INTRODUCTION. 18 



will here limit myself to the consideration of a few of the 

 general results whose combination constitutes the physical 

 delineation of the torrid zone. That which, in the vagueness 

 of our impressions, loses all distinctness of form, like some 

 distant mountain shrouded from view by a veil of mist, is 

 clearly revealed by the light of mind, which by its scrutiny 

 into the .causes of phenomena learns to resolve and analyze 

 their different elements, assigning to each its individual cha- 

 racter. Thus in the sphere of natural investigation, as in 

 poetry and painting, the delineation of that which appeals 

 most strongly to the imagination, derives its collective interest 

 from the vivid truthfulness with which the individual features 

 are pourtrayed. 



The regions of the torrid zone not only give rise to the 

 most powerful impressions by their organic richness and their 

 abundant fertility, but they likewise afford the inestimable 

 advantage of revealing to man, by the uniformity of the varia- 

 tions of the atmosphere and the development of vital forces, 

 and by the contrasts of climate and vegetation exhibited at 

 different elevations, the invariability of the laws that regulate 

 the course of the heavenly bodies, reflected, as it were, in 

 terrestrial phenomena. Let us dwell then for a few moments 

 on the proofs of this regularity, which is such, that it may be 

 submitted to numerical calculation and computation. 



In the burning plains that rise but little above the level 

 of the sea, reign the families of the banana, the cycas, and 

 the palm, of which the number of species comprised in the 

 flora of tropical regions has been so wonderfully increased in 

 the present day, by the zeal of botanical travellers. To these 

 groups succeed, in the Alpine valleys and the humid and 

 shaded clefts on the slopes of the Cordilleras, the tree-ferns, 

 whose thick cylindrical trunks and delicate lacelike foliage 

 stand out in bold relief against the azure of the sky, and the 

 cinchona, from which we derive the febrifuge bark. The 

 medicinal strength of this bark is said to increase in propor- 

 tion to the degree of moisture imparted to the foliage of the 

 tree by the light mists which form the upper surface of the 

 clouds resting over the plains. Everywhere around, the con 

 fines of the forest are encircled by broad bands of social 

 plants, as the delicate aralia, the thibaudia and the myrtle- 

 leaved andromeda, whilst the Alpine rose, the magnificent 



