764 



limits of the descending oscillations. The in- 

 terruption of the horary oscillations near the 

 tropic of cancer (in the gulph of Mexico) is a 

 prognostic of the proximity of tempests, of their 

 force and duration. The monthly means of the 

 barometric heights diminish regularly from 

 July to December and January, on the table- 

 land of Bogota (p. 739), and even in the south- 

 ern hemisphere, on the coast of Rio Janeiro (p. 

 731). The blowing-back of the north winds at 

 the extremity of the northern equinoxial zone, 

 raises the mean of December and January, 

 above that of July and August (p. 726 and 748. 



9°. Within the tropics, as well as in the tem- 

 perate zone, in comparing the extreme swerv- 

 ing of the barometer from month to month, we 

 find the limits of the ascending oscillations 

 two or three times nearer than the limits of the 

 descending oscillations # . I 



10°. The observations hitherto collected have 

 not indicated a sensible influence of the moonf- 



* According to the meteorological journal (manuscript) 

 of M. Don Antonio Robredo, at the Havannah, the extreme 

 oscillations in 1801, were, in the maxima of the months 

 30.16 in (angl. measure), and 30.41 in j in the minima, 29.52 

 and 30.38. Difference of the maxima, 5.28 mm : of the mi- 

 nima, 18.20 mm . At Paris and Strasbourg the extreme as- 

 cending oscillations do not vary more in different months, 

 than from 10 to 12 millimeters j the extreme descending os- 

 cillations vary from 20 to 30 millimeters. 



+ Laplace, Essai Phil, sur les probability's, 1825, p. 11.9, 



