February 24, 192 1] 



NATURE 



841 



We learn from the British Journal of Photography 

 for February 1 1 that at the meeting of the Royal 

 Photographic Society held on February g, Mr. Thome 

 Baker and Dr. L. A. Levy introduced " a new X-ray 

 plate reducing exposure to one-tvventy-iifth," and 

 indicated its special application to radio-metallurgy. 

 The plate is distinguished as the Imperial " Impex." 

 Its extraordinary sensitiveness is obtained by incor- 

 porating the intensifying screen with the plate. The 

 screen consists of a layer of calcium tungstate in 

 soluble gelatine, and is coated on top of the emulsion 

 which is hardened, so that after the exposure the 

 screen can be dissolved off by water at ioo° F. and 

 development then carried out as usual. The screen 

 being in optical contact with the emulsion, an 

 " infinitely smaller " quantity of calcium tungstate is 

 necessary to give the required intensification. The 

 new plate takes a little longer to develop than usual 

 {say 25 per cent.). The size of the particles of the 

 calcium tungstate is some two or three times that of 

 the particles of silver salt in the emulsion. 



The hope has often been expressed that means 

 might be found for desensitising a photographic plate 

 after its exposure, so that its development might be 

 done without the extreme precautions that are neces- 

 sary as to the light employed. This applies with 

 the greatest force to highly sensitive panchromatic 

 plates, which stand so very feeble a light that most 

 persons prefer none at all, trusting to the time of 

 treatment that is supposed to he suitable to the tem- 

 perature of the developer. It has been found that 

 certain substances possess the desired effect to a 

 greater or less degree, but for one reason or another 

 they have not proved acceptable. But "desensitol," 

 which has just been put upon the market by Messrs. 

 Ilford, Ltd., is simple to use and very effective. It 

 is a solution of a red dye, and it is only necessary to 

 dilute it with 50 parts of water and immerse the 

 exposed plate in it, then after one minute the light 

 may be increased to from 200 to 800 times the bright- 

 ness that would previously have been safe, and the 

 plate transferred to the developer and watched in 

 comfort. From a scientific point of view there are 

 many interesting points about such desensitising 

 action, and we hope that we shall soon see the results 

 of investigations into the changes, if any, produced 

 by the desensitiser in the form of the characteristic 

 curve and the proportional colour sensitiveness of 

 plates of various kinds. 



There can be very few officers who served in 

 France who are not familiar with the co-ordinate 

 reference card which was issued by the War Office to 

 facilitate map descriptions and map measurements 

 after the introduction of the application of a cartesian 

 grid to all Service maps up to scales of i : 40,000. The 

 same idea is embodied in the "Romer graph 

 plotter" (A. G. Thornton, Ltd., Paragon Works, 

 49 King Street West, Manchester). A rectangular 

 piece of cardboard (or celluloid), S'xe", is graduated 

 along its edges with the zero graduations at the top 

 right-hand and the bottom left-hand corners. By this 

 means, given two rectangular axes, a point of given 

 co-ordinates can be plotted and the co-ordinates of a | 

 NO. 2678, VOL. 106] 



given point read off without the use of squared paper 

 and as accurately as would be possible if squared 

 paper were employed. The advantages are obvious. 

 Accurate graphs can be drawn in ordinary note-books 

 or on ordinary paper; the attention of the student is 

 concentrated on the graph rather than on the axes; 

 and, more important still, the expense involved in the 

 purchase of squared paper, by no means a small item, 

 is avoided. Teachers of mathematics and science 

 will probably not regret giving this instrument a 

 trial. 



A KiNEMATOGRAPH projector of a new type was 

 demonstrated by Mr. R. J. Trump at the Imperial 

 College, South Kensington, on February 10. The 

 invention of Mrs. Kingsley-Higginson, it employs, in 

 place of the shutter and intermittent film-feeding^ gear 

 of the ordinary machine, a continuously rotating ring 

 of mirrors to stabilise the image and effect the change 

 of picture while the film is run uniformly through the 

 machine. The beam of light is thus always passing 

 unobstructed to the screen, and the alternations of 

 light and darkness produced by the shutter, which 

 constitute the flicker of the ordinary projector, are 

 avoided. The new apparatus can be run quite slowly 

 if required, and in any case there is no necessity to 

 speed it up in the way that is at present usual. The 

 change of picture takes place zone by zone across the 

 screen, which always shows a full image, derived 

 from parts of two successive pictures on the film. 

 The facets on the ring of mirrors are so arranged and 

 set at such an angle that the two lights from the two 

 partial film-pictures which are present at any instant 

 in the gate are separated and transposed into their 

 correct positions on the screen, and join up to form 

 a complete image. There is no dark period and no 

 overlapping or dissolving of the successive pictures 

 into each other, as the first picture disappears at pre- 

 cisely the same rate that the second takes its place. 

 A good and sharply defined image is obtained. The 

 advantages of a uniform feed for the film are con- 

 siderable, in that the wear and tear upon it are much 

 reduced and the risk of breakage is negligible. The 

 application of the same principles to kinemaphoto^ 

 graphy is under consideration, and there is every 

 expectation that useful results will be obtained. 



Messrs. Sotheby, Wilkinson and Hodge will sell 

 by auction at their galleries at 34 and 35 New Bond 

 Street, W.i, on Thursday and Friday, March 3 and 4, 

 a large number (509 lots) of valuable works dealing 

 with natural history and travel, the property of the 

 late Dr. F. du Cane Godman. Many rare books are 

 included, also several long runs of scientific journals 

 and transactions of learned societies. The catalogue 

 should be of great interest to many readers of Nature. 



Sir William Tilden has written for publication by 

 Messrs. George Routledge and Sons, Ltd., a book on 

 "Famous Chemists: The Men and their Work," in 

 which the lives of twenty-one leading chemists, from 

 Robert Boyle to Sir William Ramsay, will be dealt 

 with in a non-technical manner. The sketches, 

 while chiefly biographical in character, will give 

 attention to the social and political conditions of the 



