704 



In comparing the hours of the maxima and 

 the minima in different zones, we must not con- 

 found the observations that are made in cir- 

 cumstances altogether different. We must dis- 

 tinguish the places where, during the whole 

 year, in the time of drought, as well as of rains, 

 the barometer furnishes a regular periodic 

 movement ; and the places where, during the 

 rainy season and monsoons, this movement is 

 interrupted or rendered insensible. According to 

 Thibault de Chanvalon, the influence of these 

 causes is not observed* at Martinique; I re- 

 marked it on the continent of Spanish America, 

 only at Quito, in the month of April, and at 

 Vera Cruz, when the north wind blows with the 

 greatest violence. Dr. Cassan asserts, that he 

 found great irregularity in the island of Saint 

 Lucia, south of Martinique. " We have ob- 

 served," he says-jr, " with great care the famous 

 variation of the barometer, which is indepen- 

 dent of the apparent constitution of the atmos- 

 phere, and has been celebrated by Godin and 

 Chanvalon. The periodical movement of as- 

 cension and lowering, takes place, no doubt,, 

 twice in twenty-four hours ; but the hour of 

 the movement appeared to me much less regu- 

 lated than is pretended." This assertion of Dr» 



* Voyage a la Martinique, p. 135 (2S)\ 



t Journal de Phijs., 1790, Tom. 36, p; 208. 



