PRESSURE ON RESISTANCE OF METALS. 575 



and Palmer^ to 2000 kg., and Beckman^ with Lisell's apparatus. 

 For a full bibliography the papers of Lisell and Beckmann may 

 be consulted. 



The plan of this paper is to first give the data for individual sub- 

 stances with a description of the details of preparation and the 

 characteristic features of each substance, and then a discussion 

 of the significance of the results. 



Experimental Methods. 



The apparatus is in all essentials the same as that previously 

 used and described in a number of papers ''. It consists of two 

 parts, an upper and a lower cylinder connected by a stout tube. 

 In the upper cylinder pressure is produced by the descent of a piston 

 driven by a ram. The upper cylinder also contains the coil of 

 manganin wire which gives the pressure bj' its change of resistance. 

 The calibration of the manganin coil and the details of the upper 

 cylinder have already been fully described. During the experiment, 

 the upper cylinder was kept thermostatically at a constant tem- 

 perature of 40°. The lower cylinder contains the metal whose 

 resistance is to be measured, and is placed in a second thermostat 

 independent of that controlling the upper cylinder. The resistance 

 of the lower coil was measured on the same Carey Foster bridge 

 as was the manganin wire; connection to the bridge was by mercury 

 switches in paraffine blocks. The lower cylinder is shown in Figure 

 1. It consists of a cylindrical piece of Chrome Vanadium steel 

 pierced axially with a ^ inch hole, enlarged and threaded to receive 

 the connecting pipe at one end and at the other the plug through 

 which the insulating leads connect with the wire under measure- 

 ment. Lower cylinders of two different lengths were used according 

 as the wire to be measured was insulated, and so could be coiled 

 into a narrow space, or was bare and had to be wound in the spiral 



5 A. deF. Palmer, Amer. Jour. Sci. 4, 1, (1897) and 6, 451 (1898). 



6 B. Beckman, (a) Inavig. Dis. Upsala, (1911). 



(b) Ark, f. Mat., Astr., och Fys. 7, No. 42, (1912). 



(c) Ann. Phvs. 46, 481-.5()2 (1915). 



(d) Ann. Ph'vs. 46, 931-941 (1915). 



(e) Phvs. Zs. 16, 59-62 (1915). 



7 P. W. Bridgman, Pfoc. Amer. Acad. 47, .321-343 (1911), and 49, 627-643 

 (1914). 



