158 BRIDGMAX. 



pressed tightly into the grooves. The potential terminals were 1.43 

 cm. apart, and the current terminals 2.0 cm. The small resistance of 

 the specimen and the nature of the connections prevented measure- 

 ments of the highest accuracy. Furthermore, it is probable that this 

 specimen was not of high purity, because its temperature coefficient 

 of resistance between 0° and 100° was found to be only 0.00230. In 

 view of the impurity and somewhat low accuracy I made no attempt 

 to find the temperature coefficient of the pressure coefficient, but made 

 the pressure run at a single temperature, 30°. The resistance was 

 found to decrease under pressure, as is normal for most metals. The 

 sign of the pressure coefficient was the most important fact to be 

 iblished by the measurement. The position of uranium as the 

 heaviest of the elements at the end of the periodic table would have 

 given particular interest to a possible positive pressure coefficient of 

 resistance. The average arithmetical deviation of the observed points 

 from a smooth line 'no discards was 1.6* ",- of the maximum pressure 

 effect. It was not possible to detect any deviation from the linear 

 relation between pressure and resistance, and the average pressure 

 coefficient over the range to 12000 kg. was found to be — .0 5 436. 



The specific resistance of uranium seems not to be recorded in the 

 literature. The specific resistance of this sample at 0° was 76.0 X 10 -6 , 

 which is high for a metal, being of the order of magnitude of the re- 

 sistance of liquid mercury or bismuth. 



Caesium. As already mentioned in the introduction, the results on 

 caesium are preliminary, but because of their interest it seems worth 

 while to briefly describe them. The preparation of pure caesium and 

 it> manipulation requires some practise, and I have not yet achieved 

 final success. My original purpose in measuring the resistance of 

 caesium was to search for a more pronounced drop in the temperature 

 coefficient of resistance at high pressures than was found in the case of 

 potassium. It would be expected that there would be such a phenome- 

 non here because of the chemical similarity of caesium and potassium, 

 and because of the much greater compressibility of caesium. This 

 search failed, however, because of the entrance of a new polymorphic 

 form at high pressures. 



The material for the measurements was obtained from the Foote 

 Mineral Co. of Philadelphia. I am also indebted to the kindness of 

 Professor Baxter and Professor G. X. Lewis for other samples, but I 

 was not successful in the manipulation of these. The two samples 

 from the Foote Mineral Co. were provided in glass tubes sealed under 

 oil. One of the samples was apparently somewhat purer than the 



