the Solid Crust of the Earth. 289 



By the Figure of the Earth, </atan qa= —-2, sec q&= —1*2872. 

 Then, putting /=100 miles, /is increased by 0'012115. 



The effect of the fluid would thus be greatly to increase the 

 precession. This increase would, moreover, take place if we 

 allowed any reduction in the pressure in consequence of visco- 

 sity. The friction of the fluid in contact with the solid crust 

 would be a minute quantity not comparable with the effect of the 

 fluid pressure. 



12. Hence, finally, from paragraphs 8, 10, and 11 5 



Calculated Precession for solid earth ... = 51"'36 

 Ditto for solid crust = f^ 51"-36= 61"-41 



Ditto for effect of fluid = ^^ 51"-36 = 198"-41 



6i6b 259"-82 



From both causes, the thinness of the crust and the action of 

 the fluid pressure, the Precession would be increased by a quan- 

 tity so perceptible as to show that, even if at any instant the 

 crust and the fluid revolve alike, this could not continue. It 

 also confirms the previous conclusion in paragraph 9, that the 

 earth's mass can be neither elastic nor fluid to any great extent, 

 but must be highly rigid — as Sir William Thomson has already 

 shown from independent calculations regarding the tides. 



If the advocates for a thin crust say that the pressure at any 

 point in the interior is so enormous, owing to the weight of ma- 

 terials above the point, as to hold the particles firmly together 

 and enable even the fluid portions to sustain unaffected the 

 strain to which they are perpetually being subjected, I say that 

 the interior must have lost its fluid properties, and is actually 

 solid, and that with such a high degree of rigidity as to bear 

 and communicate the strain which comes upon it ; any yielding 

 would be fatal to this effect. Pressure has in that case turned 

 what was liquid at a certain temperature into a solid rigid mass, 

 now at a lower temperature; and the result is, that the interior 

 is solid, not fluid ; which is all I am contending for. 



13. I have shown in this communication that the slowness of 

 the motions of precession and nutation can in no way justify the 

 supposition that the interior of the earth, were it a viscous fluid, 

 would move exactly as the solid crust does ; for in the produc- 

 tion of those motions, slow as they may be, the mass has to un- 

 dergo a strain which no fluid, even if viscous, could sustain. 



It may be thought, perhaps, that nevertheless the latter part 

 of my paper may allow ns to suppose that the interior is fluid, 

 and the crust, though solid, yet not rigid, but possessing a cer- 

 tain degree of suppleness, so that, though the precession would, 



Phil. Mag. S. 4. Vol. 42. No. 280. Oct. 1871. U 



