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



IL— On the Age of the World as depending on the Condition 

 OF the Interior. 



By the Eev. 0. Fisher, M.A., F.G.S. 



IN Nature of tlie 7th of March, Lord Kelvin reported the results 

 of a series of experiments, which render it almost certain that 

 Prof. J. Perry's hypothesis of the conductivity of rock increasing 

 with the temperature is unsupported by evidence. He also stated 

 that he had been led by later study to modify his original estimate 

 of the age of the world, and to reduce it to about the same as 

 estimated by Mr. Clarence King, viz. 24 million years. Thus 

 geologists would find themselves restricted to a still shorter period 

 for the evolution of the events of the world's history than they 

 supposed. 



It must, nevertheless, be carefully remembered that the estimates 

 of the world's age above referred to proceed upon the hypothesis 

 that the earth is solid throughout, whereas the more obvious 

 interpretation of geological phenomena appears to point to the 

 opposite conclusion, that the crust is comparatively thin, and floats 

 upon a substratum of molten rock of rather greater density than 

 its own. 



The principal argument for the solidity and rigidity of the earth 

 is derived from the existence of tides in the oceans ; for it is held 

 that, if the interior were liquid, there would be subterranean tides 

 in it, which would carry the crust and the enveloping ocean up and 

 down in concert together, so that the measurable depth of the water 

 to the bottom would always remain unchanged; for, although a tidal 

 deformation of the ocean surface would be present, it would not be 

 able to be noticed. It is plain that this apparent obliteration of 

 the tides would require that the deformation in the substratum 

 with its floating crust and the deformation in the enveloping ocean 

 should occur at any given place simultaneously and equally ; that is 

 to say, there would have to be high tide in the crust where and 

 when there was high tide in the water, and low tide in the crust 

 where and when there was low tide in the water, and in each case 

 with the same range of rise and fall. This requires that the surface 

 of the crust should be deformed to the exact shape that the moon's 

 attraction would produce in a liquid globe, and that the same should 

 be the case also with the surface of the ocean. But, seeing that 

 a tide is formed by the local accumulation of matter by differential 

 horizontal flow, it seems highly improbable that the exact form of 

 the tidal spheroid could be produced in the crust, because the 

 irregularities in the under-surface of it, corresponding to and 

 supporting the continental elevations, would so break up and deflect 

 the tide wave in the substratum on which it floats, that the exact 

 form of the tidal spheroid would not be generally maintained 

 beneath the crust, just as it is known not to be maintained at 

 the surface of the ocean owing to the deflection caused by coast 

 lines, whence arise the irregularities known as the " establishments 

 of ports." Thus the exact form of the tidal spheroid would be 



