"$% M. Humboldt on the Horary 



horary variations of the barometer, which he had observed 

 at the Antilles. In a work published in 1761, he observes, 

 " that, a short time after his arrival in Martinique, he per- 

 ceived that the barometer rose gradually during the whole 

 morning, and that, after it had been some time in motion, it 

 began to descend till sunset. After having been some time 

 stationary, it rose at the approach of night, till ten in the 

 evening. The most considerable revolutions in the atmo- 

 sphere do not alter this periodical march of the barometer, 

 which coincides with that of the horary variations of the mag- 

 netic needle. In the middle of the most copious rains, of winds 

 and of storms, the mercury rises and descends, if it is its time 

 to rise or descend, as if all was tranquil in the air. The same 

 variations take place at Senegal." 



Since the year I76I, Doctor Mutis has observed the at- 

 mospherical tides at St a Fe de Bogota during forty years. He 

 determined, with precision, the epoch of the minimum which 

 precedes sunrise ; but, unfortunately, his observations, which 

 he concealed with too much care during his life, have not 

 been published since his death. M. Mutis in New Granada, 

 Alzate and Gama in Mexico, were the first who examined the 

 hourly variations on the back of the Cordilleras at 1200 and 

 1400 toises above the level of the sea. 



Neither the observations of Thibault de Chauvelon in 1751, 

 nor the small number of those published by Alzate in 1769, 

 corresponded to the tropical hours, that is, to the epochs when 

 the barometer arrives at the convex and concave summits of 

 the curve of its daily variations. It was in the voyage of La 

 Perouse, that MM. Lamanen and Mongez made, in 1785, 

 every hour the first continuous observations, during three 

 days and three nights, when they were in the middle of the 

 Atlantic Ocean, between the parallels of 1° north latitude, and 

 1° south latitude. 



The work of Lamanon is anterior, by eight years, to that 

 undertaken at Calcutta by Messrs Trail, Farquhar, Pierce, 

 and Balfour ; but, as their results were inserted in the fourth 

 volume of the Asiatic Researches, published at Calcutta in 

 1795, while the voyage of La Perouse did not appear till 

 1797, the Indian observations acquired more celebrity in 

 Europe. They were, indeed, the only ones from which, at 



