GEOPHYSICAL LABORATORY. 155 



(42) A significant instance of galvanometer instability. Walter P. White. Phys. Rev. (2), 



3,491-492 (1914). 

 A radial-field moving coil galvanometer, very free from ordinary tremors, 

 was much deflected by various shocks occurring within the building, and this 

 effect disappeared whenever the supporting shelf was fastened to the wall with 

 sufficient firmness. Apparently, a slight tipping of the shelf was to blame. 

 At any rate, if there had also been any visible tremors of the galvanometer coil, 

 these would have been supposed to be responsible for the trouble. It follows 

 that in other cases where tremors are present, and are supposed to cause 

 troublesome deflections, the real trouble may be due to some other, more easily 

 removable cause. 



(43) Measurements of the extraordinary refractive index of a uniaxial crystal by observa- 



tions in convergent light on a plate normal to the optic axis. H. E. Merwin. 

 J. Wash. Acad. Sci., 4, 530-534 (1914). 



From the following microscopical measurements on a plate normal to the 

 optic axis, an accurate calculation of the maximum double refraction of a 

 uniaxial mineral can be made: (1) the optical character, (2) the thickness, (3) 

 the index of refraction, co, (4) the angular diameter of one of the light or dark 

 rings observed in convergent polarized light. The method involves the 

 calculation of the refractive index of the extraordinary wave along its path to 

 the ring, and the use of this value in the general equation of the index ellipsoid. 



(44) The ternary system CaO-Al203-Si02. G. A. Rankin; with optical study by Fred. 



Eugene Wright. Am. Jour. Sci. (4), 37, 1-79 (1915). 



The purpose of this investigation was to ascertain the stability relations 

 in the ternary system CaO-Al203-Si02, not only from a purely scientific 

 point of view, but also from the bearing of the facts thus discovered upon a 

 number of geological inquiries and upon the problem of the nature of portland- 

 cement clinker. Many papers on this general topic have, of course, already 

 been published, but the work recorded is in the main fragmentary and of little 

 avail in settling the large general questions involved. The present investiga- 

 tion aims to treat the system rather completely, to ascertain the equilibrium 

 relations in the system. To this end all the possible compounds which are 

 found in dry melts of the three oxides CaO, AI2O3, Si02 have been determined, 

 in especial those which are stable at the liquidus; this involves measurements 

 of the respective melting-points or dissociation temperatures, and the deter- 

 mination of the invariant points, boundary curves (monovariant systems), 

 and fields of stability (divariant systems) of the various compounds. 



This paper contains a summary record of the work performed; it is the 

 first thoroughgoing attempt, so far as known, to determine all the compounds, 

 both binary and ternary, of CaO, AI2O3, Si02, and the mutual relations of these 

 compounds, many of which have, of course, previously been made synthetically 

 by others. The data obtained are made use of in a discussion of the nature 

 and constitution of portland-cement clinker and of the formation of certain 

 natural minerals from the magma. 



Three papers dealing with this sytem have already been published from this 

 Laboratory. The first two dealt with the binary systems,^ while in the third^ 

 provisional locations were assigned to ternary quintuple points and boundary 

 curves and the new relations applied in a discussion of the constitution of 

 portland-cement clinker. In the present paper a more exact location is given 



^The lime-silica series of minerals. A. L. Day, E. S. Shepherd, and F. E. Wright. Am. Jour. 

 Sci. (4), 22, 265 (1906) ; reviewed in Year Book No. 5, p. 181. The binary systems of alumina, 

 with silica, lime, and magnesia. E. S. Shepherd, G. A. Rankin, and F. E.Wright. Am. Jour. 

 Sci. (4), 28, 293 (1909) ; reviewed in Year Book No. 8, p. 104. 



^Preliminary report on the ternary system CaO-Al203-Si02. A study of the constitution of 

 portland-cement clinker. E. S. Shepherd, G. A. Rankin, and F. E. Wright. Jour. Ind. Eng. Chem., 

 3, 1-43 (1911) ; reviewed in Year Book No. 9, p. 102. 



