THE FOREST AND SPRINGS 365 



at various altitudes, indicating in an exact manner the quantity of rain which falls 

 into the two basins." 



The observations are made daily, and were begun in 1900. 



There wiU, in the future, perhaps be occasion to simplify the depositary employed for 

 the gauging of the outflow by substituting, for example, self -registering apparatuses for 

 the intermittent measurements now being effected. ^^ 



It is also doubtful whether these two little streams exactly give off (in the visible 

 part of their course) all the water which filters into their basins. It is probable that 

 it is so; but no one can positively assert that there does not exist some fissure of the 

 subsoil where masses of water accumulate, by means of which they are lost, and escape 

 observation. The installation of rain-gauges in a wooded region would also be very 

 difficult if one wished to collect all the water drawn from the atmosphere by condensa- 

 tion on the branches, water of which only a part reaches the soil by rolling down the 

 trunks, etc. This does not prevent the experiences gained in the Emmenthal from 

 constituting an essay of ih^ greatest interest, in view of the solution of a question as 

 controverted as it is important. The installation of these instruments will be epoch 

 making in the science of forestry, and one cannot but be grateful to Professor Bourgeois 

 for taking the initiative in an experiment which we hope will not remain isolated. It 

 is with impatient curiosity that we await the result of the measurement in the two little 

 basins of the Bernese Emmenthal. 



In view of the difficulty which the direct study of the influence of forests on the feed- 

 ing of springs presents, an attempt has been made to simplify the question by examining 

 how the presence of woodlands modifies the cUfferent factors uponjwhich the abundance 

 of springs depends. 



This abundance is evidently the result (Ij of the quantity of water which comes from 

 the soil; (2) of the proportion of this water which, having filtered through the ground, 

 has reached the subterranean sheet, of which the springs are apparently the overflow. 

 Our study therefore divides itself naturally into two parts. The first concerns that 

 which is known of the influence of forests on the quantity of water which reaches the 

 soil. The second is devoted to the influence of forests on the proportion of that water 

 which filters through to the subterranean sheet. These two elements of the question 

 will form the subject of the following paragraphs. 



Influence of Forests on the Quality of Atmospheric Water which Reaches the Soil. — 

 Water which reaches the ground is derived from three principal sources: 



1. From rains, snows, hail, etc., which, forming on the upper strata of the atmos- 

 phere, are precipitated on the ground. 



2. From the condensation of vapor upon the surface of vegetation, when this is 

 colder than the air itself; water thus condensed reaches the ground in a solid or in a 

 liquid condition, in the latter case either in falling through the air or in roUing down 

 stalks. 



"The gauging apparatuses were installed under the direction of "M. rmgenievu" en 

 chief de Morlot," according to the plans of "M. Tingenieur Epper," employed in the 

 Federal service. When the outflow is weak it is directly measured by diverting the 

 waters into a gauged basin and noting the mass of water coUected in a given time; 

 when the water is plentiful it is made to run through one or two or three channels, 

 terminating in orifices with rectangular sections where the outflow is calculated accord- 

 ing to the formula indicated by the French engineer, M. Bazin ("Annales des Fonts et 

 Chaussees, Vol. XVI, 18S8, and XIX, 1890), by estimating the bulk of the sheet of 

 water passing on to the waste weir. 



1^ Since our first visit to the Emmenthal in 1900 the wish expressed above has been 

 gratified. In April, 1903, self -registering apparatuses have been installed on the two 

 streams; at the same time the apparatuses for gauging the snow and rainfall in their 

 basins have been improved. 



