720 



those of M. de Humboldt at the equator, but 

 the hours of variation differ according to the 

 seasons ; the tropical hours for winter, are at 9 h 

 in the morning, 8 h in the afternoon, and 9 h in the 

 evening. In summer the lowering appears to 

 begin at 8 h in the morning, is continued till 4 h in 

 the afternoon, and begins again at 10 h in the 

 evening. My observations being made alone, 

 it was impossible for me to determine the noc- 

 turnal variations with sufficient precision ; for 

 in our climates, whole months of assiduous 

 observation do not suffice to limit the quanti- 

 ties which one single night of the equator fur- 

 nishes in all their purity T 



All the remarks of M. Ramond on the epochas 

 of the extreme limits, and the small changes 

 which these epochas undergo in winter and 

 summer, have been perfectly confirmed by the 

 observations made from 1817 to 1821, at Tou- 

 louse, by M. Marque Victor, and from 1822 to 

 1823, at Chambery, by M. Billiet. The former 

 collected more than 20,000 barometric heights, 

 of which the results are inserted in the compte 

 rendu of the labors of the Academy of Toulouse. 

 He observed from six in the morning till mid- 

 night, from hour to hour, with extraordinary 

 assiduity and patience. At Toulouse, as at 

 Chambery, and at Clermont in Auvergne, the 

 diurnal maxima and minima draw nearer to 

 noon more than an hour, in winter, when the 



