GEOPHYSICAL RESEARCH — BECKER. 223 



Dr. J. R. Benton resigned in August to take a professorship of 

 physics, but desires to continue work on crystals in connection with 

 the general investigation. Mr, C. E. Van Orstrand was then put 

 in immediate charge of the observations and Mr. H. B. Ayres was 

 engaged to assist him. 



Dr. Benton has written a paper on the experiments on catgut 

 which is printed in the American Journal of Science. No other 

 material is as yet whoU}^ ready for publication. 



PLANS. 



The conditions requisite to an experimental determination of a 

 stress-strain relation are (i) a constant temperature and (2) a high 

 degree of accuracy in the measurement of the strains. The last con- 

 dition may be obtained by measuring a large elongation with a fair 

 degree of accuracy, or by measuring a small elongation with a high 

 degree of accuracy, for example by the interference method recently 

 used by Mr, Shakespear. It is probable that the stress-strain rela- 

 tion obtained from experiments on small specimens is dependent 

 upon the cross-section of the material. It is well known that small 

 specimens show a tendency to yield abruptly in the vicinity of the 

 point of the so-called limit of elasticity. It is highly probable that 

 no such point exists, but that the transition from the elastic to the 

 plastic state is continuous, beginning at the instant when the smallest 

 load is applied and continuing up to the point of rupture. In 

 order that the investigations be conclusive, therefore, it is desirable 

 that experiments be made upon both large and small specimens. 

 The conditions at the Washington. Monument are perhaps the 

 best that can be obtained anywhere in the world for conducting the 

 experiments on a large scale. Some preliminary experiments have 

 been made to ascertain the feasibility of measuring the strain in 

 small specimens by means of the interference method in our labora- 

 tory. It is possible that the vibrations in the building may be suf- 

 ficient to prevent observations being made, but apparatus is being 

 designed which it is believed will prove to be satisfactory. Attempts 

 will then be made to determine the stress-strain relation for small 

 specimens of crystals, and wires and ribbons of various metals. If 

 the experiments prove to be satisfactory the same apparatus will be 

 used in connection with an electric oven to determine the variation 

 of Young's modulus with temperature. 



