Cu. VI. SOUTH AMERICA. 73 



at some distance from it ; so that these vapours are 

 to be considered, on one hand, as yielding; to the 

 current of the air^, and on the otlier, as ascending 

 in proportion to the rarefaction they have received 

 'from the rays of the sun. Hence it foliows, that 

 these vapours cannot be those which are most con- 

 densed, as the difficulty of rising is always propor- 

 tional to the degree of condensation ; and at the same 

 time their magnitude woidd render them more sus- 

 ceptible of the impulse of the wind. So that these 

 consequently being the most subtile or tenuious, on 

 having passed that region, the celerity with which 

 they were before carried upwards is decreased, and 

 great numbers of them being united, form that lofty 

 mist which is seen after the cloud is totally dissipa- 

 ted. This mist cannot be converted into rain; for 

 having passed above the region proper for its forma- 

 tion, all the parts become congealed, and their 

 weight can never be increased suiHciently to over- 

 come the resitance of the air which supports them; 

 for the quantity of fno¿e which have overcome this 

 obstacle being inconsiderable, they cannot be united 

 with a sufficient quantity of others to withstand the 

 continual dissipation occasioned by the action of the 

 rays of the sun. Nor can they descend in either 

 sftow or hail, as raiglit be expected from their pre- 

 sent state. Besides following always, though with less 

 velocity, the current of the wind, any such concre- 

 tion oif them as to form a thick cloud Us prevented : 

 for as we have already observed^ these mists are so 

 tenuious, as to afford in the day-time a confused view 

 of the disk of the sun, and of the stars in tjie night. 



In order to render the premises agreeable to ob- 

 servation, one difficulty still remains, namely, that 

 those lofty mists are seen only in winter, and not in 

 summer. But this, in my opinion, must naturally 

 be the consequence ; for besides the general reason 

 that the stronger influence of the rays of the sun dis- 

 perses 



