722 



strument, and the choice of the hours (21 h and 

 4 h ), as the most instructive which we hitherto 

 possess, the mean of the two decades suffices to 

 shew that the mercury sinks between 9 h in 

 the morning, and 4 h in the afternoon ; but in 

 order to determine the quantity of variations, 

 to know if the maximum is attained at 9 h or at 

 ll h , requires more days of observation in the 

 temperate zone than M. Parrot could devote at 

 Milan. 



III. Extent of the horary variations. In col- 

 lecting the whole of my observations at Cuma- 

 na, I find, for that part of the tropics, and at the 

 level of the sea, the extent of the variations re- 

 duced to zero of temperature, from 9 b in the 

 morning till 4 h in the afternoon, to be L10 H or 

 2.47 m . I shall add to the results of Cumana 

 those of Caraccas, corresponding to an eleva- 

 tion of 408 toises. 



