368 PROCEEDINGS OF THE AMERICAN ACADEMY. 



o 



men was found to be 3.1 X lO"^ for 100°, against 1.8 X 10"* for 40 

 as found above. Griineisen does not give the temperature coefficient 

 for the iron with the lower compressibility. 



In view of the agreement of the results found here with those of 

 Griineisen, there can seem to be little doubt but that the results found 

 by Richards ** are affected by some constant error as has been claimed 

 by Griineisen. 20 The fact that the results here were found by as near 

 an approach to a direct method as possible, that is, by the measurement 

 of the linear compressibility, which also was the method used by 

 Richards, and the fact that these results agree with those of Griineisen, 

 which were obtained by more indirect methods from the theory of elas- 

 ticity, would seem to nullify Richards' contention that the results of 

 other observers have been in error because the theory of elasticity gives 

 results 30 per cent out of the way. Richards found for iron 38.5 X 

 10~* against 58.3 X 10~* above. Since his value for the compressibility 

 of mercury depends directly on his value for the compressibility of 

 iron, the effect of the correction will be to change very appreciably 

 the value for the mercury, as will be mentioned later. The source of 

 error in Richards' work is not entirely clear. He used an electrical 

 method, in which contact was made with a drop of mercury resting on 

 the top of the rod of iron to be measured. Change of shape of this 

 drop of mercury under pressure seems the most likely source of error. 



The Data for the Compressibility of Mercury and 

 Calculation of Results. 



Determinations were carried out at two temperatures, 0° and 22°. 

 The range is sufficient to give the variation of compressibility with 

 temperature. To get the second temperature derivative of compres- 

 sibility, observations at several other temperatures would have been 

 necessary, as well as a higher degree of accuracy than was possible to 

 attain in this work. The final values given are the mean of a large 

 number of determinations. At 0°, five different piezometers were 

 used, and over 90 determinations made over the pressure range from 

 to 7000 kgm. At 22°, two piezometers were used, and 38 points 

 determined between and 11,000. The points at 0° were ob- 

 tained first and show considerable irregularities. As familiarity 

 was gained with the method, and the several sources of error men- 

 tioned above became recognized, it was found possible to obtain more 



^' Richards, loc. cit. 



20 Griineisen, Ann. Phys.. 25, 849 (1908). 



