38 SCIENCE PROGRESS 



more complicated systems. A consideration of a large number 

 of analyses shows that the departures from Penfield and Foote's 

 formula — H 2 oSi4B 2 2 i — are comparatively slight. In a further 

 paper (Cent. f. Min. 1916, 313) the same author criticises 

 Andersen's work on the system anorthite-forsterite-silica with 

 reference to those natural minerals, in the quaternary system 

 lime-magnesia-alumina-silica, which are not represented on the 

 freezing surface. 



Niggli (Zeit. Anorg. Chem. 98, 241, 19 16) extends his 

 investigations of the isothermal equilibrium of systems involving 

 carbon dioxide. S3^stems including the alkali carbonates, 

 lime, titanium dioxide, and silica have been examined and the 

 numerous results obtained are utilised in the construction of 

 pressure temperature diagrams of such complexes as Na 2 0— 

 CaO — C0 2 , Na 2 — Ti0 2 — C0 2 and the analogous potassium 

 systems. 



Le Chatelier (Compt. Rend. 163, 948, 1916) discusses the 

 conditions of formation of cristobalite and criticises Fenner's 

 views regarding the stability of this mineral and tridymite. 

 The latter when heated for a considerable time at 1700 C. 

 showed no trace of conversion to the former. The same 

 author (Bull. Soc. franc. Min. 39, 150, 19 16) has found thin 

 hexagonal plates of tridymite in the devitreflcation products*" 

 of lead glass, thus showing that this habit of tridymite does not 

 necessarily postulate a pneumatolytic origin (cf. Lacroix, ibid. 

 39, 154, 1916). 



Physical Properties of Minerals. — Joly (Phil. Trans. Roy. 

 Soc. A. 217, 51, 191 7) gives the results of a further study of 

 pleochroic haloes. In addition to uranium and thorium 

 haloes, a third type due to radium emanation is described. The 

 structure of the thorium and emanation haloes can be explained 

 by the ionisation effects of the a-rays concerned, but in the 

 uranium haloes, while the outer concentric rings occupy the 

 theoretical positions, the inner ones are slightly displaced. 

 The only feasible explanation of this is that at the period of 

 formation of the haloes (Middle Palseozoic in the specimens 

 examined) the ranges of the a-rays were longer than at present, 

 a hypothesis which might reconcile the radio-active and geo- 

 logical estimates of geological time. 



Balzac (Atti R. Accad. Lincei, 25, I. 811, 1916) has deter- 

 mined the variation of the crystal angles of epidote and clino- 



