34 SCIENCE PROGRESS 



recently been developed by Farrington, 1 who, however, was led 

 to his hypothesis from a study of the structural characters of 

 meteorites. Suess 2 has further supported the parallel on account 

 of the remarkable and detailed correspondence between the 

 qualitative chemical composition of the ultra-basic rocks of 

 the earth's crust and that of the stony material in meteorites. 

 He proposes three zones as determining the structure of the 

 earth : Nijc (Ni, Fe), the metallic barysphere ; Sima (Si, Mg), 

 the intermediate zone ; and Sal (Si, Al), the outer crust. 

 Merrill 3 has also investigated and discussed the chemical 

 characters of meteorites, and his results show that the elements 

 which he was unable to detect are chiefly those which are least 

 characteristic of terrestrial ultra-basic rocks, and which are, in 

 fact, never abundant on the earth except in acid or alkaline rocks. 



As we have seen above, the parallel can now be carried 

 further than ever before, for to each type of meteorite there 

 corresponds a terrestrial zone of such dimensions that the 

 density requirements are satisfied as closely as could reasonably 

 be expected. In view of this analogy between meteoritic and 

 terrestrial materials, it appeared to the author that it would be of 

 great interest to investigate in detail the radioactive characters 

 of meteorites. Only a few preliminary results have so far been 

 obtained, but they seem to be particularly significant. Radium 

 estimations have been made of the following composites,* this 

 method of analysis having been rendered necessary because 

 the available quantity of each individual specimen was too 

 small to allow of separate treatment. The specimens were 

 detached from a small collection which belongs to the 

 Geological Museum of the Imperial College of Science and 

 Technology, by permission of the authorities of the College, 

 to whom I wish here to express my thanks. The results may 

 be summarised, together with those for average rock types, in 

 the table opposite. 



In 1906 Prof. Strutt 4 estimated the radium in the Dhurmsala 

 stony meteorite, and found it to contain C56 x io~ 12 grams per 

 gram. In the case of three iron meteorites, however, he was 



1 Jourtt. Geol., vol. ix. p. 623, 1901. 

 3 Loc. cit., p. 544. 



3 Am. Journ. Set., vol. xxvii. p. 469, 1909; vol. xxxv. p. 509, 1913. See also 

 Wahl, Zeit. anorg. Chem. t vol. lxix. p. 52, 1910. 



4 Proc. Roy. Soc., A., vol. lxvi. p. 480, 1906. 



