THE PHYSICAL FORMATION OP THE EARTH. 



193 



Thoro are many indications of tlio probable fluidity of the 

 globe at one time — the appearance of some geological strata, 

 natural crystalline formations, the estimated present tem- 

 perature of the earth's interior, — those may bo taken as 

 oxamplos. And accepting this, it may be experimentally 

 demonstrated that a liquid mass would assume the oblate 

 spheroidal form taken by the earth when subjected to the 

 forces which acted on the bitter. Li(]uid masses when freed 

 from the action of the earth's force, form themselves into 

 spheres on account of the mutual attraction, existing be- 

 tween the particles of which they consist, as the sphere is 

 the figure which will give the least possible average inter- 

 molecular distance. Oil suspended in a mixture of alcohol 

 and water of its own specific gravity can be used to show 

 this. To complete the imitation of the formation of such a 

 spheroid as the earth, the spherical oil-globulo should be 

 rotated, when it will flatten in a direction perpendicular to 

 the axis of rotation, in obedience to the first law of mot-ion 

 as enunciated by Newton. If a very rapid rotatory motion 

 bo communicated to the globule, portions will be flung off 

 (a,s lj,'ipla,(K! supposed did happen in the case of the sun) 

 and will form smaller globules. 



Various stages of formation by a process similar to that 

 which produced our earth are exhibited in the other planets 

 of our system, and fi'oin tluise it is apparent that the polar 

 flattening varies with the rate of rotation and the greater 

 or less plasticity of the masses (as can be further shown 

 by experiment). 



From the amount of the earth's compression (^y^^ of its 

 equatorial diameter), it has been attempted to estimate its 

 age. Its rate of revolution is decreasing, probably owing 

 to tidal friction. Supposing that this has remained con- 

 stant, then 1,000,000,000 years ago it was revolving on its 



