June 19, 1921 abstracts: physics 281 



continuity. The resorption relation between the two minerals is 

 plain and the monticellite is here again a groundmass mineral, while 

 the chrysolite occurs as resorbed early crystals. It seems not im- 

 probable that other related rocks may contain monticellite and they 

 should be examined carefully with this in mind. It should be noted 

 that monticellite is readily altered, apparently even more readily than 

 melilite, and its presence is to be expected only in the freshest material. 



Summary. — In this paper monticellite alnoite from Isle Cadieux, 

 Quebec, is described. The rock shows the two olivines chrysolite and 

 monticellite, the latter usually in greater amount. The chrysolite, 

 together with augite, occurs in early formed crystals, while the monti- 

 cellite, as well as melilite and biotite, occur as groundmass minerals 

 that have attacked and resorbed the chrysolite and augite. Monti- 

 cellite often forms reaction rims around chrysolite that are in optical 

 continuity with it. 



Monticellite alnoite is a newly recognized but not a new rock 

 type, for some of the alnoite of the original type locality is found to 

 hold monticellite showing the same relationships. 



ABSTRACTS 



Authors of scientific papers are requested to see that abstracts preferably prepared 

 and signed by themselves, are forwarded promptly to the editors. The abstracts should 

 conform in length and general style to those appearing in this issue. 



PHYSICS. — Polarized light in the study of ores and metals. Fred. E. Wright. 

 Proc. Amer. Phil. Soc. 58: 401-447. 1919. 



In this paper the attempt has been made to present in connected form the 

 electromagnetic theory of the reflection of light from absorbing media, and 

 especially that part of the theory which treats of the reflection phenomena 

 resulting from vertically incident light-waves under the conditions usually 

 encountered in the use of the reflecting or metallographic microscope. Nor- 

 mally incident white light contains, after reflection by an anisotropic sub- 

 stance, a certain amount of plane-polarized light, and this amount increases 

 with the strength of the birefringence and the biabsorption in the crj^stal 

 plate. The presence of plane-polarized light in natural light can be detected 

 by several different methods, such as are used in determinations of sky 

 polarization. For this purpose Koenigsberger adopted the Savart method 

 with rotating glass compensator. A second and new method is proposed 

 which employs either a single calcite cleavage plate with proper aperture or a 

 small portable Koenig-Martens photometer. This method is more sensitive 

 than the first. Methods of this kind, which are based on differences in in- 

 tensity of the reflected components of vertically incident light, are fifty or 

 more times less sensitive in the detection of anisotropism than methods based 

 on the phenomena produced by plane-polarized transmitted light-waves. 



In case vertically incident, plane-polarized light is used, the difference in 

 amplitude of the reflected components causes a rotation of a plane of polariza- 

 tion, and this can be detected and measured by any one of a number of devices 



