GSOPHYSICAI, RESEARCH — ADAMS, BECKER. 197 



columns of these rocks, through which small holes have been bored in cer- 

 tain directions, and which have then been placed within heavy steel collars, to 

 pressures representing depths of from 5 to 50 miles below the surface of the 

 earth. 



This investigation, dealing as it does with the question of the depth beneath 

 the earth's surface at which cavities when opened will be closed again by the 

 flow of the surrounding rock into them, is one which has a direct bearing on 

 the problem of the possible extent in depth of mineral veins, as well as on 

 various problems which present themselves in driving deep tunnels. 



The investigation has already furnished very interesting results, but must 

 be carried farther before these can be definitely stated. 



Becker, George F., U. S. Geological Survey, Washington, District of Colum- 

 bia. Grant No. 226. Experiments on elasticity and plasticity of solids. 

 (For previous reports see Year Book No. 3, p. 80; Year Book No. 4, 

 pp. 221-223, and Year Book No. 5, pp. 175, 176.) $7,5oo. 



Systematic observations on the steel tapes suspended in the Washington 

 Monument, for a determination of the after-effect curves, were continued 

 until the middle of March. In the two months following, a great number of 

 observations were made on elastic fore-strain and on the variation of tem- 

 perature and electric conductivity with strain. A simple method of recording 

 the amplitudes of the longitudinal vibrations of the tape when suddenly 

 loaded was devised and successfully applied. Although the accuracy by this 

 method of mieasurement is not comparable with that of the cathetometer, the 

 data are, nevertheless, of great value in a study of instantaneous strain. The 

 periods of the longitudinal vibrations of the strained tape for various loads 

 were accurately determined from the records of a chronograph. The final 

 reduction and discussion of all of the data obtained at the Washington 

 Monument is now in progress. 



The electric furnace and measuring apparatus mentioned in the last report 

 have been completed and a few observations have been made on the varia- 

 tion of Young's modulus with temperature, due account being taken of the 

 after-effect. It was intended to begin systematic observations with this 

 apparatus when the work at the Washington Monument was completed. 

 There has been some delay on account of the removal of the laboratory equip- 

 ment from the U. S. Geological Survey building to the Geophysical Labora- 

 tory of the Carnegie Institution of Washington. The new conditions, how- 

 ever, are much more favorable for the prosecution of this investigation, and 

 it will probably be possible to obtain a series of observations extending over 

 a long interval of time, on specimens maintained at a nearly constant tem- 

 perature and practically free from vibrations. 



Bibliography of Geophysics.— See under Bibliography, pages 46-54- 



