May, 1 9 2 1 . 1 ANISOTROPIC LIQUIDS. 677

recede--from layer to layer--from the central spot so that the radial line gives the intensity of the spectrum.

"~ See Phys. Zeit., 14, lO79, 1913. Tokyo Math.-Phys. Soc., 7, 60, 1913. 4, E . g . , HUPKA: Phys. Zeit., x4, 623, 1913. O. LEHI~ANN: Ann. d. Phys., 2,

676, I9OO, etc. 4~E. BosE: Phys. Zeit., x2, 6o, 1911. A. v. WARTE•BERG: Phys. Zeit., I2, 837,

1911, etc., etc. *~ Dissertation, G6ttingen ; or, Ann. d. Phys., 37, 397, I912. 5o The flat pieces of rubber have this advantage, that they distribute the pressure

evenly over the glass plates; moreover, their thickness could be regulated better than those of the ring.

~t,, Molekulare Bau Flfissiger Kristalle," 1913. Subsequent experiments with crystals mounted on glass showed that this effect is not given by glass plates.

52 Verb. d. Deutsch Phys. Ges., I8/19, 1913.

Double Refraction and Crystalline Structure o~ Silica Glass. LORD RAYLEIGH. (Proc. Royal Society, No. A. 692 . ) - -Ord i - nary glass is not doubly refracting except when under stress. In contradistinction to this the experimenter found that silica glass, pro- duced by the melting of clear, cyrstalline quartz, does have double refraction, though it is only to the extent of one-sixtieth of that of crystalline quartz. When examined by nicol prisms the glass shows a granular structure, possibly due to the pieces of silica melted together to form the piece under examination. Optical silica, built up by a special process, presented, when placed between crossed nicols, an appearance resembling the interference figure of a uniaxial crystal in convergent light. Specimens of this glass were heated to red heat over a period of two hours and were then quenched in water. Con- t rary to expectation, a network of cracks appeared on the surface. Af ter the surface had been repolished examination with the nicols showed no trace of the former pattern. Reheating for ten minutes caused the reappearance of pattern.

G. F. S.

Combined Deve lop ing and Fixing. (Photographic Jour. of America, March, 1921 , p. I24 . ) - -F rench photographers seem to be especially interested in bizarre processes, and among these have in- vestigated the methods by which the developing and fixing agents are combined in one solution. They have also given attention to proc- esses in which fixation precedes developmenf, a curious and interest- ing reversal of the usual method, and one that has been but little considered by the writers on the latent image. Lumi~re Brothers and Seyewetz have been especially active in researches along, this line, and in a recent communication to the French Society of Photography