VOLUME XXVII NUMBER 8 



THE 



JOURNAL OF GEOLOGY 



NOVEMBER-DECEMBER igig 



THE RIGIDITY OF THE EARTH 



A. A. MICHELSON and HENRY G. GALE 



In 1 9 14, in the March number of the Astrophysical Journal 

 (39, 105, 1914), an account was published of a preHminary experi- 

 ment to determine the rigidity of the earth. At that time it was 

 announced that the experiment would be repeated, using an inter- 

 ference method. The new arrangements were completed and a 

 new series of observations begun on November 20, 1916, and con- 

 tinued until November 20, 191 7. The reduction of the observa- 

 tions was interrupted by the war in the summer of 191 7 and 

 could not be resumed until April 19 19. 



The same pits and pipes on the grounds of the Yerkes Observa- 

 tory at Williams Bay, Wisconsin, were used as in the preliminary 

 ex-periment. In that experiment pipes 502 feet long and 6 inches 

 in diameter were placed 6 feet underground. One pipe was laid 

 accurately N-S and the other E-W. The pipes ended in pits 

 10 feet deep and 8 feet square, walled with concrete. The pipes 

 were carefully leveled, and half filled with water, so that an air space 

 extended from end to end of each pipe, above the water. The 

 pipes ended in air-tight gauges provided with windows through 

 which the changes in water-level could be determined by measuring 

 with microscopes the distance between pointers just below the 

 surface of the water and their totally reflected images. 



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