Variations of the Barometer. 297 



+ 21 h £ ; — 4 h , -f. 10i h ; — I6 h , and for the temperate zone, 

 + 20£ h ; — Z\; + 9| ; — 17 h , astronomical time reckoned 

 from noon. 



2. In the temperate zone, the epochs of the maximum of 

 the morning, and the minimum of the evening, are nearer, by 

 l h or 2 h , the sun's passage of the meridian in winter than in 

 summer ; but the type of the summer resembles more the type 

 between the tropics. Observations on the morning minimum 

 are still much wanted. 



3. In the torrid zone, the times of maxima and minima 

 are the same at the level of the sea, and on the table lands 

 1300 or 1400 toises high. We are assured that this isochro- 

 nism does not show itself in some parts of the temperate zone, 

 and that, at the summit of the great St Bernard, the baro- 

 vaetevjhlls at the hours when it rises at Geneva. 



4. The variations everywhere become slower near the con- 

 cave and convex summits of the curve which represents them ; 

 and in some places the mercury seems to remain stationary, 

 during a time varying from 15' to 2 h . 



5. In general, under the torrid zone, between the equator 

 and the parallels of 15° north and south, the strongest winds, 

 storms and earthquakes, and the most sudden changes of tem- 

 perature and humidity, neither interrupt nor modify the re- 

 gularity of the horary variations. Whereas, in some parts of 

 equatorial Asia, as in India, where the monsoons blow with 

 violence, the season of the rains masks entirely the type of the 

 horary variations ; and, at the same time, when these varia- 

 tions are insensible in the interior of the continent, on the 

 coasts, and in straits, they show themselves, without any alte- 

 ration, in the open sea, under the same parallels. 



6. Between the tropics, a day and a night are sufficient to 

 determine the times of maxima and minima, and the dura- 

 tion of the small atmospherical tides. In the temperate zone, 

 in 44° and 48° of lat., the phenomena show themselves in all 

 seasons with much distinctness, in the means of from fifteen to 

 twenty days observations. 



7. The unequal extent of the diurnal variations produces, 

 in the torrid zone, at the same hours, in different months, 

 differences of barometrical height, more or less considerable. 



