Variations of the Barometer. 299 



of the extreme monthly oscillations are, in tne ascending mo- 

 tion, one-half nearer each other than under the tropic of Can- 

 cer. In the limits of the ascending oscillations, this difference 

 between the two zones is much less sensible. The interrup- 

 tion of the horary oscillations presents, near the tropic of Can- 

 cer (in the Gulf of Mexico) a prognostic of the proximity of 

 tempests, of their force and their duration. The monthly 

 means of the barometric heights diminish regularly, from July 

 to December and January, on the plain of Bogota, and even 

 in the southern hemisphere, on the coast of Rio Janeiro. At 

 the extremity of the northern equinoctial zone, the return of 

 the north winds raises the means of December and January 

 above those of July and August. 



9. Under the tropics, as in the tempei-ate zone, in compar- 

 ing the extreme deviations of the barometer, month by month, 

 we find the limits of the ascending oscillations two or three 

 times nearer than the limits of the descending oscillations. 



10. The observations hitherto collected do not indicate any 

 sensible influence of the moon on the oscillations of the atmo- 

 sphere. These oscillations appear to be owing to the sun, 

 who acts not by his mass, viz. by attraction, but as a star, ra- 

 diating heat. If, in modifying the temperature, the Solar 

 rays produce periodical changes in the atmosphere, it remains 

 to be explained why the two barometric maxima coincide al- 

 most with the warmest and the coldest epochs of the day and 

 the night. 



The following table will afford a general view of all the 

 horary results : 



