CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



THE MEASUREMENT OF HIGH HYDROSTATIC 



PRESSURE. 



I. A SIMPLE PRIMARY GAUGE. 



By P. W. Bridgman. 



Presented by W. C. Sabine, December 9, 1908. Received December 16, 1908. 



Introduction. 



The classical work of Amagat on various physical effects of high 

 hydrostatic pressure is practically the only work we have in which the 

 pressure has been accurately measured with a direct reading gauge 

 over any considerable pressure range. Amagat's pressure measure- 

 ments were made with his manometre a pistons libres, which is too 

 well known to need description here. The gauge gives consistent 

 results, and throughout the pressure range the indications are propor- 

 tional to the pressure. In fact, the accuracy of the pressure measure- 

 ments is limited only by the accuracy with which the dimensions of 

 the pistons can be measured. With this primary gauge Amagat 

 measured a number of secondary pressure effects, principally the com- 

 pressibilities of various liquids and gases over a pressure range of 

 about 3000 kgm. per sq. cm. The value of the compressibility found 

 in this way has in turn been used by other experimenters as a means 

 of calibrating whatever secondary gauge they found it convenient to 

 use. It is thus possible to avoid the direct measurement of pressure 

 with a manometre a pistons libres, which is in most cases inconvenient, 

 because of the unavoidable leak and the time necessary to make the 

 readings. The care with which the ground surfaces of piston and 

 cylinder must be kept free from grit, and the expense of the instru- 

 ment, are other objections to its common use. 



With increasing experience in methods of reaching high pressures, 

 and increasing excellence of commercial steels, it has been found pos- 

 sible, however, to exceed the pressure limit set by Amagat. Thus 



