BRIDGMAN. — MERCURY UNDER PRESSURE. 365 



An attempt was made to show directly the presence of warping by- 

 measurements of the change of length of the exterior of the cylinder. 

 Measurements of the extension were made over the middle third and 

 the middle two thirds of the cylinder. Any very large warping might 

 be expected to destroy the proportionality of extension to length, since 

 presumably the warping is confined to the neighborhood of the ends. 

 No such effect could be found, however, within the limits of error which 

 were about 1 per cent. 



The argument for the probable absence of warping may be stated as 

 follows. The change of internal length of the cylinder with which we 

 are concerned was measured between two points at each of which the 

 internal diameter of the cylinder undergoes an abrupt change. If the 

 elastic limit of the steel were exceeded, the resulting set and hetero- 

 geneity would naturally appear first at these places of sudden change 

 in the dimensions. The effect of heterogeneity at these places would 

 be to produce warping, that is, sections originally plane would no longer 

 remain plane. On the other hand, if the material were never strained 

 beyond the elastic limit, the warping would be negligible. Now the 

 cylinder has been shown by direct experiment to show no hysteresis, 

 and therefore probably not to have been strained beyond the elastic 

 limit. The cylinder, therefore, probably also shows no warping. In 

 any event, one would seem justified in accepting the readings of a 

 cylinder showing no hysteresis in preference to one where the hystere- 

 sis might amount to 16 per cent. The effect of warping, whatever it 

 is, can be only slight, since it is itself only a correction on a 5 per cent 

 correction term. 



The new determinations made for this work with the nickel steel 

 cylinder were made on the same specimens as those formerly used, 

 which were from the same piece of steel as the piezometers. Deter- 

 minations were made at two temperatures, 10° and 50°, and up to 10,000 

 kgm./cm.^ There were only a few changes from the experimental pro- 

 cedure of the previous work. Pressure was measured by measuring the 

 change in the electrical resistance of a coil of manganin wire, instead 

 of a capillary of mercury. This is the pressure gauge that was used in 

 the later work of this paper, and it has been described in detail in a 

 previous paper. The fluid transmitting pressure was usually kerosene 

 instead of the former mixture of water and glycerine. At 10° and at 

 pressure above 8000, the kerosene becomes so viscous that the ring on 

 the test rod no longer slides freely. The great irregularity of the 

 points first obtained was traced to this effect. It may be avoided by 

 using gasolene instead of kerosene at the higher pressures. At 50° 

 the kerosene may be used without trouble over the entire pressure; 



