GEOPHYSICAL RESEARCH — DAY. l8l 



(5) The determination of the feldspars by means of their refractive indices. Fred 

 Eugene Wright. Amer. Journ. Sci. (4), 21, 361-363- May, 1906. 

 Of the many methods which have been suggested for the discrimination of 

 the feldspars, perhaps none have received less actual attention from petrolo- 

 gists than those based on the refractive indices, and this, notwithstandmg the 

 fact that the refractive power of a mineral is one of its fundamental proper- 

 ties and can be approximately determined with comparative ease. The 

 method described in this paper is based upon principles developed by Schroe- 

 der van der Kolk some vears ago, but it has proved so effective m actual 

 practice and so thoroughly serviceable in its present form that it has been 

 thought to deserve separate publication. 



(6) Errors in pyrometry. E. S. Shepherd. A paper before the American Electrochem- 



ical Society, May 3, 1906. Published in the Transactions of the Society. 

 The paper is a brief exposition of the errors common to the pyrometric 

 apparatus now in use in the technical laboratories of the country. 



(7) A modification of the Lasaulx method for observing interference figures under 



the microscope. Fred Eugene Wright. Amer. Jour. Sci. (4), 22, 1^20. July, 1906. 

 A description of a convenient device by which this well-known method can 

 be applied without the usual disturbance of the microscope adjustment and 

 consequent loss of time. 



(8) The lime-silica series of minerals. Arthur L. Day and E. S. Shepherd. Read before 



the American Chemical Society at Ithaca, June 28, 1906. Extract m Jour Amer. 

 Chem. Soc, 28, 1089-1114. September, 1906. Full text, Amer. Jour. Sci. (4), 22, 

 265-302. October, 1906. 

 The feldspar investigation, published a year ago, was a study of a typical 

 isomorphous mineral series without any breaking down of the components, 

 limitations of solubility, or other complicating phenomena. In the interest 

 of a systematic progression, it therefore seemed desirable to undertake an 

 equally careful study of the eutectic relation. A further reason for under- 

 taking this series lav in the fact that the most important single mineral con- 

 tained in it had been made the subject of a special investigation during the 

 previous year. The most important results of the investigation may be 

 brieflv stated as follows : In addition to lime and silica, the initial components 

 of the series, only two compounds of these are capable of a stable, independent 

 existence These are wollastonite, which was found to exist m two different 

 crystal forms, one of which (the common form) is stable below 1,200 ; the 

 other is stable only above that temperature. It was found possible to prepare 

 both these forms in high chemical purity and to transform them from one to 

 the other, thereby establishing all the conditions of their equilibrium The 

 melting-point of the higher form was found to be 1,512°. The second stable 

 compound of these minerals is the orthosilicate of calcium, containing two 

 molecules of lime to one of silica. Three different crystal forms of this mm- 



