114 THE METEORITES. — THEIR ORIGIN AND CHARAC'IER. 



being as old as the days of Diogenes Laertiiis, and in recent times has been 

 advocated by Hackley,* Wilcocks,t Williams, $ Sorby, and others. 



If, in the process of condensation of the sun from a gaseous to a liquid 

 state, the metallic portion liquefied before the silicates, would it not in some 

 measure account for the metalhc meteorites being so common in the past and 

 rare at the present time, and for the peridotic ones being the connnon type 

 now ? On account of their specific gravity, meteorites, as a rule, could not 

 be derived from the moon ; unless it should be held that its interior is now 

 much hotter than the earth's interior, and its density made less through 

 that means. This is an improbable supposition on account of its small size, 

 compared with that of the earth, which would lead to its more rapid cooling. 

 Since the specific gravity of the moon, as a whole, is about that of the more 

 common meteorites, and if the law of the increase of density from the sur- 

 face to the centre is the same as that observed upon the earth, it follows 

 that the moon's surface formations must have far less density as a whole than 

 those belonging to the earth. The law of eruption as observed upon the 

 earth is, that the lighter eruptive material as a Avhole is most abundant, 

 while the rocks approaching the mean density of the earth are compara- 

 tively rare, so much so that their presence is generally denied. This law 

 ought also to hold good on the moon, and eruptive material from it, forming 

 meteorites, ought to have less specific gravity as a whole than our granites. 

 The astronomical reasons have usually been regarded as sufficient to show 

 that meteorites could not come from the moon, and that theory is not now 

 especially urged by any one. 



Such a view as advocated by Messrs. Ball and Rodvvell,§ that meteorites 

 were thrown from the earth in past times, is negatived by their general 

 composition, which, as a rule, is different from the exterior portions of the 

 earth. If they were originally terrestrial, these meteorites ought to more 

 commonly possess the characters of basalts, andesites, trachytes, etc. 



Whether the view that meteorites came from the sun demands too great 

 a loss to his mass, since accurate records have been kept, is a problem for 

 the physical astronomer. 



Since it is possible that careful examinations of meteorites by chemical 

 and spectral methods will throw light on the constitution of the celestial 



* Proc. Am. Assoc. Adv. Sci., 1860, xiv. 4-6. 



t I'roc. Ain. Phil. Soc, 186]., ix. 38-l~3S7. 



t Tho Yiw\ of tlic Sun, London, 1870, pp. 131-113. 



§ Sci;niccfor All, iv. 32; Nature, 1879, xix. 193-493. 



