ON THE RAINFALL. 305 



cross the breadth of the circle from left to right, or from right to left, 

 as the case may be ; the air forming the rear will cross the breadth 

 of the circle in the opposite direction, and scatter the hailstones or rain 

 over the whole breadth traversed in two showers, minutes, hours, or 

 days apart ; but at the sides the wind blows in but one direction 

 on the right of the circle, and in one direction, the opposite of this,^ 

 on the other, and along the lines followed by these the hail or rain 

 falls continuously in greater abundance." 



M. Cezanne writes in reference to what he had stated relative to 

 the fall of rain being determined in a great measure by the contour 

 of a country, and which I have already quoted : — 



" It may be said — if the rain acted as if it had caprices and the 

 protuburances of the soil caused a change in the pluvial current — 

 will a mass of forests which raises itself on the plain remain without 

 any influence 1 Stating the question thus, it must be admitted as un- 

 questionable that forests may exercise an influence on the rainfall. It 

 may so happen, for example, that a forest of trees coming to bar up a 

 valley of little depth may interrupt the pluvial current, and notably 

 diminish the quantity of water collected in a pluviometer which would 

 be placed behind it. The town of Erfurt, for example, sheltered 

 against the west wind by the Thuringian forest, receives less rain than 

 do adjacent regions.* It is not necessary to speak of a high forest of 

 timber trees ; a simple wall, suitably disposed, suffices. It is well 

 known that the face of such a wall, exposed to the pluvial wind, re- 

 ceives more rain than does the sheltered side, — what is kept on the 

 one side falling there leaving so much the less to fall on the 

 other ; and observations show that it is enough to raise up buildings 

 or other erections in the neighbourhood of a pluviometer to produce 

 a change in its receipts." 



But the hail-storm cited by Renou was not a fall of rain produced 

 by a pluvial wind blowing along the surface. The hail was produced 

 at an elevation far above the loftiest forest, where the forest could 

 not pi'oduce such a deviation as he states did not occur. 



And with regard to his belief that it is beyond the power of man 

 to exercise the least influence over physical phenomena, the expression 

 given of it would require some qualification in order to exempt at least 

 such physical phenomena as are mentioned by M. Cezanne in the state- 

 ment by him which I have just cited, and who holds the same opinions 

 as does M. Renou on the point to which I understand him to refer. 



* Kaemiti. 



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