62 BPPECTa OF FORESTS ON HUMIDITT. 



" M. Mathieu, sub-director of the Forest School, has undertaken a 

 series of experiments under vary favourable conditions. Of these the 

 following is one which is particularly interesting, and one, the results 

 obtained by which scarcely agree with those of Marshal Vaillant. 

 Two udomfetres were placed at the forest station of Ginq-Tranoh^es, 

 the one in the open wood, under a patch of beeches and hornbeams, 

 of average denseness, and of the age of 42 years ; the other, at a 

 little distance, in the middle of an open space many hectares in 

 extent. It may be well to note that the forest udomitre is of special 

 construction; that the receiver embraces the stem of one of the 

 perches of the clump, and presents a surface quite equal to the 

 projection of the top of the tree ; that by this means the indications 

 of the instrument are quite exact, and represeut well, without 

 exaggeration or diminution, the depth of the sheet of water rpceived 

 by the wooded ground ; and that this water, dropping from leaf to 

 leaf, passes through them, or flows down the truuk. 



" Under these conditions the udombtre gave, in 1868, the following 

 quantities of rain : — 



MEASURKMENT OF BAIN. 

 Months. Under wood. Outside wood. Proportion. 



miliimHret, mm. mm. 



January, 68 73 0-931 



February 37 36 1-025 



March 50 50 1 



April, 69 73 -945 



May, 8 8 1 



June, 48 52 -923 



July, 31 34 -911 



August, 26 37 -702 



September 59 61 -962 



October 118, 122 -967 



November, 26 28 -928 



December, 163 174 -936 



Total, 703 749 -939 



" It may be astonishing to see in the table that during the months 

 of February, March, and May the sheltered pluviom&tre received as 

 much or more rain than tlie pluviomfetre in the open space ; it is 

 necessary to consider that, either through some caprice of the rain 

 or by some such effect of the trees, there fell more water iu the wood 

 than in the adjacent open space, This result, moreover, mi^ht 



