160 Proceedings of the Royal Physical Society. 



II. On the Geographical Distribution of the Marine Invertebrata in 

 past time, considered in relation to the Doctrine of the Secular 

 Cooling of the Earth. By Andrew Taylor, Esq. 



The doctrine of the secular cooling of the earth has again 

 been prominently brought before the scientific public, by 

 two ingenious calculations regarding the time required for 

 such a phenomenon to take place. 



Professor Haughton of Dublin demands 1018 millions of 

 years for the earth to cool down from 212° F. to 122° F. ; 

 the latter temperature being supposed the one at which the 

 waters became habitable. He moreover demands the farther 

 period of 1280 millions of years for the cooling from 122° F. 

 to 77° F. ; a period comprising the whole time from the first 

 appearance of life in the earth to the latest Eocene epoch. 

 If such decided physical changes have occurred during the 

 period from the appearance of life on the globe to the dawn 

 of the present creation, they must have influenced very de- 

 cidedly the succession and distribution of life in the geologic 

 eras. 



If such calculations can be ranked amongst the ascer- 

 tained facts of science, biological speculations founded on 

 them will likewise pass from hypothetical probabilities into 

 scientific deductions. 



That they are far from this, however, may be seen by 

 alluding to Professor William Thomson's calculations on 

 this subject : he fixes the time required for the whole period 

 of the earth's crust from a state of fusion to its present 

 condition, at 98 millions of years, and therefore allows only 

 100 millions of years for all speculations regarding the 

 earth in its solid state. Experimental data are adduced 

 in support of his assertions. Such are the widely discre- 

 pant results attained by two eminent savans. Do they not 

 throw great uncertainty on the whole subject ? 



Notwithstanding, it may not be unphilosophical to inves- 

 tigate the appearance and distribution of life in geologic 

 times, on the assumption that this hypothesis is an ascer- 

 tained physical fact. 



