Rev. 0. Fisher— The Age of the World. 245 



niaintained in neither crust nor water surface, and tides would 

 accordingly be observed. If this be a correct explanation, it 

 would seem likely that, where there is an exceptionally large 

 unbroken area of ocean, and consequently a comparatively smooth 

 extent of under-surface to the crust, in such a region the proper 

 form of the tidal surface might be more nearly preserved both for 

 the subjacent liquid rock and for the water, and the measurable tide 

 would consequently be small. Now such is the case in the central 

 parts of the Pacific, scarcely any proper tide being observable at 

 the Sandwich Islands. 



No argument for rigidity can be drawn from a fortnightly tide, 

 because observations hitherto made have not demonstrated that one 

 exists. 



If the above apology for believing in the possibility of a liquid 

 interior can be admitted, it will follow that, the bottom of the 

 crust being constantly laved by molten rock, we should have a 

 mode of communication of heat from beneath which would con- 

 tinually delay the cooling and thickening of the crust, and have 

 an effect upon the temperature gradient at the surface similar to 

 that which would have resulted from Professor Perry's hypothesis, 

 supposing it to have been true. 



If we accept Professor Darwin's theory of the genesis of the 

 moon, there are cogent reasons for believing that interior liquidity 

 is more than probable. 



It seems to be admitted on all hands that the earth was once 

 a molten spheroid, rotating at a speed much exceeding the 

 present of once in twenty-four houx-s. The theory is, that at some 

 early period the moon was thrown off from the earth, and that since 

 that time its distance has gradually increased to the present 

 239,000 miles. This increase in the moon's distance, implying 

 a large amount of work done in opposition to the earth's attraction, 

 has been obtained at the expense of the energy of the earth's 

 rotation, through the medium of tides produced in the earth and in 

 the ocean, but chiefly in the earth itself. The leverage by which 

 the moon has acted on the tidally deformed earth has necessarily 

 been greater at the circumferential than at the central parts. Con- 

 sequently the retardation of rotation has proceeded from without 

 inwards, so that the inward parts have always rotated somewhat 

 more rapidly than the outward, and a consequent friction and 

 generation of heat has been set up within, which has, been much 

 more considerable in the central than in the outer parts. The 

 amount of heat so generated would have been, to use Professor 

 Darwin's own expression, "prodigious," and, upon his estimates, 

 " the whole heat generated from first to last gives a supply of 

 heat at the present rate of loss for 3560 million years." Witk 

 this enormous amount of heat being perpetually communicated to 

 the inner parts (and there does not appear to be any reason why the 

 supply should have hitherto entirely ceased) how could the globe 

 have become wholly solid at the melting temperature for the 

 pressure at every depth ? It seems that, having been once liquid, 



