ANALYTICAL ABSTRACTS. 20 3 



earth. From a study of these curves Mr. King is led to conclude that in order 

 to satisfy the conditions of tidal effective rigidity there can be no considerable 

 fused couche within the upper .06 of radius. And since for a given initial 

 temperature the temperature gradient decreases as the period of refrigeration 

 lengthens, an excessive period produces too low a gradient at the surface to 

 satisfy observed rates of heat-augmentation. 



To meet both these requirements Mr. King selects a gradient which falls 

 below the diabase line of fusion, and emerges at the earth's surface at a rate 

 not less than the mean rate of 64 ft. to 1° F. This corresponds to an initial 

 excess of 1950" C. and a period of 24X10^ years. 



Corrections which should be made to the assumed rate of refrigeration are 

 considered, and found to modify the result but slightly. 



In comparing this method of determining the age of the earth with that 

 by Kelvin, based on tidal retardations. King contends that, from abundant 

 geological observation plasticity must be admitted for slow deformations, 

 enormously in excess of the small change of figure which the stress of tidal 

 attraction would produce but for elastic resistance. And although rigidity 

 prevents a sudden tidal deformation of five feet, it does not prevent a slow 

 radial deformation of five miles of the surface matter. ' Hence it appears that 

 no time measure can be deduced from the supposed fixing of the present 

 ellipticity at some past date. 



A very significant comparison of the earth's age is made with that of the 

 sun, which, according to Helmholtz and Kelvin, is isXio*^ to 2oXio« years. 

 It is remarked by Newcomb that the period during which the heat received 

 by the earth from the sun has been of a temperature which would permit 

 water to exist in a liquid state upon the earth is probably not more than 

 10,000,000 years. King calls attention to the fact that all we know of the 

 earlier strata indicates a water mechanism for their deposition, and that the 

 evidences that life was continuous in them necessitates a climate continuously 

 suitable for the circulation of waters. All of this period therefore must have 

 fallen within Newcomb's limits. And the earth's age, about 24,000,000 }'ears, 

 accords with the 15,000,000 or 20,000,000 found for the sun. J. P. I. 



The Age of the Earth. By Warren Upham. (American Journal of 

 Science, March, 1893). 

 Mr. Upham reviews the estimates which have been made concerning the 

 age of the earth. These range from 10,000,000 to 14,000,000,000 years. 

 The most reliable means, the writer argues, for estimating the age of the 

 earth is through comparing the present rate of denudation of continental 

 areas with the greatest determined thickness of the strata referable to the 

 successive time divisions. He assumes the rate adopted by Wallace of a 

 continental reduction of one foot in 3000 years. Taking Houghton's estimate 



