190 BRIDGMAN. 



so that it was necessary to repeat some of the readings. Four sets of 

 readings were made on the shorter sample, two at 30° and two at 75°, 

 and three sets on the longer sample, one at 30° and two at 75°. The 

 readings on the short sample at 75° were never satisfactory, and those 

 on the long sample at 75° left much to be desired. The readings at 

 30° were fairly satisfactory. 



At 30° the average arithmetical deviation from a smooth line of the 

 readings on the short sample was 5% of the maximum pressure effect. 

 For the long sample the deviation at 30° averaged 5.9% and at 75° 

 4.2%. The results are given by the formulas: 



AV 

 Short sample, At 30° — = - 1(H (5.84 - 2.1 X KHp) p 



y o 



Long sample, At 30° -==- = - 1(H (5.77 - 3.1 X 10^p) p 



I o 



At 75° -p- = - 10- 7 (5.70 - 2.1 X 10^p) p. 



I 



o 



The details of the variation of the coefficients in these formulas 

 probably are not accurate. Because of its greater length the results 

 for the long sample are doubtless to be preferred. Probably the saf- 

 est conclusion to draw from these measurements on gold is merely that 

 at 30° the average compressibility to 12000 is approximately 5.40 X 

 10- 7 , and at 75° it is 5.45 X 10" 7 . 



The compressibility of gold has been measured both by Richards 

 and A. W. J. Richards finds the initial compressibility at 20° of gold 

 of density 19.24 to be 6.3 X 10" 7 , and A. W. J. find the compressi- 

 bility to be constant with pressure, and its value over the range of 

 12000 kg. to be 5.6 X 10- 7 . It is to be noticed that Richards makes 

 gold more compressible than iron, and A. W. J. less. The measure- 

 ments of this paper would seem to leave no room for doubt that it is 

 actually less than iron. It is to be noticed that A. W. J. used a con- 

 stant value for the compressibility of iron, namely 5.9 X 10 -7 . If for 

 this is substituted the new value found above for the average com- 

 pressibility over the range of 12000, namely 5.62 X 10" 7 , A. W. J.'s 

 value becomes 5.3 X 10- 7 , agreeing within one unit in their last signi- 

 ficant figure with the value found above. It is possible that the high 

 value of Richards is due to the fact that his gold was not annealed 

 after the final drawing; the difference is in the same direction as pro- 

 duced by a similar effect in tungsten and molybdenum. 



The low value of the compressibility of gold is somewhat surprising 



