CLIMATOLOGY. 313 



parency of the air and serenity of the sky, which has an 

 important influence not only on the organic development of 

 plants and the ripening of fruits, but also on the feelings 

 and the whole mental disposition of man. 



If the whole surface of the earth consisted either of a 

 homogeneous fluid mass, or of strata of rock perfectly alike 

 in colour, density, and smoothness, and of equal capacity 

 both for the absorption of the sun's rays, and for radiat ing 

 heat through the atmosphere into space, the isothermal; 

 isotheral, and isochimenal lines would all be parallel to the 

 equator. In this hypothetical condition of the earth's 

 surface, the power of absorption and emission of light and 

 heat would, under equal latitudes, be every where the same. 

 From this mean, and, as it were, primitive condition, which 

 neither excludes currents of heat in the interior of the globe 

 or in its external covering, nor the propagation of heat 

 by atmospheric currents, the mathematical consideration of 

 climate proceeds. Whatever alters the power of absorption 

 and of radiation, in any of the several parts of the earth's 

 surface under the same parallel of latitude, causes inflections 

 in the isothermal lines. 



The progress of climatology has been remarkably favoured 

 by the circumstance that European civilisation has extended 

 over two opposite coasts, having passed from our western 

 shores to a coast on the other side of the Atlantic valley having 

 an eastern aspect. When, after the ephemeral colonisation 

 from Iceland and Greenland, the British formed the first 

 permanent settlements on the coast of the United States of 

 America, and the colonists (whose numbers were rapidly 

 augmented by the effects of religious persecution, fanaticism, 



