IvAMBERT: CONSTITUTION OF THE EARTH 



129 



TABLE 2. 



Stieltjes' Limits of Density Corresponding to Different Distances from 



THE Earth's Center 



like it assume a continuous change of density from surface to 

 center, as of chemically homogeneous matter under pressure. 

 Wiechert^'^ assumes that the central portion or nucleus of the 

 earth is of different material from the outer portion or shell, 

 and that there is an abrupt change in passing from nucleus to 

 shell. The nucleus is supposed to be of metal, chiefly iron, and 

 the shell of rock. In the mathematical form of the hypothesis 

 the density of the iron nucleus is 8.206,^^ its radius 0.78 of the 

 earth's radius; the shell is homogeneous also and of density 3.2. 

 These figures are not entirely arbitrary; they are determined by 

 making the mean density 5.58 and the equilibrium hydrostatic 

 with both the flattening and the value of (C— A)/C conforming to 

 their observed values. The supporters of this hypothesis adduce 

 physical reasons in its favor which are not without weight, but 

 into which I shall not enter. Apart from these it may be used, 

 however, merely for mathematical convenience, as a first rough 



^0 Nachrichten Kbnigl. Gesellsch. Gbttingen, p. 221. 1896-97. 



'' The density of iron is 7.8 under ordinary condition and we may attribute the 

 extra 0.4 of density to pressure or to slight proportions of heavier elements. 



