RESULTS (5F COMPAKATIVE OBSERVATIONS: BAVARIA. 235 



companied by observations upon vegetable physiology and other sub- 

 jects closely related to climatic iufluences. 



Temperature of the air in the open fields and in icoodlands. 



The climate of a given country or locality depends, in the first place, 

 on the temperature of the air; and if we wish to learn the influence 

 which forests or clearings have upon the climatic conditions of any place, 

 comparative observations must be made in wooded and in cleared places 

 through a considerable time. The warmth of the air is communicated 

 from the sun, either by direct absorption of the solar rays, by reflection 

 from the warmed surface, or by radiation from the surface that has been 

 warmed. lUost of the warmth of the air is from the latter. The air 

 coming in contact with the warmed surface, expands and rises, to be 

 immediately replaced by cool air. The air in the forest is cooler, because 

 the sun's rays do not reach the soil directly. The atmosphere is there 

 warmed more from the earth than by the direct rays of the sun. 



The annual mean temperature of the air in the woods is somewhat 

 lower than in an unwootled space, but the influence is very small in the 

 yearly result. The annual mean temperature of the air in the forest 

 increases steadily from the surface of the earth to the tree-tops. 



But the annual mean temperature of a given locality affords but a very 

 uncertain knowledge of the climatic character of the place. A hot sum- 

 mer and a cold winter may have the same annual mean as a cold summer 

 and a mild winter. The distribution of the warmth of the air among 

 the seasons, especially in the spring and summer, is of more imj)ortance 

 to plant-life than the yearly warmth. 



In the spring the forest air, at the height of five feet, is generally cooler 

 than the air in the open fields. 



In summer (the principal season of growth), the differences of temper- 

 ature between the air of the forests and fields have been greater, at all 

 places of observation, showing the influence of woodlands, as well upon 

 the temperature of the air as upon the soil. The hotter the summer the 

 greater the effect upon both. The absolute influence of the woodlands 

 upon the soil is twice that which they have upon the air, as on the aver- 

 age, the air in the forest during the day was I0.68 (R.) colder than in 

 the open field, while in the mean temperature of the forest soil was 30.24 

 (R.) lower than in the open fields. These results show that in well- 

 wooded countries, in summer, the daily mean of the air, but more so of 

 the soil, juust be lower than in thinly-wooded regions. The clearing 

 of lands will, therefore, raise the temperature of both air and soil, and 

 cause increased evaporation and greater dryness. 



In autumn, the influence of forests decreases, both in the air and the 

 soil, and the difference of air-temperature in the day-time, in the general 

 average, is only 0.° -45 (E) less than in the open fields. 



In tcinter, the difl'erence is very small, the air in forests being slightly 

 colder than in the fields. This is at variance with the prevailing opin- 

 ion, that the woods are warmer in winter than the open country, and 



at stations, the 'work beiug entitled, Die gesammte Lehre der Waklsfreii, viit Buclcsiclit 

 aiif die chemische StaiiJc dea Waldbauea. Berlin (1868), pp. xii, 300, and 110. 



No results of forest meteorological observations have been X'ublished by this author 

 einco 1873, but as ten years of record will have been completed on the 1st of March, 

 1878, he then proposes to give the results of this period, using the accumulated mate- 

 rials in a fuller study of the climatic conditions of woodlands. Dr. E. informs us in 

 correspondence, that he is now engaged in the preparation of a work on the chemistry 

 and physiology of plants in their relation to sylvaculture and agriculture. A ten-year 

 series of phaenological observations (periodical phenomena of animal and vegetable 

 life) will also be completed in 1878, and the results will then he published. 



