OF ARTS AND SCIENCES. 101 



then Ag, Au, and Cu should melt at 985°, 1,093°, and 1,097°, 

 respectively. Conversely, if Ag, An, and Cu have the Violle 

 melting points 954°, 1,045°, and 1,054°, respectively, then zinc 

 should boil at say 895°, or at least 30° below its apparently well 

 established boiling point. 



These difficulties can only be cleared away by minute inquiry 

 into all the details of experiment involved : for it will be seen that 

 the- relative positions of these (and other) melting points are well 

 preserved, and the work already involves variations of method. 

 The discrepancy increases when higher temperatures are approached 

 (palladium, nickel, platinum, etc.), and it gradually vanishes on 

 reaching lower temperatures. In the former case, however, the 

 limits of the air thermometer are overstepped, and all data are 

 somewhat hypothetical. 



