TRANSLATOR'S INTRODUCTION xlix 



as great as its present amount, which is 7 |^- of gravity. At 

 present the radius of the equatorial sea-level exceeds the 

 polar semi-diameter by 21 \ kilometres, which is, as nearly 

 as the most careful calculations in the theory of the earth's 

 figure can tell us, just what the excess of equatorial radius 

 of the surface of the sea all round would be if the whole 

 material of the earth were at present liquid and in equilib- 

 rium under the influence of gravity and centrifugal force 

 with the present rotational speed, and \ of what it would 

 be if the rotational speed were twice as great. Hence, if 

 the rotational speed had been twice as great as its present 

 amount when consolidation from approximately the figure 

 of fluid equilibrium took place, and if the solid earth, 

 remaining absolutely rigid, had been gradually slowed down 

 in the course of millions of years to its present speed of 

 rotation, the water would have settled into two circular 

 oceans round the two poles : and the equator, dry all round, 

 would be 64-5 kilometres above the level of the polar sea 

 bottoms. This is on the supposition of absolute rigidity of 

 the earth after primitive consolidation. There would, in 

 reality, have been some degree of yielding to the gravita- 

 tional tendency to level the great gentle slope up from each 

 pole to equator. But if the earth, at the time of primitive 

 consolidation, had been rotating twice as fast as at present, 

 or even 20 per cent, faster than at present, traces of its 

 present figure must have been left in a great preponderance 

 of land, and probably no sea at all, in the equatorial regions. 

 Taking into account all uncertainties, whether in respect to 

 Adams' estimate of the rate of frictional retardation of the 

 earth's rotatory speed, or to the conditions as to rigidity of r 

 the earth once consolidated, we may safely conclude that 

 the earth was certainly not solid 5,000 million years ago, 

 and was probably not solid 1,000 million years ago.' The 

 Age of the Earth, 1897, p. 7 ; cf. Nat. Phil., 830 (1883). 



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