436 



dians have been transformed into Amoizanas, or 

 Amazons ; and the Rio Idapa has been made to 

 rise from a spring, which, the moment it issues 

 out of the ground, divides itself into two 

 branches, the courses of which are diametri- 

 cally opposite. This bifurcation of a spring is 

 altogether imaginary. 



We stopped near the raudal of Cunuri. The 

 noise of the little cataract augmented sensibly 

 during the night. Our Indians asserted, that 

 it was a certain presage of rain. I recollected, 

 that the mountaineers of the Alps have great 

 confidence in the same prognostic *. In fact, it 



* ,( It is going to rain, because we hear the murmur of 

 the torrents nearer." say the mountaineers of the Alps, like 

 those of the Andes. Mr. Deluc has tried to explain this 

 phenomenon by a change in the barometric pressure, by an 

 increase in the number of the bubbles of air, that burst at 

 the surface of the water. (Modificat.de V Atmosphere, § 1031.) 

 This explanation is equally forced and unsatisfactory. I 

 will not attempt to replace it by another hypothesis, but I 

 shall observe, that the cause of the phenomenon is a modifi- 

 cation of the atmosphere, which has an influence at once on 

 the sonorous and on the luminous undulations. The prognostic 

 drawn from the increase and the intensity of sound is inti- 

 mately connected with the prognostic drawn from a less ex- 

 tinction of light. The mountaineers predict a change of wea- 

 ther, when, the air being calm, the Alps covered with per- 

 petual snows seem on a sudden to be nearer the observer, and 

 their outlines appear with great distinctness on the azure 

 vault of the sky. What is it, that causes the want of homo- 

 geneity in the vertical strata of the atmosphere to disappear 

 instantaneously ? 



