EPPBCTS OP INCIDENCE. 163 



received less water than the latter, and further, that in this case the 

 arrangement of the sides of the mountains exercised a prepon- 

 derating influence, and one which masked that of the forests." 



M. Cezanne has given attention to the efiect of the configuration 

 of the land upon the quantity of the rainfall. He has shown that this 

 is determined, not only by altitude, but by the incidence with which a 

 pluvial wind may strike upon any precipice or slope which opposes it, 

 the rainfall being greater in proportion as the atmospheric current 

 arrested by an obstacle is compelled to rise more rapidly. Hence 

 the objection stated by him. 



Some, if not all, of the so-caUed caprices, to which M. Cfezanne refers 

 (while I consider the designation, which originated not with him, not 

 altogether appropriate), I shall afterwards have occasion to cite, and 

 also the experiments niade by M. Belgrand. Here it is enough to 

 have established that the popular opinion in regard to the effect of 

 forests on the rainfall has received support from scientific observa- 

 tions, but that it may require considerable modification to bring it 

 into perfect accordance with the matter of fact. 



It is with this as it is with many other popular observations on 

 the weather, which may be said to embody correct observations, but 

 which have this solid substratum of truth overlaid with much which 

 is not entitled to be considered such — the confiding trust with which 

 they are received and propounded may be attributable to the 

 conKdent and explicit expression in which they are couched. The 

 uneducated are often impatient of dubiety, or want of explicitness of 

 thought ; and they are ready to impose this upon a vague or ambiguous 

 statement with which they are not satisfied ; and the half- 

 educated, again, are prone to generalise rashly, and go far beyond 

 what strict induction would warrant. Education by philosophy may 

 regulate this tendency and make it productive of good ; and the 

 study of science may train the educated man to suspeud his 

 judgment in regard to the absolute, while resting with full confidence 

 on ascertained facts. The generally received opinions in regard to 

 the effect of trees on humidity, to the extent to which they have 

 been confirmed by observations, are accepted and issued recoined, 

 with a new impress, by such men of science ; but the impress on the 

 coin, limits, while it defines its value, and to pass them as equivalent 

 to more than their determined value; were to mislead, though there 

 might be no intention to deceive. The statement made by Mr 

 Marsh, and the testimony of M. Mathieu, seem then to coufirm and 

 limit, the popular opinion in regard to the effect of forests upon the 



