l\ :. Fiankland on tkt P ■'. C 



already quoted, and he has conclusively shown it to be quite 

 untenable on astronomical grounds, T... second requires some 

 consideration, since it is by no means improbable that the sun 

 was once a more active radiator of heat than he is at present, 

 although the assumption that this should have been the case to 

 a marked extent so recently as the ;: the glacial epoch is 



... highest I: might be anticipated that 



an augmentation ei solai old increase the I imperature 



of the oceanic surface, and probably not interfere much with the 

 functions of the radiating condenser, the luminous heat-rays of 

 the sun not having yet been proved :: be much absorbed by 



leoos vapour. But :: would lonbtless gi eatly impair the effi- 

 ciency of the ice-bearers, "hose powerfully absorbent sad 

 would, under increased solar radiation, be less able to maintain 

 the necessary Low temperature. I :i:..i. : :i.;\ however, :: is not 

 m itisary to rely ug : 11 . i . jture in this mattei . for the denion- 

 stration is constantly lefore us, in the comparative effects :: solar 

 radiation upon glacial phenomena in the different terrestrial 

 zones. The solar radiation within the tropica is augmented as 

 compared with thai :i the tern] .1 ate and frigid rones, but this 

 augmentation does no: bring 1 a glacial epoch in the torrid 

 zone ; on the contrary, although the snow-line is. as above stated, 

 depressed as regards the line of 32° 3 ye: both are irresistibly 

 driven up the mountains. 



Thus no cosmical source 11 heat is ::.. stent to produce the 

 phenomena of the glacial epoch, and there remains therefore only 

 the well-kn 1 ~ 01 secular source — the internal heat of the earth. 

 Fhe problem if the influence 1: he earth's internal heat upon 

 the surface temperature has leen most ably iiseussed by Mr. 

 Hopkins* and Professor W. Tromsont. Taking the result of 

 Poisson's calculation, that the part 1: the earth 3 1 ssent super- 

 ficial temperature due to primitive heat amount* :. 1 11 >.- one- 

 twentieth of a degree Fahi 11: "....:. Professoi Hopkins | roves that 

 the augmentation of surface temperature from this cause :i the 

 exten: of 10 : F. would involve a descending rate :. inci ase bo 

 rapid as to re: P. at s lepth if :__> B( feet, — a physical 



condition of our planet which would, as he remarks, si 1 aely ; 

 stent with the condition- 1 animal life .: the more recent 

 geological epoch?. Assuming Poisson's datum - .: nrrect, 

 this result is probably indisputable,, as pplied fa the solid sur- 

 face of our pi an t it is not necessarily when exf ended 

 to the floor of the ocean. Indeed there are some considerations 

 resrarding the transmission of heat through a thick stratum of 

 water, which appear to me to render this calculation total".; in- 



* Joum. FGeoL. Soc 56 I PhiL Frans. 1857, p. 805. 



+ Transactions of the Royal Society of E diubuig h, * . mn. ; I : " 



