CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



THE MEASUREMENT OF HYDROSTATIC PRESSURES UP 

 TO 20,000 KILOGRAMS PER SQUARE CENTIMETER. 



By p. W. Bridgman. 



Presented by G. W. Pierce, October 11, 1911. Received October 6, 1911. 



In these Proceedings, Vol. XLV, Numbers 8 and 9, 1909, two methods 

 of measuring hydrostatic pressures were described and applied up to 

 6800 kgm./cm.^ The first method was by means of an absolute gauge 

 of the freely moving piston type; the second method depended ulti- 

 mately on the first, and utilized the change in the electrical resistance 

 of mercury under pressure. The pressure reached with these two 

 forms of gauge was higher than the highest previous accurately meas- 

 ured pressures, which extended to only 3000 or 4000 kgm./cm.^ ; but 

 since the earlier paper, the region of attainable and measurable pres- 

 sures has been still further extended to over 20,000 kgm., so that a re- 

 examination of the gauges there proposed became necessary. Both of 

 the previous methods were found to become inapplicable at pressures 

 much higher than 6800 kgm., the first because of the yielding of the 

 steel of the gauge and the second because of the freezing of the mer- 

 cury. In this paper the modifications of these two methods are de- 

 scribed with which it has been found possible to reach these higher 

 pressures. The freely moving piston gauge has been changed in design 

 so that it has been possible to reach 13,000 kgm., and has been pro- 

 vided with a different reading device. The second method, involving 

 the change in resistance of mercury, has been replaced by another 

 method using the change in resistance of manganin wire. With this 

 an indicated pressure of 20,670 kgm. has been reached. This paper is 

 occupied with a discussion of the calibration, the corrections, and the 

 details of manipulation of these gauges. 



The Absolute Gauge. 



The novel features of the gauge described in the previous paper 

 which made it possible to more than double the pressure range of 



VOL. XLVII. — 21 



