1 882.] Forests — their Influence upon Climate and Rainfall. 29 



drought, -which is of ultimate importance to the farmers' crops and 

 vegetation in general. It will be seen that all our deductions have 

 been drawn largely from the known facts from observations. 



The experiments of L. Fantiat and A. Sartiaux (Translation of 

 a communication to the French Academy of Sciences, Pop. Sci. 

 Monthly for June, 1875), which have come to the notice of the 

 writer since the above has been written, are of great value as well 

 as interest. Space is wanting to give at any length the experi- 

 ments of these authors. They say: " We now made the follow- 

 ing observations in the heart of the forest of Helatte, which em- 

 braces 5000 hectares of land. At the height of about six meters 

 (say twenty feet) above a group of oaks and hornbeans eight or 

 nine meters high, we placed a pluviometer, pscychrometer, maxi- 

 mum and minimum thermometers, and an evaporometer, so as to 

 ascertain at that point the amount of rainfall, the degree of satu- 

 ration of the air, and the rate of temperature and evaporation. 

 In open air at a distance of only 300 meters from the forest, and 

 at the same height above the ground as in the former case, we 

 placed similar instruments under the same conditions. With 

 regard to the rainfall and degree of saturation, the observations 

 for six months showed the total rainfall to be 192.50"'" 1 in the 

 forest and 177. mm in the open air, difference in favor of the forest, 

 I5.50 mm . The degree of humidity for the open air showed a 

 mean of 61.7, and in the forest 63 , difference in favor of the 

 forest, 1.3 ." These investigations are, in a measure confirmatory 

 of my own. 



Forests produce abundant dews. The 'formation of dew is 

 dependent on two conditions, the radiation from objects near the 

 earth and a certain proportion of moisture in the air. Just as in 

 the case of the production of rain, the moister the air the more 

 readily is dew formed, it requiring a less reduction of tempera- 

 ture, hence when the moistened atmosphere in the vicinity of a 

 forest comes in contact with the night air, dew in abundance is 

 the result. Having shown that the temperature of the trees, 

 their leaves and the atmosphere in the woods is several degrees 

 lower than the air without, it may be inferred that dew is fre- 

 quently formed during the day in the shade, and, perhaps, over 

 the forest, particularly when the atmosphere is tranquil or when 

 there are but slight breezes, shedding its silent enlivening influ- 

 ence to fields and valleys round about. This is another office on 



