699 



question, in the present state of our knowledge 

 cannot be completely solved. We know gene- 

 rally only the apparent, and not the real 

 epochas ; even the former are not always indi- 

 cated with sufficient precision. Travellers have 

 observed the maxima and the minima, as it 

 were by chance, sometimes at the moment 

 when the limits were attained, sometimes an 

 hour later, and while the barometer was in a 

 stationary state. The numerous observations 

 of M. Ramond prove that, in the temperate 

 zone, in 45° and 46° of latitude, the tropical 

 hours, or limit-hours, change from summer to 

 winter, and that the two points of the diurnal 

 maximum and minimum, draw nearer noon in 

 proportion as the cold augments*. We are 

 yet ignorant whether similar changes do not pre- 

 cede, in a part of the torrid zone, (at Quito and 

 Bombay, for instance,) the epocha when, under 

 the influence of local circumstances, in the 

 rainy season, it is said, that the regular type of 

 the horary variations has altogether disap- 

 peared. We cannot too much recommend this 

 point to the researches of travellers. I shall 

 here note what I have hitherto collected with 

 most certainty on the epocha of the maxima 

 and the minima. 



* Mem. de VInst., 1808, p. 103, (Bibl. Universelte, 

 Fevrier, 1824, p, 93.) 



