348 J. Croll—Professor Newcoml’s “ Rejoinder.” 
stated, what every physicist knows to be perfectly correct, that 
the aqueous vapor of the air radiates back a portion of its 
heat; and the ocean, for reasons which have been already 
stated, absorbs this radiation more freely than the land. Radi . 
ation from 1 
each other by their mutual radiation. This is not the state of 
the case at all, for both bodies receive their heat from the sun ; 
their mutual radiation simply retains them at a higher tempera- 
ture than they could otherwise have. Here Professor Newcom 
appears to get into confusion owing to the meaning which he 
attributes to the word “heating.” The views which I have 
advocated in reference to this mutual radiation are as follows: 
According to the dynamical theory of heat, all bodies above 
absolute zero radiate heat. If we have two bodies, A at 200 
and B at 400°, then, according to Prevost’s theory of exchanges, 
A as truly radiates heat to B as B does to A. The radiation 
of A, of course, can never raise the temperature of B above 
400° ; but nevertheless the éendency of the radiation of A, in 80 
far as it goes, is to raise the temperature of B. This is demon- 
strated by the fact that the temperature of B, in consequence 
of the radiation of A, is prevented from sinking so low as It 
would otherwise do. All this is so well known to every stu 
dent of thermodynamics, that I can hardly think Professor 
In bis Review of ‘Climate and Time,’ Professor Newcomb : 
advocated, as a fatal objection to my theory, that the pape: | 
my reply (this Journal, Oct., 1883, p. 264), is based _—— 
* Were this objection correct it would prove that there could have aoe 
Glacial Epoch; for it is obvious that had not the sun’s heat failed to melt pee 
winters snow, not during the course of a few days merely but during the enure” - 
summer, there could not possibly have been permanent ice. 
my 
