1836.] On the land toinds of Commanded 33 



This experiment though correct so far as it goes, is I con- 

 ceive, one of those most apt to mislead, and thereby impede 

 the attainment of just views in science, by not guarding 

 against the sources of fallacy to which it is exposed. Ac- 

 cording to the theory I ventured to propose, the heat and 



I dryness of the country necessarily form one of its elements, 

 by rarifying the super-incumbent stratum of air, and causing 



. as it were, a partial vacuum giving rise to a rush of cold moist 

 and dense air from the mountains, to equalize the pressure. 

 The cold air of the mountains mixing with the heated air of 

 the plains, becomes in its turn rarifled, and in the same pro« 

 portion has its capacity to absorb and retain moisture in* 

 creased. This or something approaching to it, if I mistake 

 not, is the commonly received opinion, but has hitherto been 

 considered unsatisfactory on account of occasional anomalies 



\ which it either does or seems to present. I stated that the 



i remarkable dryness of the air at Courtallum had been long 

 observed but never satisfactorily explained. The explanation, 

 I gave, I still consider correct, because the same wind which 

 is cool and even loaded with moisture there, has acquired the 

 heat and dryness, peculiar to the land winds, by the time it 

 reaches Palamcottah, only 30 miles distant, thus proving the 

 truth of the theory by demonstrating what has hitherto been 

 matter of conjecture only. I certainly have not put it to the 

 test of experiment, because I had it not in my power, but I 

 have no hesitation in stating as my conviction, that if tried 

 in the usual way at Courtallum, there would be a copious 

 deposition of dew proving the supposed dryness only appa- 

 j rent ; while at Palamcottah the instrument would indicate 

 nearly absolute dryness, the same as at Hyderabad. I say, if 

 \ tried in the usual way, for in using the instrument both balls 

 are equally exposed to the current of air* If the air is only 

 moderately rarified as at Courtallum from its proximity to 

 the cool and moist atmosphere of the Malabar monsoon, 

 its capacity for moisture is but little increased, and the re- 

 duction of a few degrees of heat would produce a more rapid 

 deposition, than the simultaneous evaporation would remove, 

 but at Palamcottah in similar circumstances, owing to the 

 more highly r^yified state of the air^ and its greater capacity 



