150 Objects and Uses of Metewology, 



by an unseen and mysterious energy operating within them ; 

 but organised beings depend, for the outward support of 

 their existence, or rather for the preservation of the substances 

 on which their organisation is founded, in a fit condition for 

 the use of the inward powers of life, on the heat and hght of 

 the sun. And in a mediate manner, therefore, they depend 

 on the atmosphere, which is the medium by which the rays 

 of that glorious luminary are accommodated to their reception. 

 Hence they are distributed over the surface of the globe, with 

 relation to the peculiar qualities of every class, according to 

 certain laws by which we are accustomed to express the 

 phaenomena of climate^ and which are regulated, chiefly, by the 

 relations to heat or temperature of the parts of the earth re- 

 spectivelly inhabited by each group of animals or plants. 

 These relations to temperature are of two kinds. The first 

 depends on the position of the locality, or place where the 

 beings naturally exist, with respect to the equator, or rather 

 to the ecliptic, or, more strictly still, with'respect to the plane 

 in which the earth revolves around the sun ; for on this rela- 

 tion depends the temperature of the place, so far as it is pro- 

 duced, directly, by the influence of the sun. The second of 

 these relations to heat depends on the elevation of the locality 

 above the mean level of the earth's surface, — usually esti- 

 mated, for the purposes of science, from the level of the ocean, 

 — for on this depends another cause of difference of tem- 

 perature, in consequence of the decrease of density, as we 

 ascend in the atmosphere, and the corresponding reduction of 

 temperature by the increased capacity for heat of rare air; 

 the highest situations being the coldest in each latitude 

 respectively. 



According, then, to the laws of temperature, arising from 

 the combined influence of latitude and altitude, as just ex- 

 plained, are the innumerable subjects of organised nature 

 distributed throughout the globe, whetlier the land, the 

 waters, or the atmosphere be the principal scene of their 

 existence. Next to the solar beams, as an agent in the sup- 

 port of life, in all its various forms, is moisture, which appears 

 indeed to operate as a medium, in conveying and imparting to 

 the solid substances of organisation the influence of the im- 

 ponderable agents, as heat, light, and electricity, as well as 

 that of the vital energy itself. And the state of moisture 

 depending primarily on the presence of aqueous vapour, its 

 quantity and its tension or elasticity is of course finally de- 

 pendent on temperature and on the agency of solar radiation. 

 Certain plants and animals are peculiar, as is well known, to 

 the tropical regions, where an unvarying high degree of heat 



