Hennessy — 0)1 the 3Iolecular Influence of Fluids. 63 



atljacent internal strata would remain undisturbed. When the expe- 

 riment is actually made, the observed and calculated form of surface 

 agree very well. But this arises because the whole fluid possesses 

 internal viscidity whereby each stratum has a grip on that which, it 

 encloses, and it cannot rotate without pulling the other. 



A mathematician, to whom allusion has been already made, is re- 

 ported to have declared that the conclusion I put forward, as to the inte- 

 rior fluid 01 the earth and its containing solid shell rotating as one mass, is 

 "a mechanical impossibility." In making this remark, he had in view 

 the purely ideal substance called a perfect fluid. The experiments I 

 have ali'eady made seem to show that, for a natural fluid, the pheno- 

 mena of its rotation are in harmony with my conclusions, and widely 

 different from those of the ideal substance commonly defined as a fluid 

 in connexion with mathematico-physical theories. In the course of 

 the discussion on the precessional motion of the earth considered as a 

 solid shell enclosing a mass of fluid, it was asserted that the slowness 

 of the precessiona] motion had nothing to do with the relative veloci- 

 ties of the shell and its contained liquid. The experiments I have 

 made show, on the contrary, that the relative velocities are closely 

 dependent upon the absolute velocity of the solid envelope, and when 

 this moves slowly the liquid is carried along with it as if the whole 

 were one mass. 



