222 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



irregularity may be. This paper will be chiefly concerned with a 

 careful examination of the suitability of the proposed mercury stand- 

 ard, and a determination of the constants necessary to its use up to 

 6800 kgm. per sq. cm. At the end will be found a calculation from 

 the constants of the mercury gauge of the variation of the specific 

 resistance of mercury under pressure. This calculation involves a 



1000 



2000 



3000 



4000 



.",< X M I 



0000 



700O 



Figure 1. Deflection of free end of Bourdon gauge plotted against pres- 

 sure. Four complete cycles are represented, the points A, B, C, and D being 

 the successive turning points. The figure shows the increasing importance 

 of hysteresis at higher pressures. 



knowledge of several compressibilities, which had to be independently 

 determined. In order, however, not to group together in one paper 

 unrelated matter, the determination of compressibilities under high 

 pressures is made the subject of another paper, and only the numerical 

 results there found are used here. 



