246 Temperature of the Atmosphere 



all classes of organised matter. It is by the means of this 

 wonderful agent that we gain the theory of respiration in 

 all classes of creatures possessing animal life ; it is by this 

 agent that we become acquainted with the migrations of ani- 

 mals, as well as of many of their peculiar instincts and habits. 

 It is the atmosphere that enables us to account for the peri- 

 odical changes in the plumage of birds, and the furs of ani- 

 mals, and also the variety of colours to be found amongst 

 them. It is by means of the elasticity of the atmosphere, 

 too, that sounds and odours are transmitted to sensitive beings. 

 As this fluid, therefore, is the most essential of all the elements 

 to the support and continuance both of animal and vegetable 

 life, it certainly deserves the most serious attention of every 

 rational being. 



The atmosphere, agreeably to certain laws of nature, and 

 the benevolent skill which the Author of nature has displayed 

 in the formation of so surprising a fluid, varies in its temper- 

 ature in different regions of the earth ; and this variation is 

 attributable to various causes, which cannot fail to attract the 

 serious attention of every lover of nature ; and the enquiry 

 becomes still more interesting when its effects upon the animal 

 and vegetable kingdoms are considered, as they lie dispersed 

 over every part of the globe. Had a uniform climate been 

 established over the face of the whole earth, we should have 

 been deprived of that beautiful variety of plants and animals 

 which now strikes us with astonishment at every step. 



As the word climate, according to its Greek import, signi- 

 fies to incline, or to slope, it was probably first adopted by the 

 ancient geographers to denote the different inclination at which 

 the rays of the sun fell upon the surface of the earth, and 

 which they restricted to certain belts of the earth's surface, 

 beginning at the equator, and proceeding towards the poles. 

 The distinction between one of these belts and another, or one 

 climate and another, was a difference of half an hour in the 

 length of the longest day. According to this division of the 

 earth's surface into climates, the difference of temperature and 

 the difference of the length of the longest days lost all propor- 

 tion, for it was soon discovered that the breadth of the first 

 climate, i.e. the one nearest to the equator, measured 295 miles, 

 while the twenty-second climate, or that in the northern part 

 of England, measured less than 70 miles. However satisfac- 

 tory this division of the earth's surface might be, to show the 

 inclination of the solar rays; it did not in any degree point 

 out how far the climates of these diflerent latitudes were favour- 

 able or unfavourable to animal and vegetable existence. 



