of small changes, just as during the immense lapse of geological times it has been subject to a less though considerable number of great changes, each of which in turn seems to have been diversified by many minor variations. But this does not mean that there have been changes that are appreciable during the period of an in dividual life, as many believe 1,vho have not made a careful comparison of meteorological records.
Certain it is that the advance students of to-day are turning to the sun and studying variations in its radiations and other forrns of activities with the hope of solving the problems of changing climate and the initiation and continuance of storms. The writer agrees with those who believe that variations in the number and magnitude of sunspots, prominences and faculm are not the cause of vanations in terres trial weather and climate but are themselves the effects of the same solar cause that effects earth conditions.
Effect of Forests on is often said that the climate of a place depends largely upon the extent and proximity of vlooded areas; that the number of rainy days and the amount of rainfall are modified by change of forest extent and drouths and floods affected. It is certain that in some regions trees once grew more abundantly than at present. This however, should not be taken as proof that , destruction of the forests has resulted in a decrease of rainfall. The forests have dimin ished — in some cases wholly disappeared and it is also true that the precipitation is less; but this decrease of rainfall might better be regarded as the cause rather than as the result of the barren condition of the soil. There is no evidence that the forests were ever more extensive in Alaska and in other high altitude countries than they now are. Nevertheless, in these countries, just as in the arid regions of great continents, there is evidence of a long period climatic change—a decrease of pre cipitation or an increase of temperature, or both —. a change that cannot be due to defores tation.