144 SOME APPLICATIONS OF 
IlL.—-SOME GEOLOGICAL THEORIES. 
The belief that the present spheroidal form of the earth necessar- 
ily betokens a previous liquid, or at least, plastic, condition seems 
among geologists almost as universal as the belief that the earth but 
for the development of rotation must have been a spherical body. 
Whether this latter conclusion has any satisfactory basis apart from 
philosophical speculations it is not my present object to inquire. But 
supposing, for the sake of argument, that the natural form of the earth 
as undisturbed by rotation is spherical, the conclusion that it ever was 
in a liquid or even in a plastic state throughout is, according to the 
preceding results, not established by its present spheroidal form. Yet 
even in such a standard work as Geikie’s Text-book of Geology, after 
reading the discussion on p. 12 and the foot-note attached, I fail to de- 
tect a trace of the idea that the polar flattening might be called forth 
by rotation in a truly solid body. 
Various geological writers, it is true, speak of a solid earth as capa- 
ble of changing its form, but they seem in reality to regard the change 
as due to rupture or to the development of a plastic condition. This 
appears, for instance, to be the view actually held by Mr. Herbert 
Spencer in a short paper * entitled ‘‘The Form of the Earth no proof of 
Original Fluidity.” This paper has been referred to with a somewhat 
inaccurate conception of its value and results by two recent geological 
writers, so it claims some notice at our hands. The first of the two 
writers referred to, Mr. W. B. Taylor,t says: “It is now nearly forty 
years since Herbert Spencer, with a juster physical insight [than Sir 
W. Thomson and Prof. Tait], contended and satisfactorily showed that 
a solid earth (of any shape) would assume the oblate spheroidal form 
due to its rate of rotation, as certainly and promptly as if it were 
liquid.” The other writer, Mr. A. Blytt,f amongst other references to 
the paper says, “I believe that Spencer is the first who expressed the 
opinion that even a solid earth can change its form.” 
Mr. Spencer, after some statements as to the relative strength and 
agility of large and small animals, such as elephants and fleas, formu- 
lates the general result that the strength—called also “resistance to 
fracture ”—of a solid structure varies as the square of its linear dimen- 
sions, while the “agencies antagonistic to cohesive attraction,” 7. e., 
gravitational and “ centrifugal” forces, ete., vary as the cube. Except- 
ing a statement that this is obviously true of simple longitudinal and 
torsional stress, the following is the sole proof of his very general law 
supplied by Mr. Spencer: “The strength of a bar of iron, timber, or 
other material subjected to the transverse strain varies as BD?/L; B 
* Phil. Mag., 1847, [3] vol. xxx, pp. 194-196. ; 
t American Journal of Science, 1885, vol. XXX, pp. 258, 259. 
t Phil. Mag., May, 1889, p. 415. Translated from Nyt Magazin for Naturvidenska- 
berne, 1889, Bd. xxx1. Smithsonian Report, 1889: p. 333. 
