GEOPHYSICAL LABORATORY. 171 



depending on the proportions; and for diopside into AbiAn2, k = 0.2, all in 

 square centimeters per second. 



The value 0.25 (close to the maximum experimental value) is taken as 

 probably representing a fair estimate of diffusivity in magmas, and with this 

 as a basis it is shown that such phenomena as the formation of border phases 

 about large bodies of igneous rock by diffusion can not be considered possible 

 in the time available for such action in a coohng magma. On the other hand, 

 the formation of reaction rims about inclusions may be attributed to diffusion, 

 though for very wide rims a considerable period of time will be required. 



(414) Cords and surface-markings in glassware. F. E. Wright. J. Am. Ceram. Soc, 4, 



655-661 (1921). (Papers on Optical Glass, No. 35.) 



In all glass-melting and glass-forming operations there are a number of fac- 

 tors to consider, and the greater the number of definite facts the glass-maker or 

 glass-worker has at hand regarding his particular type of glass, the better is 

 he able to control the operations and the more uniformly excellent is the 

 quahty of the final product. Two of the disturbing phenomena which mar the 

 appearance of glassware are surface markings and cords. In many instances 

 surface markings are wrongty designated as cords, and the wrong remedy is 

 apphed by the glass-maker, who then tries one thing after another, thereby 

 wasting time and money. Fortunately, methods are available for distin- 

 guishing between surface markings and cords, and also for determining the 

 refringence of a cord relative to the glass surrounding it. The glass article is 

 immersed in a tank of liquid of the same refractive index and viewed through 

 the plate-glass sides of the tank, the line of sight being directed toward a 

 distant source of Ught. Under these conditions surface markings disappear 

 altogether, whereas cords and strise are more clearly seen than before. The 

 relative refringence of a cord compared with that of the adjacent glass can 

 also be determined at the same time. For ordinary crown glasses chloro- 

 benzol is suggested as an immersion hquid. To lower its refractive index, 

 add benzol; to raise it, add carbon bisulphide or halowax oil. 



(415) Preliminary note on monticellite ainoite from Isle Cadieux, Quebec. N. L. Bowen. 



J. Wash. Acad. Sci., 11, 278-281 (1921). 



In this paper monticelUte ainoite from Isle Cadieux, Quebec, is described. 

 The rock shows the two olivines, chrysoUte and monticellite, the latter usually 

 in greater amount. The chrysoUte, together with augite, occurs in early- 

 formed crystals; the monticelUte, as well as melilite and biotite, as groundmass 

 minerals that have attacked and resorbed the chrysoUte and augite. Monti- 

 celUte often forms reaction rims around chrj'solite that are in optical continuity 

 with it. 



MonticelUte ainoite is a newly recognized but not a new rock type, for some 

 of the ainoite of the original locaUty is found to hold monticelUte showing the 

 same relationships. 



A fuUer discussion will appear later in the American Journal of Science. 



(418) Note on the determination of the relative expansions of glasses. F. E.Wright. 

 J. Opt. Soc. Amer., 5, 453-460 (1921). (Papers on Optical Glass, No. 36.) 



In this paper attention is called to the appUcation of the methods of polar- 

 ized Ught to the study of the relative expansion of two glasses. The polarized 

 Ught employed for this purpose is produced either by reflection from a poUshed 

 opaque piece of glass at the polarizing angle or by a polarizing prism. The 

 plate under test is examined through a sensitive tint plate and an analyzer 

 sighted toward the polarizer. From the observed change in interference colors 

 the state of radial compression or of radial tension of the glass sample can be 



