ADI)UE8S. 23 



The uccan is a groat ccjualiser of extremes of torapcraturo. It does 

 tills by its great capacity for heat and by its cooling and heating power 

 when paHsing from the solid into the li((uid and gaseous status, and the 

 reverse. It also acts by its mobility, its currents serving to convey heat 

 to great distances or to cool the air by the movement of cold icy waters. 

 The land on the other hand coola or warms rapidly, and can transmit its 

 influence to a distance only by the winds, and the influence so transmitted 

 is rather in the nature of a disturbing than of an ecinalising cause. It 

 follows that any change in the distribution of land and water must aflect 

 climate, more especially if it changes the character or course of the ocean 

 currents.* 



At the present time the North Atlantic presents some very pecnliar 

 and in some respects exceptional features, whicli are most instructive with 

 reference to its past history. The great internal plateau of the American 

 continent is now dr ' land ; the passage across Central America between 

 the Atlantic and Pacific is blocked ; the Atlantic opens very widely to the 

 north ; the high mass of Greenland towers in its northern part. The 

 effects are that the great equatorial current running across from Africa and 

 embayed in the Gulf of Mexico, is thrown northward and eastward in the 

 Gulf Stream, acting as a hot water apparatus to heat up to an exceptional 

 degree the westorn coast of Europe. On the other hand, the cold Arctic 

 current from the polar seas is thrown to the westward, and runs down 

 from Greenland past the American shore.^ The pilot chart for June of 

 this year shows vast fields of drift ice on the western side of the Atlantic 

 as far south as the latitude of 40°. So far, therefore, the Glacial age in that 

 part of the Atlantic still extends ; this at a time when, on the eastern 

 side of the Atlantic, the culture of cereals reaches in Norway beyond the 

 Arctic Circle. Let us inquire into some of the details of these phenomena. 



The warm water thrown into the North Atlantic not only increases 

 the temperature of its whole waters, but gives an exceptionally mild 

 climate to Western Europe. Still the countervailing influence of the 



succession of cold and warm climates in the northern hemisphere, enumerates no 

 fewer than seven theories which have met with more or less acceptance. These are : — 



1. The gradual cooling of ti.e earth from a condition of original incandescence. 



2. Changes in the obliquity of the ecliptic. 



3.' Changes in the position of the earth's axis of rotation. 



4. The effect of the precession of the equinoxes along with changes of the eccen- 

 tricity of the earth's orbit. 



5. Variations in the amount of heat given off by the sun. 



6. Dififerences in the temperature of portions of space passed through by the 

 earth. 



7. Differences in the distribution of land and water iu connection with the flow 

 of oceanic currents. 



' Von Woeickoff has very strongly put these principles in a Review of Croll's 

 recent book, Climate and Cosvwlogy ; American Journal of Sdence, March 1886, 



' I may refer bcre to the admirable expositions of these effects by the late 

 Dr. Carpenter, in hia papers on the results of the explorations of the Challenger. 



