T II E 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] >V << 



DECEMBER 1920. 



13 1920 



LXXX. O/i £/<£ Closure of Small Cavities in Rocks' exposed 

 to High Pressures. By J. Jolt, F.R.S., F.T.C.D.* 



[Plate XVI.] 



IT is now nearly eight years ago since I commenced expe- 

 riments on the behaviour of rocks under high pressures, 

 hydrostatic in character ; the object being, more especially, 

 to determine the stress under which cavities in these materials 

 will close. Data bearing on this point have many appli- 

 cations in Geological science. These experiments extended 

 over a period of nearly two years, from Dec. 1912 to Sept. 1914. 

 Thev were all carried out at atmospheric temperature. It 

 was intended to 'modify the apparatus so as to permit of the 

 temperature being raised and maintained at moderate heights, 

 but the outbreak of war rendered any development in this 

 direction impossible. It appears desirable now to publish 

 an account of what has been accomplished. The method 

 employed seems to possess advantages on the score of 

 directness, sensitiveness, and simplicity over any work of the 

 kind described before or after these experiments by other 

 observers. 



The rock specimen under examination is, as truly as may be, 

 spherical in form. But the sphere is formed of two hemi- 

 spheres accurately fitted together on a plane surface. A 

 small hemispherical cavity is ground centrally in the flat 



* Communicated by the Author. 

 Phil. Mag. S. 6. Vol. 40. No. 240. Dec. 1920. 2 Y 



