GEOPHYSICAL RESEARCH — ADAMS, BECKER. 175 



Simultaneously investigations have been made into the structures developed 

 in the harder plutonic rocks of the earth's crust, as, for instance, diabase, 

 essexite, and granite, by differential movements under conditions of heat 

 and pressure, which reproduce those which there is reason to believe obtain 

 in the earth's crust in the zone of flow. This experimental work forms a 

 continuation of that which has already been carried out with the softer 

 rocks, such as limestones, dolomites, etc. 



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, and Year Book No. 

 4, pp. 221-223.) $7,500. 



During the past year the work on elasticity has been conducted along the 

 two lines indicated in the last report. The first has been a continuation of 

 the tension tests on steel tapes suspended in the Washington Monument. 

 Preliminary observations proved the need of accurate temperature measure- 

 ments. This was first accomplished by measuring the electrical resistance 

 of copper wires placed inside the closed tube containing the tape. New tapes 

 were procured later, and were calibrated electrically in the laboratory before 

 being put in place. The measurement of electrical resistance by means of a 

 galvanometer and a standard resistance-box affords a simple and suflSciently 

 accurate method of determining the mean temperature of the tape. Inci- 

 dental to the measurement of temperature, the method also affords a very 

 satisfactory means of investigating the variation of temperature and the 

 variation of electrical resistance with strain, subjects on which existing data 

 are not conclusive. The importance of a thorough investigation of the after- 

 effect curves as a means of elucidating the phenomena of elasticity was 

 emphasized in the last annual report, and the observations made during the 

 year amply justify these conclusions. As was there stated, the complete 

 solution of the problem would consist in determining the after-effect curv^es, 

 and in particular the asymptotes to these curves, for the various loads. 

 Owing to the limited time for which the use of the Washington Monument 

 had been placed at the disposal of Dr. Becker, he decided to spend about six 

 months of the year in making observations for the complete after-effect curve 

 for small loads (5, 10, and 15 kg.) well within the so-called limit of elas- 

 ticity. The remainder of the time has been spent in studying elastic fore- 

 strain in a manner quite different from the usual method. A load was applied 

 and allowed to remain about two hours, observations in the meantime being 

 made at fixed intervals of time during the progress of the strain. The load 

 was then removed, and the specimen allowed to rest three or four days for 

 the larger loads, until it had completely regained its initial dimensions, after 

 which a second load was applied, and the observations again made at the 

 same time-intervals after the application of the load as before. This gives 



