Variations- of the Barometer. 



293 



my departure for America, I had obtained a knowledge of 

 the regularity of the horary movements of the barometer. * 

 Doctor Mosely, in his Treatise on Tropical Diseases, pub- 

 lished in 1792, observe?, that the barometer has two daily 

 movements, one of ascent, and the other of descent, rising 

 when the sun approaches the zenith or nadir, and falling 

 when he recedes from these paints. Dr Balfour also observed 

 the barometrical changes for every half hour, during a whole 

 lunation, in the year 1794. 



I commenced the series of my observations on the varia- 

 tions of the weight of the atmosphere, along with M. Bon- 

 pland, on the 18th July 1799, two days after our arrival at 

 Cumana, and I continued them for five years with the 

 greatest care, from 12° of south lat., to 23° of north lat., 

 in the plains and on the table lands, whose height is equal to 

 the peak of Teneriffe. Since the time of my voyage to the 

 Equator, this phenomenon has occupied almost all travellers 

 and natural philosophers, who have been provided with instru- 

 ments fitted for making these observations. 



As our limits will not permit us to follow our author 

 through the details of his elaborate dissertation, we shall now 

 present our readers with two of the latest and most accurate 

 sets of observation on the horary changes of the barometer 

 made within the tropics, the first by Captain Freycinet in 1820, 

 and the second by M. Duperry in 1823. 



* See tliis Journal, No. iv. p. 336. 



