424 Notices of Memoirs. 



move the whole mass ; and if the earth have a solid crust only, with 

 a fluid interior, the force will have to move only the crust, against 

 the evanescent resistance of the fluid within during so short a space 

 of time as it takes to produce precession. The resulting processional 

 motion will be different in the two cases ; and therefore the actual 

 amount of the precession which the earth's axis has (and which is a 

 matter of observation) is a good test of the solidity or fluidity of the 

 interior. This is Mr. Hopkins's method. 



The force producing nutation is much smaller, even at its maximum, 

 than the processional force. Its effect, however, is precisely the same 

 in this respect — that it depends upon the mass of the solid crust, and 

 in no respect upon the friction of the fluid within it, which has not 

 time to influence the nutation before the nutation is actually produced. 



5. I do not here undertake to go into Mr. Hopkins's numerical 

 calculations ; I simply vindicate his method. I do not here consider 

 what modification the elasticity of the solid materal of the earth may 

 have upon his numerical results. I conceive that it would have no 

 effect, if the disturbing force were constant and there were no 

 nutation. For under the dragging influence (if I may so call it) of 

 the constant processional force, the solid material would be under a 

 steady strain, and would communicate the effect of the force, con- 

 tinuously acting, from particle to particle of the solid part as if it 

 were really rigid ; and the resulting processional motion would be 

 greater or less as the mass of the solid part may be smaller or larger 

 — that is, the solid crust thinner or thicker. But as the disturbing 

 force is not constant, but variable, and there is constantly nutation of 

 the axis as well as precession, the action above described will be 

 somewhat modified ; and the elasticity of the solid material may be 

 expected to have some influence on the result. This influence, how- 

 ever, will be minute, as the part of the disturbing force which is 

 variable and produces nutation is very much smaller, even at its 

 maximum, than the precessional force. The consideration of this 

 matter, however, has no bearing upon the validity or not of Mr. Hop- 

 kins's method, but simply upon the numerical value of his final result, 

 not upon the question of the fluidity or solidity of the earth's mass. 



6. It will appear then, I, think to your readers that the strictures 

 of M. Delaunay upon this method, which the genius of Mr. Hopkins 

 devised, betray an oversight of the real point upon which the success 

 of his method depends, and that this method stands unimpaired. 



iTOTiOES OIF ^vLiEnynoiS/S. 



I. — On the Discovery of a Fossil Snake, Pttuon Euboicus, 

 Roemer, in the Tertiary Calcareous Slates of the Brown-coal 

 formation of Kumi, in the Island of Euboea. By Heee Feed. 

 EoEMEE, of Breslau. 

 [Abdruck a. d. Zeitsclir. d. Deutschen geologischen Gesellscliaft, Jalirg. 1870.] 



FOSSIL snakes are exceedingly rare remains. Prof. Owen has 

 described four species of Palceoplds and two species of 



