THE ADVANCE OF SCIENCE 81 



surface. The geologists and the biologists have long 

 contended that some thousand million years must have 

 passed during which the earth's surface has presented 

 approximately the same conditions of temperature as at 

 present, in order to allow time for the evolution of living 

 things and the formation of the aqueous deposits of the 

 earth's crust. The physicists, notably Professor Tait 

 and Lord Kelvin, refused to allow more than ten million 

 years (which they subsequently increased to a hundred 

 million) basing this estimate on the rate of cooling of 

 a sphere of the size and composition of the earth. They 

 have assumed that its material is self-cooling. But, as 

 Huxley pointed out, mathematics will not give a true 

 result when applied to erroneous data. It has now, 

 within these last five years, become evident that the 

 earth's material is not self-cooling, but on the contrary 

 self-heating. And away go the restrictions imposed by 

 physicists on geological time. . They now are willing to 

 give us not merely a thousand million years, but as many 

 more as we want. 



And now I have to mention the strangest of all the 

 proceedings of radium a proceeding in which the other 

 radio-active bodies, actinium and thorium, resemble it. 

 This proceeding has been entirely Rutherford's discovery 

 in Canada, and his name must be always associated with 

 it. Radium (he discovered) is continually giving off, 

 apart from and in addition to the rectilinear darting 

 rays of Becquerel an ' emanation ' a gaseous * emana- 

 tion.' This ' emanation ' is radio-active that is, gives 

 off Becquerel rays and deposits 'something' upon bodies 

 brought near the radium so that they become radio- 

 active, and remain so for a time after the radium is 

 itself removed. This emanation is always being formed 

 by a radium salt, and may be most easily collected by 



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