186 



sphere, as compared to that at the surface (which is in each case as- 

 sumed to he represented hy TO), supposing the air to be everywhere 

 saturated with moisture, and the reduction of temperature for ascent 

 to be 3 for 1000 feet. To these calculated ratios are added those 

 actually observed by Dr. Hooker in the Eastern Himalaya, and by 

 Mr. Welsh in his balloon ascents *, as already given in a preceding 

 page. 



TABLE II. 

 Proportion of Vapour at various Altitudes. 



In Table III. the results of Dr. Hooker's and my own observations 

 are given in more detail. 



The accordance between the calculated and observed quantities of 

 vapour shown by these figures is so close, that we can have no hesi- 

 tation in admitting that Dr. Hooker's conclusion will, in all proba- 

 bility, be found to afford the general solution of this problem. The 

 relative quantity of vapour in the case of his observations having 

 been rather greater in the higher than in the lower strata of the 

 atmosphere, is a circumstance which cannot be held to affect the 

 general truth of our conclusions, as will be perfectly accounted for by 

 supposing that the diminution of temperature with height was less 

 rapid in reality, than 3 for 1000 feet, on which my calculation is 

 based. It is further worthy of notice, that the calculated proportion 

 of vapour at various altitudes varies but little even with considerable 

 change of the surface temperature, though there is a manifest ten- 



* Phil. Trans. 1853, p. 311. 



