42 SCIENCE PROGRESS 



which has appeared for some time is one by G. T. Prior (Min. 

 Mag. 18, pp. 26-44, J 9i6) on the classification of meteorites. 

 The chief classification in vogue at the present time is the 

 Rose-Tschermak-Brezina scheme, but this is somewhat arti- 

 ficial, and, particularly in the case of the chondrites, very 

 complicated. Farrington has proposed one which is based 

 on the American Quantitative Classification of igneous rocks, 

 but this naturally is open to the same criticisms as the latter. 

 Berwerth's scheme, based on the metallographic relations of 

 the system iron-nickel, was devised at a time when this system 

 was very imperfectly known, and no use has so far been made 

 of recent work on the equilibrium of this system. In any 

 case such a scheme could only be applied to the iron meteorites. 

 Prior starts from the principle that the source of all meteorites 

 was a nickel-iron poor in nickel and containing other metals 

 in a free state. The first accession of oxygen results in the 

 oxidation of the elements of lower atomic weight, and these 

 unite to form such minerals as enstatite, giving rise to such 

 rare types of meteorites as the Daniel's Kuil meteorite (ibid. 

 pp. 1-25, 1 9 16) in which the iron is all present in the metallic 

 state. The further addition of oxygen results in partial 

 oxidation of the iron and consequent enrichment of the 

 metallic portion in nickel. As the nickel-iron becomes pro- 

 gressively richer in nickel, the silicates becomes richer in iron. 

 Meteorites, therefore, are divided in three classes, chondrites, 

 achondrites, and irons, and each class is subdivided into five 

 groups according to the amount of nickel in the nickel-iron. 



Sir W. Crookes (Phil. Trans. Roy. Soc. A. 217, pp. 411-30, 

 191 7) has carried out spectrum analyses of many aerolites, 

 and concludes that the stony meteorites must have had a 

 common origin, probably being fragments of some cooled 

 planet, as the relative proportions of the four chief metals, 

 iron, chromium, nickel, and magnesium, are more or less 

 uniform. The radium content of a number of meteorites has 

 been determined by T. T. Quirke and L. Finkelstein (Amer. 

 Journ. Sci. (4) 44, pp. 237-42, 191 7), and it is found that in 

 stony meteorites the amount is about one-fifth the quantity 

 present in an average granite, while the iron-meteorites contain 

 practically no radium. 



G. P. Merrill (Amer. Journ. Sci. (4) 42, pp. 322-4, 191 7) 

 notes the occurrence of calcium phosphate in many stony 



