176 REPORTS ON INVESTIGATIONS AND PROJECTS. 



an easy means of comparing the ordinates of the successive after-effect curves 

 at fixed intervals of time, and therefore gives a load-strain relation for each 

 instant at which the observations are made. Successive loads have been 

 applied in this way at intervals of 5 kg. up to and including 50 kg., with 

 satisfactory results. The strains are much larger than those measured here- 

 tofore, while the accuracy is the same as that of the best methods. The 

 total number of observations made at the Washington Monument during the 

 year is about 1,350. With the exception of a small correction for the varia- 

 tion of Young's modulus with temperature, the computations have been 

 completed, and the data are ready for publication. Not much attention has 

 been given to the theoretical discussion of the experimental results, and for 

 this reason it is perhaps wise to refrain from stating some apparently obvious 

 but important conclusions that seem to be well established by the experiment. 



A second line of work has been to design apparatus to be used in the 

 Physical Laboratory of the United States Geological Survey in studying the 

 variations of Young's modulus for various metals and crystals at high tem- 

 peratures. The preliminary investigations have been completed. An inter- 

 ferometer for measuring strains has been constructed, and a well-equipped 

 electric furnace will be ready for use in a few weeks. A temporary furnace 

 has also been constructed and used to determine the variations of Young's 

 modulus at temperatures ranging from 25° to 65° C. of the steel tapes which 

 have been used in the experiments at the Washington Monument. This 

 furnace will be used during the year to study the after-effect curves for 

 various loads of certain metals maintained at a constant temperature of about 

 25° or 30° C. _ 



Some preliminary work has been done on the variation of electrical resist- 

 ance of a granite containing moisture. 



Bibliography of Geophysics. — For report on this subject see under Bibliog- 

 raphy, page 45. 



