PRODUCED BY MAN. 803 



die Regenmenge zu, er hat desshalb iin Gebirge einen grosseren Werth als im Ebenen 

 Im Sommerhalbjahr ist die Einwirkung des Waldes auf die Regenmenge viel grosser 

 als im Winterhalbjahr.' 



Whatever the physical principles involved are, anybody may find 

 beautiful illustrations of them, who will observe in a mountainous 

 district how — 



or how 



' The swimming vapour slopes athwart the glen, 

 Puts forth an arm and creeps from pine to pine, 

 And loiters slowly drawn ^,' 



* The light cloud smoulders on the summer crag ^,' 



recollecting that the phrase ' Rauchen der Walder ' is used for the 

 similar phenomenon when produced by trees, or who will finally in 

 a lowland or other country stand and study the frost as it hangs 

 itself on to such a tree as the birch often long before it has begun 

 to whiten the ground around it. 



[Since writing as above, the ' Observations Meteorologiques faites 

 de 1 877-1878,' by M. Fautrat, published by the French ' Ministers 

 de I'Agriculture et du Commerce : Administration des Forets,' 1878, 

 have come into my hands. This author, with the results of M. Ma- 

 thieu's eleven years^ observations at Nancy (for which see his ' Me- 

 teorologie Comparee Agricole et Foresti^re,' published under the same 

 auspices, February 1878) before him, as also the results of four years' 

 observations in the Forest of Halatte, and of three years in the pine-^ 

 woods of Ermenonville, has come to the following conclusions. 



i. That when it rains more rain falls over a wooded than over a 

 non-wooded area, and that whilst trees of all kinds possess the 

 power of condensing vapour, broad-leaved trees produce less effect 

 than is produced by the narrow-leaved Coniferae (pp. 14 and 16). 



ii. That as regards the hydrometric condition of the air, the air 

 over a wooded area contains more watery vapour (p. 18) than that 

 over an unwooded area, but that the coniferae have more watery 

 vapour in their circumambient atmosphere than the broad-leaved 

 trees. M. Fautrat expresses, or rather expands, this fact in the 

 following words : — 



' If the vapour dissolved in the air was visible as are mists, we should see the 

 forests surrounded with a vast screen of moisture, and around the Coniferae this 

 envelope would be more marked than over the broad-leaved trees. What is the 

 source of this vapour 1 Does it come from the soil ; is it the result of evaporation 



1 Tennyson, 'GEnone.' ^ Tennyson, • Edwin Morris,' 



3 f:j 



