CHAPTER II. 



MISAPPREHENSIONS REGARDING THE PHYSICAL THEORY 

 OF SECULAR CHANGES OF CLIMATE — REPLY TO CRITICS. 



Reason for considering Professor Newcomb's Objections. — Logical 

 Analysis rather than Mathematics required in the meantime.— 

 Temperature of Space. — Law of Dulong and Petit. — Heat Con- 

 veyed by Aerial Currents. — Why the Mean Temperature of the 

 Ocean ought to be greater than that of the Land. — Heat Cut Off 

 by the Atmosphere. 



Twenty-one years ago the theory was advanced that 

 the Glacial Epoch was the result of a combination of 

 physical agents brought into operation by an increase 

 in the eccentricity of the earth's orbit. Few or no 

 objections have been urged against what may be called 

 the astronomical part of the theory ; but the portions 

 relating to these physical agencies, which are by far 

 the most important part, have from time to time met 

 with considerable opposition. Considering the newness 

 of the subject, and the complex nature of many of 

 these combinations of physical agencies, it would not 

 be surprising if some of the original deductions in 

 regard to them proved erroneous ; but after long and 

 careful reconsideration of the whole matter, I have 

 not found reason to abandon any of them or alter 

 them to any material extent. 



The only class of objections urged against the 

 theory which I have as yet considered at length are 

 those relating to the cause of ocean-currents, and their 

 influence on the distribution of heat over the olobe ; 



C 



