366 APPENDIX 



3. From condensation taking place on the superficial parts of the soil itself, upon 

 its covering of dead leaves, where the ground is wooded. 



We will begin by discussing this last source of the feeding of the soil by water, not 

 because it is without importance, but because its relative importance has not yet been 

 discovered. 18 



> In the previous chapter it has been shown in detail, that the presence of forests 

 increases the rainfall in a very marked degree. 



This result has been incontestably obtained, at least in the case ^unique it is true) " 

 noted at the Research Station of Nancy. During 33 consecutive years, without any 

 divergences, it has been proved by observation that, while in the center of the forest of 

 Haye (17,297 acres of beech, hornbeam, and oak) there is a rainfall of 33.4 inches an- 

 nually in the open, on a piece of ground cleared for about 5 acres, while on the other 

 hand only 31.4 inches fall on the borders of the forest, and 25.6 on a similar piece of 

 ground some distance off; and it is to be remembered that this difference in the rainfall 

 occurs in the same ratio, each year at every season, whatever may be the direction of 

 the winds, and is only slightly altered without being reversed by the total amount of 

 rainfall during the year. 



The measurements of M. Fautrat, also given above; those of M. de Pons in the forest 

 of Trongais (Allier) although less reliable because they extend over a smaller period of 

 years; as well as many others carried out in Germany, Austria, and Russia, in Anglo- 

 India, etc., lead one to believe that this phenomenon is common to all countries. 



If the summits of wooded masses are more bedewed than the neighboring fields, 

 does the same hold good for the soil in a forest? 



Here, incontrovertible -observations are much more rare. 



It is not enough in fact, to place a rain gauge under the trees in order to arrive at 

 even an approximate idea of the quantity of water which reaches the soil of the forest. 

 As Mathieu already observed 30 years ago, the quantity of water collected will vary 

 in a singular degree, according as one puts the rain gauge near the trunk sheltered under 

 the network of big branches, or under a gap in the leafage of the summits, or under the 

 center of a branch, or at the extremity of this same branch which will drain into it 

 like a gutter, in emptying into it all the water or all the snow fallen on its surface, and 

 upon that of the upper branches. M. Boppe 18 has shown that rain gauges placed under 

 the same tree, at very short distances from one another collect quantities of water 

 varying to an unbelievable degree. 



Finally a procedure such as this does not take into account the quantity of water 

 which reaches the soil by running down stalks, and whose proportion may be 15 to 20 

 per cent, perhaps even more of the annual rainfall, even if this water is derived from 

 rain, or is directly drawn from the atmosphere by means of condensation on leaves or 

 on stalks. 



It is for this reason that no mention will be made here of the results obtained in 

 France or abroad by means of ordinary rain-gauges placed under trees. The only 



16 Giseler, quoted by M. Ney ("Der Wald und die Quellbildung," Metz, 1901), has 

 proved by experiment that in a tube of glass maintained at c., and placed in a room 

 where the temperature remained uniformly equal to 4, 5 c. a quantity of water was 

 condensed in one year equal to a rainfall of 13.8 inches. It is superfluous to remark 

 that this experiment as well as many others effected in laboratories in the cause of 

 agronomy have no real value. Things happen entirely differently in nature, than in 

 the conditions rendered obligatory for the purposes of experiment. 



17 Since January 1, 1903, new experiments have been undertaken upon our initiative 

 at different points of the French Vosges, with a view to verifying the generality of the 

 facts observed in the neighborhood of Nancy. 



18 "Regenmessungen unter Baumkronen," llth number of the " Mitteilungen 

 aus dem forstlichen Versuchewesen Oesterreichs," Vienna, 1896. 



