616 BRIDGMAN. 



indicating the correctness of the data of either BeUati and Ronianese 

 or of Lussana. Lussana's method was not one adapted to give 

 accurate results. He measured the time rate of heating or cooling 

 and took the arrest points as the points of transition. These points 

 differed by 5°, and the mean of the two points was taken as the true 

 temperature of transition. The total effect of pressure over the range 

 of 250 kgm. was little more than the width of the band of indifference 

 of the individual measurements. The insensitiveness of the method 

 is indicated by the fact that he found no variation of slope with pres- 

 sure, whereas the variation ought to haAC been easily perceptible even 

 over this low range. Lussana nevertheless, gives the results to three 

 significant figures. 



On the III-IV curve the conditions are similar to those on the II-III 

 curve. Lussana gives for the slope over the first 250 kgm. 0.0137 

 against 0.0135 computed, and Tammann gives for the range up to 

 the triple point the average slope 0.0220. I find for the average slope 

 over the first 250 kgm. 0.0178, and for the average slope up to the 

 triple point 0.0226, in sul)stantial agreement with Tammann. A 

 thoroughgoing comparison of my results with those of Tammann is 

 not possible, because he has not taken any account of the known 

 curvature of the transition line in computing the values at atmospheric 

 pressiu'e. It is evident, howe^•er, that both his results and mine 

 would difter in the same direction from the only other data at at- 

 mospheric pressure, namely those of Bellati and Romanese, and also 

 from those of Lussana. It seems probable that there may be some 

 considerable experimental error in the data of Bellati and Romanese, 

 and that the curvature of the III-IV cur\e, although large, can ac- 

 count for only part of the discrepancies. 



The coordinates that Tammann finds for the triple point II-III-IV 

 are considerably diflferent from mine. He finds 64.16° and 930 kgm. 

 against my values 63.3° and 860 kgm. For the average slope of the 

 II-IV line between the triple point and 90° Tammann finds 0.01404 

 and I find 0.01416. The agreement is better than usual. 



The pressure effect on the transition I-II has been previously 

 measured only by Lussana. He finds 0.0116 for the average slope 

 over the first 250 kgm. against my value 0.00962. 



The measurements of the difference of compressibility of the differ- 

 ent phases at high pressures did not give any ver}- regular results. 

 This much may be stated, however; I is more compressible than II, 

 of the order O.OeS, and is more compressible than VI of the order O.OeS, 

 and IV is more compressible than II of the order 0.068. This last is an 



