296 



M. Humboldt on the Horary 



mond has ascertained that the barometer is highest in January 

 and June, and lowest in April and November. 



The next subject of M. Humboldt's inquiry, is to ascer- 

 tain if these horary variations have any connection with the 

 lunar motions. M. Toaldo had long ago averred, that, in 

 Italy, the barometer was much higher in the quadratures than 

 in the syzigies, and in apogee than in the perigee ; but the 

 results of the observations of MM. Boussingault and Rive- 

 ro made at Bogota on the subject, by no means confirm the 

 opinion of Toaldo. They were made in the last five months 

 of 1 823, and the first seven months of 1824, and the following 

 are the results : 



In a letter from M. Boussingault to Baron Humboldt, dated 

 Bogota, February 9, 1825, he says, " I dare not deny that 

 there is any lunar influence on the mean weight of the mer- 

 cury ; but I believe that this influence, if it does exist, is 

 scarcely perceptible, because it is lost among the other causes 

 of the horary variations." 



"We shall now conclude this article with Baron Humboldt's 

 very interesting summary of the laws, or the general relations 

 of this class of atmospherical phenomena. 



1. The horary variations of the barometer are felt in all 

 parts of the earth, in the torrid, as well as in the temperate and 

 frigid zones ; at the level of the sea, and at heights above 

 200 toises. The two atmospherical tides are not generally of 

 equal duration. In comparing results of unequal accuracy, 

 and obtained by thirty different observers, between 25* of S. 

 lat., and 55° of north lat., we find, for the epochs of maxi- 

 mum and minimum deviations of two hours. By excluding 

 five results only, the maximum in the morning falls between 

 8% h and 10i h , the minimum in the afternoon between 3 h and 

 5 h ; the maximum in the evening between 9 h and ll h , and 

 the minimum in the morning between 3 h and 5 h . As the 

 most correct type, we may adopt for the equatorial zone, 



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