757 



I have added in the preceding* pages a great 

 number of unpublished materials to those dis- 

 persed in different works. I shall conclude 

 this task by indicating the laws, or rather 

 the most general relations, which the singular 

 phenomenon of the small atmospheric tides 

 presents : 



1° The horary oscillations of the barometer 

 are felt in every part of the earth, in the torrid, 

 as well as in the temperate and frigid zones, at 

 the level of the sea as well as at elevations ex- 

 ceeding 2000 toises. These oscillations are 

 periodical, and every where composed of two 

 ascending and descending movements. The 

 two atmospheric tides are not in general of 

 equal duration *. In comparing results of un- 

 equal exactness, and obtained by thirty obser- 

 vers, between 25° of south latitude and 55 Q of 

 north, we find differences of 2 hours for the 

 epochas of the maxima and the minima : in ex- 

 cluding five results only, the maximum of the 

 morning falls between Si h and I0h h ; the mini- 

 mum afternoon, between 3 h and 5 h ; the maxi- 

 mum of the evening between 9 h and \\\% and 

 the minimum between 3 h and 5 h in the morn- 

 ing. It is to be presumed that those limits will 

 be found to be drawn much nearer when a 



* See the Table of the general statement of tlie horar?j ob~ 

 strvations. The result most generally is, for the duration of 

 the ascending and descending tides,, between the tropics, 

 6l h , 6*, 6 h , and 5§ h . 



