THE GEOLOGIST. 



JANUARY 1864. 



ON THE EARTH'S CLIMATE IN ANCIENT TIMES. 

 Br the Editor. 



Foe, some time past we have been drawing attention to some of the 

 dicta of Geology, which appear to have a less solid foundation than 

 they should have to authorize the positive manner in which they have 

 been enunciated. Similar doubts on some points would appear not 

 to be absent from other minds. Mr. Page has just issued a little 

 work reviewing the state of the popular doctrines of our science, and 

 Mr. Sterry Hunt has appropriated to the explanation of the higher 

 Palaeozoic climate Dr. TyndalPs memorable researches on the rela- 

 tions of gases and vapours to radiant heat. Heat, from whatever 

 source it may proceed, passes through hydrogen, oxygen, and nitrogen 

 gases and dry air, with nearly the same facility as through a vacuum, 

 and these gases are thus. to radiant heat what rock-salt is amongst 

 solids. Glass and some other substances which are readily per- 

 meable to light and to solar heat, offer, as is well known, great ob- 

 stacles to the passage of radiant heat from non-luminous bodies, and 

 many vapours and gases have a similar effect in intercepting the heat 

 from such sources. Thus, for a vacuum the absorption of heat from a 

 body at 212° Eahr. is represented by 0, that by dry air as 1, while the 

 absorption by an atmosphere of carbonic acid gas is 90 ; by one of 

 marsh-gas, 403 ; by olefiant gas, 970; and by ammonia, 1195. Ole- 

 fiant gas at 1 inch tension produces an absorption of 90°, and car- 

 bonic acid gas in the same state, an absorption of 5 6. The small 

 quantities of ozone present in electrolytic oxygen were found to raise 



VOL. VII. B 



