GEOPHYSICAL RESEARCH — DAY. 227 



The measurements contained in this investigation do not depend 

 upon the personal judgment of the observer ; that is to say, instead 

 of merely watching a particular mixture until it appeared to melt and 

 then recording the temperature, some physical phenomenon which 

 gave a positive record, like the absorption of heat in melting or the 

 ' release of heat in solidification, was always measured. In this way 

 the personal judgment of a particular observer does not enter into 

 the interpretation of the results. 



A number of technical details and conclusions of interest to spe- 

 cialists were also established, but will not require recounting here. 



A special grant of $1,500 was made by the Institution in February, 

 1905, for the publication of this paper, with suitable illustrations. 

 It was carried through the press and issued during the summer as 

 publication No. 31 of the Carnegie Institution of Washington.* An 

 extract from the paper, under the same title, was printed in English 

 in the American Journal of Science in February, 1905. A second 

 extract in German for the Zeitschrift fur Physikalische Chemie is 

 now in press. 



Pyroxenes. — Upon completion of the experimental work of the feld- 

 spar investigation the laboratory entered upon the preliminary work 

 of a second investigation of the same general character upon certain 

 minerals of the pyroxene group. This group of minerals is perhaps 

 second to the feldspars in importance as a component of the earth's 

 crust, but on account of the wide range of chemical compositions 

 which it includes is a difficult and very comprehensive investigation. 

 The first step in the study was, as before, the preparation of chem- 

 ically pure and well- identified component minerals. The first one 

 to be chosen was the mineral wollastonite, a simple calcium silicate. 



It has been the uniform experience of experimenters heretofore 

 that when chemicals were mixed in the proper proportions for wol- 

 lastonite, and melted, the crystalline product did not prove to be wol- 

 lastonite, but a mineral which does not exist in nature at all. It was 

 therefore determined to investigate the reasons for this and to estab- 

 lish the necessary conditions for the formation of a true wollastonite, 

 if one could be made. This has now been successfully accomplished, 

 and we now know that the deciding factor is the temperature at 

 which crystallization occurs ; that when the mineral forms above this 

 temperature the pseudo-form appears and is stable, and when forma- 



*The Isomorphism and Thermal Properties of the Feldspars. Part I, Ther- 

 mal Study, by Arthur D Day and E. T. Allen. Part II, Optical Study, by J. P. 

 Iddings. (With an introduction by George F. Becker.) Octavo, 95 pages, 25 

 text figures, 26 plates. 



