January 29, 1915] 



SCIENCE 



157 



increasing interest in investigations of 

 safety problems peculiar to the industries 

 of each state. Their function has been to 

 investigate fundamental problems relating 

 to the efficient use of the material resources 

 of the state, but the change of emphasis 

 brought about by the safety movement will 

 make safety problems of equal moment. 



Another agency for the organized study 

 of safety problems is found in the banded 

 casualty insurance companies, who are in 

 a peculiarly favorable position to bring an 

 economic pressure to bear upon the indus- 

 tries to install standard, adequate safety 

 devices. They propose to offer a reduction 

 in rates where approved safety devices are 

 installed and the underwriters' laboratories 

 are hereafter to test approved safety de- 

 vices to reduce accident risks as well as de- 

 vices for reducing fire risks. 



The general government is also aiding in 

 safety engineering, as it is the province and 

 duty of the Federal Bureau of Mines to 

 conduct investigations with a view to in- 

 creasing safety in the mining, quarrying, 

 metallurgical and other mineral industries. 

 This is the first government bureau to be 

 established with the specific object of study- 

 ing industrial safety in fields other than 

 transportation. The laboratory facilities 

 include an equipped coal mine for the study 

 of mine explosions, chemical and physical 

 laboratories, and the new buildings about 

 to be commenced include mechanical and 

 electrical laboratories. 



These numerous agencies for the careful 

 study of safety problems, which lie just 

 behind the field of the self-evident and in 

 the land of the more or less obscure, will 

 each contribute something to the motley 

 interests of the safety engineer and wiU 

 help to eliminate industrial accidents. 



0. P. Hood 



U. S. BxjKEAU OP Mines 



ISOSTASY AND BADIOACTIVITYi 



It is the purpose of this paper to point 

 out some apparent discrepancies between 

 the observations of geodesists on isostasy 

 and the inferences which some radiologists 

 have drawn as to the great age of certain 

 specimens of minerals. It seems well to 

 begin by reviewing the results of isostatic 

 investigations in order to estimate the 

 degree of confidence to which they are en- 

 titled; and recent advances in radiology 

 demand similar attention. 



Correlation of these widely distinct re- 

 searches is possible because it happens that 

 the emission of heat by a globe whose excess 

 temperature is due solely to radioactivity 

 obeys Fourier's law exactly as does that 

 emitted by a hot but radioinactive globe. 



Geology as a science is conditioned by 

 the state of the earth's interior, and our 

 knowledge of its constitution is now ad- 

 vancing. So late as the foundation of this 

 society in 1889 the Cartesian doctrine of 

 a fluid earth enclosed in a very rigid shell 

 a score or two of miles in thickness was 

 held by most geologists. "We now know 

 that the globe is solid and on the whole of 

 great rigidity and probably divisible info 

 at least four distinct shells each more rigid 

 than that overlying it, that the irregular- 

 ities in density and structure which are so 

 marked at the surface extend only to a 

 depth of something like a fiftieth of the 

 earth's radius; that open cavities or cracks 

 may exist at depths of 20 miles and very 

 possibly down to the level of isostatic 

 compensation. "We know too that the earth 

 is radioactive but that the radioactivity is 

 superficial, reaching only to a moderate 

 though uncertain level ; we also know, how- 

 ever, that the earth's heat is not wholly 



1 Abstract of the presidential address before the 

 Geological Society of America, December, 1914. 

 The fuU paper is too long for oral delivery and 

 only this abstract was read at the meeting. 



