24 president's address. 



than the simpler hypothesis of Professor Darwin.* According 

 to Professor Chamberlin, the accretion of planetoids was in all 

 probability a slow process, so much so that the heat of impact 

 was dissipated about as rapidly as acquired. Hence, he concludes, 

 conditions suitable for the establishment of life may have existed 

 when the earth was but a fraction of its present size. The 

 existence of central high temperature he attributes in part to a 

 remnant of gravitational heat acquired through the primary 

 nucleus having been gathered rapidly when planetoids were 

 relatively abundant, but in the main to the gradual increase in 

 pressure as the globe increased in size. Mere pressure does not 

 produce heat unless it causes change of volume, and it seems 

 doubtful to me that the denser packing and molecular rearrange- 

 ment through increase in pressure, which Professor Chamberlin 

 assumes, could be sufficient to generate the heat required. He, 

 however, expressly states his conviction of the sufficiency of the 

 cause given, and conclvides that the present internal temperature 

 of the earth increases steadily to the centre, which he estimates 

 to be about 20,000'C.(about 36,000° F.). It will be seen that 

 this tempeiature is greatly in excess of the 7,000° F w^iich Lord 

 Kelvin considers jiossible for the present surface thermal gradient 

 if due to a cooling hot centre, and still more in excess of the 

 modest 2,700° F. required by Mr. Strutt for a radium-warmed 

 globe. 



It is further not at all clear to me how under the conditions 

 postulated by Professor Chamberlin the lunar satellite could 

 come into existence. Professor Darwin concludes that the heat 

 of impact of the planetoids was great enough to cause incandes- 

 cence of the entire mass of the growing earth, and, as the result 

 of a careful mathematical examination of the problem of a 

 revolving molten mass such as is assumed for the early condition 

 of the earth, finds that the shape acquired will vary with the rate 

 of revolution. At one particular speed it will be of the earth's 

 present shape; at a higher speed the equatorial outline will be an 



Chamberlin & Salisbury, Geology, Vol.ii. 91, 1906. 



