Effects of Vegetation on Climate. 161 



The probability expressed by it is an altogether different pro- 

 bability from what he asserts. His calculations are also 

 apparently inaccurate, in some instances at least. 



(2.) All the numerical deductions of his successors are 

 equally baseless. 



(3.) Were Mitchell's principle just, a perfectly uniform 

 and symmetrical disposition of the stars over the sky would 

 (if possible) be that which could alone afford no evidence of 

 causation, or any interference with the laws of " random ;" — 

 a result palpably absurd. 



(4.) Special collocations, whether (a) distinguished by their 

 symmetry, or (/3) distinguished by an excessive crowding to- 

 gether of stars, or the reverse, inevitably force on the rea- 

 soning mind a more or less vague impression of causation ; 

 — an impression necessarily vague, having nothing absolute, 

 but depending on the previous knowledge and habits of 

 thought of the individual, therefore incapable of being made 

 the subject of exact {i. e. mathematical) reasoning. 



Probable Effects of Vegetation on Climate. 



Meteorologists throughout India had for some time been engaged 

 in examining the probable effects of vegetation and of moisture on 

 climate, and the following results, mainly from an able paper by Dr 

 Balfour of Bombay, and the Edinburgh New Philosophical Journal, 

 gives a general outline of the present state of our knowledge on this 

 subject. 



The fall of rain at the elevations of 2000 to 4500 feet, on ridges 

 exposed to currents of wind from the sea, amounts to about 200 

 inches annually ; it decreases, both as we ascend and as we proceed 

 into the interior. Along the shores of Hindoostan it averages betwixt 

 sixty and eighty. On the tolerably fertile or rarely wooded por- 

 tions of the great plateau, it amounts to betwixt twenty and thirty- 

 five. At Bellary, it averages from ten to fifteen ; and when we in- 

 quire the cause of this sudden diminishment, we find that the dis- 

 tricts around are destitute of trees, and nearly devoid of all sorts of 

 moisture or local vegetation. Humboldt, in noticing the barrenness 

 and extreme aridity of the vast plains approaching the Orinocco from 

 the Andes, lat. 9°, states, that the people assured him that the fall 

 of rain had diminished within the last century, and that since the 

 Spanish conquest, the trees, formerly abounding, have been destroyed. 

 The earlier settlers in Carracas are well known to have destroyed 

 the climate by removing the trees ; rain formerly abounded where now 



VOL. L. NO. XCIX. — JANUARY 1851. L 



