VOLUME XXII NUMBER 2 



THE 



JOURNAL OF GEOLOGY 



FEBRUARY-MARCH igi^ 



PRELIMINARY RESULTS OF MEASUREMENTS OF THE 

 RIGIDITY OF THE EARTH 



A. A. MICHELSON 



Ryerson Physical Laboratory, University of Chicago 



Installation and observations by H. G. Gale assisted 

 by Harold Alden. Calculations by W. L. Hart 

 under the direction of F. R. Moulton 



Measurements of the temperature of the crust of the earth as 

 found in the deepest mines show that it rises on the average about 

 0.02° C. for every meter below the surface; and as the rate of in- 

 crease is even greater at greater depths it follows, as Lord Kelvin 

 pointed out,^ that the temperature in the interior must be high 

 enough to melt the substances composing it, and for a long time it 

 was considered that the vast bulk of the earth must be in a fluid, 

 or at least semi-fluid, condition, a conclusion which was strongly 

 supported by the fact of the ejection of molten lava from volcanoes. 



The theoretical investigations of Lord Kelvin in 1863^ indi- 

 cated, however, that the earth must be considered a very rigid 

 body, opposing an enormous resistance to changes of form such 

 as tend to occur in consequence of the attractions of the sun and 

 moon. It is evident from these investigations that the old idea 

 (which is not entirely extinct) that we are hving on a thin rock 

 crust over an immense mass of molten lava must be abandoned. 



^Philosophical Transactions, 1863. ^ Ibid. 



Vol. XXII, No. 2 97 



