MODERN SCIENCE. 163 



chart of the earth, ISOTHERMAL LINES (lines of equal heat), 

 which indicate for all places a given mean temperature for 

 the year. Isothermal lines for the year are called annual 

 isotherms : the isotherms for July and January are respectively 

 called isotherals (summer) and isocheimenals (winter). 

 These charts are most important aids to the study of 

 climatology, " indicating as they do those general laws which 

 apart from latitude and altitude affect the climate of a 

 country. The winter isotherms which cross the British 

 Isles offer a striking feature : they run nearly North and 

 South across Britain instead of lying along parallels of lati- 

 tude; so that a high temperature is to be sought by travelling 

 from East to West instead of North to South." Since 

 Humboldt's time this branch of science has rapidly advanced. 

 One of the chief facts ascertained which affects the economy 

 of a country is the action of aqueous vapour in checking 

 (I.) the radiation (loss of heat) of the earth's heat into space, 

 and (n.) the fierceness of the sun's heat on the earth, owing 

 to the power of aqueous vapour to absorb and retain heat. 

 Says Tyndall on the subject : " Aqueous vapour is a blanket 

 more necessary to the vegetable life of England than clothing 

 is to man. Remove for a single summer night the aqueous 

 vapour from the air which overspreads the country, and you 

 would destroy every plant capable of being destroyed by a 

 freezing temperature." And conversely, if the aqueous vapour 

 did not absorb and retain a great portion of the sun's heat 

 in summer, the vegetation would be parched up, and animals 

 would die from the effects of heat. Climate is affected also 

 by altitude, by proximity of large masses of water, evaporation, 

 and sea and wind currehts. 



1774 1853. Buch (L. Von) demonstrated the great 

 mountain ranges to have been covered by the sea, but to have 

 been formed by gradual upheavals ; discovered the slow and 

 gradual elevation of Sweden, but failed to detect volcanic 

 agency in new formations. As a naturalist he observed the 

 Fauna of the Canaries, and he pointed out that varieties may 

 be slowly changed into permanent species, thereby antici- 

 pating Darwin in one point. 



< Ritter (Carl) created COMPARATIVE GEOLOGY 



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