VARYING QUANTITIES OP RAIN. 161 



which the vapour is raised by the solar heat. The winds are the 

 guiding tubes, which cany the vapour to the forests, where lower 

 temperature prevails. This naturally condenses the vapour ; and 

 showers of rain are thus distilled from the cloud masses, which float 

 in the atmosphere, by the woods beneath them." All which is true. 



By Marsh it is said: — "We cannot positively affirm that the 

 total annual quantity of rain is even locally diminished or increased 

 by the destruction of the woo Is, though both theoretical considera- 

 tions, and the balance of testimony, strongly favour the opinion that 

 more rain falls in wooded than in open countries. An important 

 conclusion, at least, upon the meteorological influence of forests, is 

 certain and undisputed : the proposition namely, that within their 

 own limits, and near their own borders, they maintain a more 

 uniform degree of humidity in the atmosphere than is observed in 

 cleared grounds : scarcely can it be questioned that they tend to 

 promote the frequency of showers, anl, if they do not augoaeut the 

 amount of precipitation they probably equalize its distribatioa 

 through the different seasons." 



" The strongest direct evidence which I am able to refer to in 

 support of the proposition that the woods produce even a local 

 augmentation of precipitation, is furnished by the observations of 

 Mathieu, sub-director of the Forest School at Nancy. His pluvio- 

 metrical measurements, continued for thi-ee yeai-s, 1866-1868, show 

 that during that period the annual mean of rainfall in the centre of 

 the wooded district of Cinq-Francheas, at Belle Fontaine on the 

 borders of the forest, and at Amance, in an open cultivated 

 territory in the same vicinity, was respectively as the numbers 1000, 

 957, and 853." In an appendix, Mr Marsh inserted a statement that 

 •' Fautrat and Sartiaut placed at an elevation of six metres above a 

 grove of oaks and elms, of twenty years growth and eight or nine 

 metres height, in the forest doiniin of Hilette, pIuviom&::res and 

 other meteorological instruments, and like instruments at the same 

 elevation in the open ground three hundred metres from the forest. 

 In the months February to July inclusive, the rainfall above the trees 

 was found to be 192, 50"^'^ and during the same period ITTmm in the 

 open ground. Comptes-Rendus, t, LXXIX, 409. 



The observations made by Mr Mathieu are thus summed up by 

 himself, in his report to the Director-General of the Forest Adminis- 

 tration : — 



" In 1868 there fell on cleared spaces within the forest region more 

 rain than beyond the borders of this ; on agricultural land the fall was 



q 



