PRESSURE COEFFICIENT OF RESISTANCE. 161 



It was possible to make fairly satisfactory measurements of the re- 

 sistance of the new modification at 0° from the transition pressure out 

 to 12000 kg. On the first application of pressure the results were 

 irregular. This is due to the cracking of the glass capillary under 

 pressure and the consequent change in the geometrical configuration 

 of the caesium due to its extreme softness, but after the seasoning 

 produced by the initial application of pressure the results were regular 

 and would repeat. (The results obtained with the first sample were 

 irregular for the same reason, but no results were found with the first 

 sample that were inconsistent with those given by the second.) The 

 experimental results are reproduced in Figure 3 plotting the measured 

 resistances in terms of the resistance at 3000 kg. as unity. The curve 

 shown was obtained with increasing and decreasing pressure; the 

 points alternately are those with increasing or decreasing pressure. 

 The curve is the same in character as that obtained for the five other 

 abnormal metals in that the curvature is upward, or the resistance 

 increases at a continually increasing rate at the higher pressures. 

 This is most important as suggesting what the mechanism of conduc- 

 tion may be, and is just what would be expected on the basis of theoret- 

 ical considerations which I have already described. The magnitude 

 of the pressure coefficient is high; between 11000 and 12000 kg., the 

 average pressure coefficient of resistance is 0.000493, which is about 

 the same as that of strontium, which has the highest coefficient of the 

 abnormal metals hitherto measured. 



At the transition point there is a discontinuity in resistance in the 

 normal direction, that is, the high pressure phase, or the phase with 

 the smaller volume, has the smaller resistance. I know of no exception 

 to this rule. At 0° the resistance of the high pressure modification at 

 the equilibrium pressure is 0.407 that of the low pressure form. 



I am indebted to my assistant Mr. I. M. Kerney, for help in making 

 many of the readings. 



The Jefferson Physical Laboratory, 

 Harvard University, Cambridge, Mass. 



1 P. W. Bridgman, Proc. Amer. Acad. 52, 573-646, 1917; 56, 61-153, 1921. 



2 G. Reichardt, Ann. Phys. 6, 832, 1901. 



3 L. Holborn, Ann. Phys. 59, 145-169, 1919. 



4 P. W. Bridgman, Proc. Amer. Acad. 57, 41-66, 1922. 



5 P. W. Bridgman, Proc. Amer. Acad, 57, 77-126, 1922. 



6 G. Niccolai, Phys. ZS. 9, 367, 1908. 



