} On the Evidence that the Earth's Interior is Solid. 773 
_Itmay indeed be said with Professor Dana: “ Among geologi- 
al facts none appears to demand for its explanation a rigid globe. 
The demand has come through the supposed requirements of 
physical laws, studied with the aid of the highest mathematics, 
Whose methods and conclusions are sure only when all the modi- 
fying conditions of the problem are thoroughly understood. 
_ “It is now admitted by some of the best of physicists that no 
-“aguments have yet been present2d which prove the earth to be a 
_figid globe, or to have a rigid crust a thousand miles or so thick; 
and it is also admitted by some mathematicians and physicists of 
, including Airy, the astronomer royal, that the hypoth- 
is of a thin crust over a liquid interior is probably the true one. 
“The science of geology is, therefore, free to adopt the conclu- 
sion which seems best to suit known facts.”! 
_ For further discussions of the state of the earth’s interior 
the reader is referred to 
Barnard’s Papers, “ On the Internal Structure of the Earth considered as affecting 
_ the phenomena of Precession and Nutation,” Smithsonian Contributions, No. 
__ 44°; Pp. 33-48; No. 310, 16 pp. 
meys “Earthquakes, Volcanoes and Mountain-building,” 1871, pp. 68-107. 
he Earth’s crust,” 1881. 
Nature, 1870, 11, 264, 265 ; 1871, 1V, 28, 29, 141, 344, 345; Geol. Mag., 
w 0), vu, 421-424; Phil. Mag., 1859 (4), XVII, 327-332; XVIII, 259-262, 
H43545 1860, Xx, 194-196 ; 1862, XXIV, 409-417, 507-508; 1863, XXVI, 
“S495 1866, XXXI, 430-435 ; XXXII, 17-22, 313-315; 1867, XXXII, 10-16; 
18, XL, tom14 ; 1871, XLI, 307-309 ; XLII, 89-103, 280-290, 400. 
j 1871, Iv, 65; 111, 296-299. 
4 r Nature, Iv, 45, 366, 
Penn Monthly, 1876, vit, 364-378, 417-431- 
in. New Phil. Jour., 1827-28, 1v, 273-290. 
À 1828-29, VI, 84-89. 
ie Am. Jour, Sci., 1874 (3), Vil, 535-546. 
es PP- 147-227; 1875, pp. 1-9. 
s, New York, 1881, pp. 307-330. 
cal Sciences,” 
"eol, 1880, p. 812; see also Whitney’s “ Earthquakes, Volcanoes and 
Iiding 1871, P. 74. 
