ON THE METEOROLOGY OF PORT LOUIS, 



131 



Table XIII. — Showing the Mean Vapour-pressure for each Month and 

 Year, derived from Six-hourly Observations taken daUy from 1860 to 



1866, both inclusive. 



The above Table, as already remarked, indicates a gradual decrease of the 

 vapour-pressure. This becomes more evident when we take the means for 

 consecutive periods of two years each. Thus : — 



Years. 

 i860 

 1861 

 1862 

 1863 

 1864 

 1865 



Yap. -pressure. 

 •680 1 



•655/ ••■ 

 •663 1 



•643 1 

 •655/ ■■■ 



Means. 

 •667 



•657 



•649. 



The pressure for 1866 (•619) is so much lower than the greatest (-680) 

 that it is very probable the mean pressure for 1866 and 1867 will bo the 

 least of aU. 



It is possible that this diminution of vapour -pressure may be owing to 

 the great extent to which the primeval forests have been cut down during 

 the last twenty years. As the rains are evaporated and carried away sooner 

 than they would bs if protected from the sun's rays, we may suppose that the 

 mean annual amount of vapoiu' in the air must be less than it was before 

 the forests were cut down ; and that if this is the case at Port Louis, on the 

 west coast, it miist be still more so in the interior of the island, where the 

 forests existed. 



