134 CARNEGIE INSTITUTION OF WASHINGTON. 



GRAVITY MEASUREMENTS. 



In view of the Director's responsibilities as Chairman of the Advisory Com- 

 mittee in Seismology, the Laboratory has taken much interest in the problem 

 of a comprehensive study of California earth movements. The particular 

 task which the Laboratory undertook was the design of a new apparatus 

 for the determination of the constant of gravity, in cooperation with the 

 U. S. Coast and Geodetic Survey. 



The studies heretofore made of the distribution of density and isostatic 

 adjustment have depended upon measurements with pendulums of different 

 designs and with somewhat ponderous mounting, so that it requires in general 

 about a week for a competent determination of the gravitation-constant at a 

 particular point, and only such points as are reasonably accessible to an 

 automobile truck, upon which the apparatus must be transported, can be 

 included in the plan. For a competent study of isostatic adjustment in a 

 region where the anomalies in the value of g are unusually large, and where 

 the differences of land elevation are very abrupt, a great many more deter- 

 minations are necessary than have heretofore been possible. To secure a 

 proper number of observations and to include among them comparatively 

 inaccessible mountain regions, it is necessary to design a much less cumber- 

 some instrument, if possible without any loss of precision. During the past 

 year preliminary experiments have been undertaken in this direction. 



Brief reviews of the papers published by the members of the Laboratory 

 staff during the current year will be found on the following pages. 



