temperature of the interior of the earth. 1 27 



drogen : but to very few in England, except Harrowgate, and 

 two or three others. 



"22. If we judge from the lavas, the fluidity of the incande- 

 scent matter which constitutes the interior of the earth would 

 be very great ; and its density in places distant from the center, 

 as ll of the radius, would be much inferior to the mean densi- 

 ty of the whole globe." (The density will no doubt be in a cer- 

 tain degree the result of superincumbent pressure.) " These two 

 data are not in opposition to the influence which we must allow 

 to the enormous and increasing pressure ascrihable to the central 

 forces. It must however be remembered that liquids are not 

 easily compressed ; that this compressibility must have a limit ; 

 and that excessive heat may counterbalance its effects. More- 

 over, lavas actually have a greater mean specific gravity than 

 that of primitive rocks in general : whence we may conclude, 

 independently of any other consideration, that the density of the 

 central substances depends more on their nature, than on the 

 compression they undergo. They have been arranged originally 

 in the order of their specific gravities. The existence of gold 

 and platinum proves that matters of very great specific gravity 

 maybe found at the center of the earth." 



The obsidians, the pumice, the pearl stones, the volcanic 

 cinders, the trachytes generally, do not possess a greater spe- 

 cific gravity than the average of the primitive rocks. Other 

 lavas, containing a notable proportion of iron, do. We have 

 no proof of the existence of metallic substances near the 

 center of the earth in particular. Gold and silver are found 

 mostly in the primitive and early transition rocks. So are 

 tin, titanium, scheelin, and metallic iron, which could not 

 have been deeply placed in the central mass. 



"2&.^^here is some likelihood in the hypothesis of M. Halley, 

 which ascribes magnetic actions to the existence of an irregular 

 mass chiefly composed of metallic iron, and having a peculiar re- 

 volving motion at the center of the earth. Two kinds of phe- 

 nomena, of which Halley was ignorant, add to this probability. 

 One is, that the rotation of Saturn's ring round that planet, may 

 be called in as furnishing a kind of analogy : the other, that the 

 nature of meteorolites, and the existence of meteoric iron, prove 

 that iron in its metallic state, and alloyed with nickel, may enter 

 abundantly into the composition of planetary masses." 



The mass of Siberian iron, that in the Lyceum at New 

 York, The mass said to exist near the Mandan village, the 



