456 



petty. But the means I employed deserved 

 little confidence. The wind of Petare coming 

 from the east and south-east, by the eastern 

 extremity of the valley of the Guayra, brings 

 from the mountains and interior of the coun- 

 try a dryer air, which dissipates the clouds, 

 and the summit of the Silla rises in all it's 

 beauty. 



We know that the modifications brought by 

 the winds in the composition of the air, in va- 

 rious places, entirely escape our eudiometrical 

 experiments ; the most exact of which can esti- 

 mate only as far as 0*003° of oxygen. Che- 

 mistry does not yet possess any means of dis- 

 tinguishing two jars filled, one with the air of 

 the sirocco or the catia, and the other before 

 these winds are felt. It appears to me proba- 

 ble, that the singular effects of the catia, and 

 of all those currents of air, to the influence of 

 which popular opinion attributes so much im- 

 portance, must be looked for rather in the 

 changes of humidity and of temperature, than 

 in chemical modifications. We need not have 

 recourse to miasmata brought to Caraccas from 

 the unhealthy shore on the coast : it may be 

 easily conceived, that men accustomed to the 

 drier air of the mountains and the interior, 

 must be disagreeably affected, when the very 

 humid air of the sea, pressed through the gap 

 of Tipe, reaches in an ascending current the 



