46 BULLETIN OP THE 



Mr. B. F. Craig, referring to the assumption that the exists 

 ence of large tracts of land near the equator had a decisive effect 

 in increasing the general warmth of the atmosphere, said that 

 air may rise to 120° Fah. over dry and barren land, and does 

 not rise much over 80' on the ocean, but a cubic yard of air 

 heated from 40° to 80° by contact with warm water takes up as 

 much as (50) fifty heat-units (English), of which thirty-two be- 

 long to the water vaporized. When the air is again cooled to 40° 

 the vapor is condensed, and the whole fifty units are given off. 



A cubic yard heated from 40' to 120' over a dry surface takes 

 up only thirty-four units, notwithstanding the higher temperature 

 attained. 



A cubic yard of water heated to 40° takes up (67,000) sixty- 

 seven thousand units. 



The deposition of moisture from air is a more important means 

 in the distribution of heat than the convection by the air pro- 

 per ; and the supposed existence of large tracts of land about the 

 equator will be far from conveying the effect which Mr Lyell 

 and others have supposed, in giving us a warmer climate. The 

 conditions, therefore, which seemed more favorable for the exist- 

 ence of a tropical climate near the poles would be a large equa- 

 torial ocean, and such a formation of the continents as to draw 

 the currents of the ocean toward one particular pole. 



Mr. Taylor, replying to Mr. Dutton, said that the present 

 issue, concisely stated, appeared to be, that, while one side would 

 impugn the sufficiency of the "astronomical" theory, the other 

 disputed the verity of the "geographical." Mr. T. thought that 

 one great merit of Mr. Croll's hypothesis was that it seemed to 

 explain a large number of varied, yet correlated, results, cumu- 

 lative in their effect — from the gradual action of apparently very 

 small differences as causes. In this it harmonizes admirably 

 with the "uniformitarianism" which forms the basis of all our 

 scientific investigations and theories. 



In regard to the thermal equator, which is now on the average 

 a few degrees north of the geodetic equator, it is true, as Mr. 

 Dutton has remarked, that it is greatly influenced by geographi- 

 cal arrangement. But any conditions which would change the 

 relative force of the northeastern and the southeastern sets of 



