HEAT. 713 



climates has been elucidated by the calculations of Mr. James Croll. 

 His conclusion is, that the amount of heat conveyed from the equa- 

 torial regions northward in the Atlantic by this stream is equivalent 

 to 77,479,650,000,000,000,000 foot-pounds of energy per day, which 

 is equal to all the heat received by 1,560,935 square miles at the 

 equator, and more heat than is conveyed by all the aerial currents ; 

 and that the stoppage or diversion of the current would diminish to 

 this extent the heat of the Arctic seas and North Atlantic. (Croll's 

 Climate and Time, p. 25.) 



It has been supposed that the diversion of the Gulf Stream from the 

 North Atlantic may have taken place through the sinking of the region 

 of the Straits of Darien ; but there is no sufficient evidence that such 

 a diversion has happened since Mesozoic time, if it did before. A 

 more reasonable hypothesis is that it may have been accomplished by 

 a raising of the sea-bottom nearly to the surface between Scandi- 

 navia, Great Britain, Iceland, and Greenland, where the depth now 

 is mostly less than 100 fathoms and nowhere exceeds 1,000, and 

 along one tract, is not over 500 fathoms. The effect of such a North 

 Atlantic barrier would be to confine the Gulf Stream circuit to the 

 North Atlantic, and thereby to increase the temperature and amount 

 of evaporation of that ocean. It would reduce the stream to the south- 

 east branch and might diminish its volume ; but, in view of the form 

 of the South Atlantic depression and its position with reference to the 

 North Atlantic, the warm stream could not fail to continue its flow. 



Again, the Arctic region, as F. H. Bradley has suggested, may 

 formerly have had its climate moderated by receiving the Pacific trop- 

 ical current, through a submergence about Behrings Straits — now 

 only 150 feet deep; and if so, this current, upon the opening of the 

 deep passage for discharge northward, would have been augmented in 

 its size and its heating influeuce. 



Changes in the distribution of climate have been attributed to as- 

 sumed changes in the position of the earth's axis of rotation. But 

 mathematical investigations by Sir Wm. Thomson, Professor Haugh- 

 ton, Mr. George H. Darwin and others, have shown the hypothesis to 

 be of no geological value. Mr. Darwin has demonstrated that a dis- 

 placement of the pole of merely 1° 46 ; would require that a twentieth 

 of the whole earth's surface should be elevated to a height of 10,000 

 feet, with a corresponding subsidence in another quadrant ; and for 

 one of 3° 17', that double the surface should have undergone these 

 great changes. Sir Wm. Thomson concludes from his discussion of 

 the subject that " there is no evidence in geological climate throughout 

 those parts of the world which geological investigation has reached to 

 give any indication of the poles having been anywhere but where they 

 are at any period of geological time." 



