CflAr. XIX.] THE SURFACE OF THE EARTH. 207 



out the outer crust of the earth ; and if that outer 

 crust have not sufficient strength to resist the action 

 of gravitation, it must, if sufficiently pHant, have a 

 tendency to undulate all over ; or, if not sufficiently 

 pliant to undulate, its tendency must then be to 

 shiver to fragments. Let us consider in what manner 

 this tendency to undulate or to fracture can be 

 affected by the action of vis-inerti^e. 



We have seen that the action of vis-inertia3 

 resulting from axial rotation, and that resulting from 

 orbital motion, both act westwards in any given part 

 of the surface of the earth when that part of the surface 

 is turned from the sun, but as soon as that part of the 

 surface reaches the point of sunrise, then the conjoint 

 action of those forces ceases ; the orbital force turns 

 eastwards, and acts m opposition to the force result- 

 ing from axial rotation. Thus, then, the alternate 

 conjunction and opposition of these two separate 

 actions of vis-inertiae would control the undulating 

 action of lateral pressure, and cause those undula- 

 tions to take the form of a series of ocean waves 

 sweeping westwards ; for the action westwards is 

 the strongest, and it receives a check during each 

 rotation of the earth. These, then, appear to be the 

 forces which have determined the pecuharities of 

 conformation, which have been so clearly pointed out 

 by the late Rear- Admiral Fitzroy in the following 

 passage, which I extract from the ' Weather Book.' 

 On page 121 of that work Admiral Fitzroy draws 



