28 ILLINOIS ACADEMY OF SCIENCE 



Truly, the investigation of the mineral resources and in- 

 dustry of the country covers a magnificent field of the highest 

 importance to the nation's life and prosperity. Considering 

 the brief span of years already employed, the knowledge of 

 distribution, character, and utilization of our mineral wealth 

 is surprising. Furthermore, when it is remembered that the 

 most rapid contributions to knowledge and most extensive 

 development in operations have come during the last fifty or 

 even thirty years, the promise for increased efficiency and 

 scientific development and management in the near future is 

 exceedingly bright. 



RIGIDITY AXD VISCOSITY OF THE EARTH. AND 



THE BEHAVIOR OF SUBSTANCES UNDER 



STRESS 



A. A. MICHELSON, UNIVERSITY OF CHICAGO 



The experiments recently conducted at the Yerkes Ob- 

 servatory for the purpose of ascertaining the action of the mass 

 of the earth in yielding to the gravitation forces of the sun 

 and the moon, gave the result that the earth acts like a solid 

 body with an elastic coefficient of the order of that of steel — 

 and with a coefficient of viscosity which is very high — prob- 

 ably also of the same order as that of steel. 



For detailed account of these experiments, see Journal of 

 Geology. Vol. XXII, No. 2, 1914. 



From the known increase of temperature as we go below 

 the surface of the earth, it follows that the temperature of 

 the interior must be very high — high enough to melt almost if 

 not quite all known substances under normal conditions. 



It follows that the enormous gravitational pressure which 

 the mass of the earth experiences is sufficient to prevent this 

 fluid condition — in other words, that pressure increases elastic 

 rigidity as well as viscosity. 



An attempt was made to detect such an effect, using the 

 relatively small pressures obtainable in the laboratory (of the 

 order of 50,000 pounds per square inch) and the results ob- 

 tained clearly confirmed this conclusion. However, certain 

 rather curious and baffling anomalies presented themselves 

 which made the results less conclusive than was anticipated. 



The study of these anomalies has been in progress for 

 several months and an account of the results will probably be 

 published as soon as the information obtained is available. 



