694 CURRENT TOPICS. [J. F. I.

Method of Developing Highly Sensitive and Panchromatic Plates by Ordinary Light. (Photographic Jour. of America, Feb- ruary, 1921 , p. 84.)--Dr. Lfippo-Cramer describes in the Swiss journal, Die Photographie, the following method by which plates that are usually developed in special safe-light may be developed without danger of fog in ordinary light. He found, in the course of studies on sensitizing plates, that the safranin dyes possess the property of diminishing sensibility of silver bromide in a remark- able degree. If to one of the ordinary developers a very dilute solution of phenosafranin (I to 20o0) is added in the proportion of IO c.c. of the color solution to IOO c.c. of the developer, and the plate allowed to remain for about a minute in the mixture, the develop- ment may be then continued in bright yellow light. The plate can be lifted out of the liquid in order to examine the condition of the image, inasmuch as the action of the color is not merely that of a protecting screen, but a deep chemical or physical change in the silver bromide. Lfippo-Cramer states that it is possible to con- duct the development in such a way that a special darkroom illumination is not needed. The plate is immersed in total dark- ness in the color solution for about a minute, and then placed in the developer. Just before this transfer, a stearin candle, placed at a distance of six feet from the plate, is lighted. In this con- venient illumination the development of even very sensitive pan- chromatic plates may be carried out without any danger of fog. Even the liability to chemical fog on the part of the plates sensi- tized with isocyanin is avoided by the method.

Electric Power Production. (U. S. Geological Survey Press Bulletin, No. 469, April, I 92 I . ) - -The total production of electric power by public-utility companies in 1919 was 39 billion kilowatt- hours, according to the Survey. Of this power 62 per cent. was pro- duced by fuels--35 million tons of coal, I I million barrels of oil, and 21. 7 billion cubic feet of gas--the remainder by water power.

The Photo-Electric Theory of Vision. J . H . J . POOLE. (Phil. Mag., March, I92I . ) - - In an address to the British Association in 1919 Sir Oliver Lodge made the suggestion that the sensation of vision might be due to effect of photo-electrons emitted by some substance of the eye under the stimulus of the incident light. It is known that metals emit negative electrons when illuminated under suitable conditions. A careful examination of the black pigment and of the visual purple of the eye was made, but no evidence was secured that they emit electrons. There is therefore no experimental evidence for this attractive and picturesque theory.

G.F.S.