Fletcher — The Melting -Points of some of the Rarer Minerals. 469 



as obtained by this method, placed side by side upon the meldometer ribbon 

 and heated together, is evident. 



These wide differences are limited to certain specific cases of minerals, and 

 melting-point standards obtained in a similar manner have agreed in 

 producing an even slope in the foregoing curve of extension, fig. 3, p. 446. 

 It is possible that the cause may be sought for in crystallographic changes 

 (rather than in differences in purity) occurring only under certain conditions 

 of observation, which might lead to varying I'esults by methods so diverse as 

 those used by different observers. 



I beg to record my thanks to Professor Joly for permitting me to continue 

 his work on the meldometer. 



IvEAGH Geological Laboeatoey, 

 Trinity College, Dublin. 



November 2,6th, 1912. 



SOIENT. PEOO. E.D.S., VOL. XIII., NO. XXXI 3 Z 



