432 



Influence of forests upon rain-fall. — In a note npon this sub. 

 ject presented to the French Academy of Sciences * by MM. L. Fantrat 

 and A. Sartiaux, they give the results of some interesting observations 

 made in the forest domain of Hallette and upon a neighboring culti- 

 vated section of country. Becquerel declares that forests increase the 

 amount of rain-fall, while Vaillaut insists that they diminish it, and 

 Mathieu concludes from his researches that the amount of rain-water 

 received by forests is equal to or even greater than that received by the 

 open country. Dausse states that rain is formed when warm and moist 

 winds encounter cold strata of air ; the air of forests being cooler and 

 more humid than that of uncovered soil, a greater quantity of rain 

 should fall in such localities. In order if possible to settle the point thus 

 disputed, the authors have made observations: first, above a wooded sec- 

 tion ; and, second, at the same elevation at a distance from this section 

 so slight that the differences observed can be due to the influence of the 

 forest alone. In order to carry out these observations they placed, at an 

 elevation of about 6 meters above a collection of oaks and elms which 

 were of about twenty years' growth and about 8 or 9 meters high, a 

 pluviometer, a i^sychrometer, an evaporometer, and maximum and 

 minimum thermouieters, to determine the quantity of rain-fall, the 

 amount of moisture in the air, andthe variations of temperature and evapo- 

 ration. At a distance of 300 meters from the forest, at the same eleva- 

 tion, the same instruments were placed under the same conditions over 

 an open country. 



The following table shows the results of their observations : 



Quantity of rain-fall. 



Date. 



Above 

 wooded sec- 

 tion. 



300 meters 



from wooded 



section. 



1674 — February 

 March . . . 



April 



May 



June 



July 



Total 



Mi 



lUmeters. 

 18.75 

 1.5. 00 

 27.50 

 39. 25 

 51. 25 

 40.75 



Millimeters. 

 18.00 

 11.75 

 25.75 

 35.50 

 48. 25 

 37.75 



192. 50 



177. 00 



Difference in favor of forest, 15.50 millimeters. 



Degree of saturation of the air. 



Date. 



Above 



tbe wooded 



section. 



300 meters 



from wooded 



section. 



1874— March 



April 



May 



June 



July 



Total ... 



Average 



Centimes. 

 71.1 

 64.3 

 64.1 

 60.9 

 54.6 



Centimes. 

 70.0 

 64.2 

 60.4 

 60.1 

 53.8 



315.0 



308.5 



63.0 



61.7 



Difference in favor of forest, 1.3 centimes. 



Comptes rendus, t. Ixxix, 409. 



