334 



during our second residence at Cuniana, after 

 having observed, on the 26th of September, 

 1800, the immersion of the first satellite of -Ju- 

 piter*, succeeded in seeing the planet distinct- 

 ly with the naked eye, eighteen minutes after 

 the disk of the sun had appeared in the hori- 

 zon. There was a very slight vapour in the 

 east, but Jupiter appeared on an azure sky. 

 These facts prove the extreme purity and trans- 

 parency of the atmosphere under the torrid 

 zone. The mass of diffused light is so much 

 less, as the vapours are more perfectly dissolved. 

 The same cause, that weakens the diffusion of 

 the solar light, diminishes the extinction of that 

 which emanates either from a bolis, Jupiter, or 

 the moon seen on the second day after her con- 

 junction. 



The day of the 12th of November was ex- 

 tremely hot, and the hygrometer indicated a 

 very considerable dryness for those climates -J~. 

 The reddish vapour clouded the horizon anew, 

 and rose to the height of 14° v This was the 

 last time it appeared this year ; and I must 



* I observed it at 5 h 10' 8* mean time : long, of Cnmana, 

 deduced from the tables of Delambre, 4 h 25' 57" (Ast. Ob., 

 Vol. i, p. 80). 



t At nine in the morning, cent, therm. 26*2° ; hygr. 66 4°. 

 At one, therm. 29° ; hygr. 81°. The scale of Saussure's 

 hygr. is always meant, when the contrary is not expressly 

 mentioned. 



