636 



NATURE 



[January 13, 1921 



there may not necessarily be any immediate ap- 

 plication ol the results to manufacturing^ processes. 

 I'ure research of this nature has already been 

 done, as is instanced by the following list of pub- 

 lished papers : — 



Contrast and Exposuri- in X-ray Photographs 

 throujjh Mitals, by R. K. Sladc (Trans. Faraday Soc, 

 KJI9, vol. .KV., |j, 52). .V discussion of the effects of 

 various qualitiis of X-rays on the pholojjraphic plate, 

 and the possibilities of using jjlates to detect very 

 small flaws in the examination of hirf^e bodies of 

 metal. 



The Fundamental Law for the True Photographic 

 Rendering of Contrast, by A. W. Porter and R. E. 

 Slade {Vm. Mag., 1919,' vol. xxxviii., p. 187). .\ 

 consideration of the conditions which must be ful- 

 filled by photographic materials in order that a true 

 reproduction of the tone-values of an object may be 

 obtained in the final print. 



The Emulsion for a Process Plate, by R. E. Slade 

 and G. I. Higson (I'hot. Jonrn., 1919, vol. lix., 

 p. 260). .'\ description of the type of silver halide 

 emufsion most suitable for a process plate giving 

 great contrast. 



Photomicrography in Photographic Research, by 

 G. I. Higson (Phot. Journ., 1920, vol. Ix., p. 140). k 

 description of a special type of photomicrographic 

 apparatus specially designed for hi^h-power work in 

 the examination of emulsions. 



The Photometric Constant, by G. T. Higson (Phot. 

 Journ., 1920, vol. Ix., p. 161). A mathematical dis- 

 cussion of the relation between the photoinetric 

 density anrf the quantity of silver deposit in .1 photo- 

 graphic plate. 



.\ New Method of Spectrophotometry in the Visible 

 and Ultra-violet and the .-Xbsorptiori of Light bv 

 Silver Bromide, by R. E. Slade and V. C. Toy (Proc. 

 Roy. Soc, 1920, -A, vol. xcvii., p. 181). .\ descrip- 

 tion of a new method free from certain sources of 

 error, by means of which the extinction curve for 

 silver bromide was determined throughout the visible 

 and ultra-violet regions of the spectrum. 



Some Problems in High-power Photomicrography, 

 by R. E. Slade and (i. I. Higson (Trans. T'araday 

 Soc, 1920, vol. xvi., p. loi). .\ contribution to the 

 general discussion on the microscope held bv the 

 Faraday Society. 



.\ Simple Non-intermittent F'xposure Machine, by 

 G. 1. Higson (Phol. Journ., 1920, vol. Ix., p. 235). .\ 

 description of a novel and simple form of exposure 

 machine with which a plate can be exposed to a 

 light of constant intensity for a series of Unown 

 times. 



Photochemical Investigations of the Photographic 

 Plate, by R. E. Slade and G. I. Higson (Proc. Rov. 

 Soc, 1920, -A. vol. xcviii., p. 154). .\n experimental 

 irivestigation of the photochemical behaviour of the 

 silver bromide grain, from which an expression con- 

 necting intensity, time of exposure, and effect on the 

 grains can be deduced. 



The .Absorption of Light by the Goldberg Wedge, 

 by F. C. Toy and J. (.'•. Ghosh (Phil. Mag.. 1920, 

 vol. xl., p. 775). .An investigation of the neutrality 

 of the Goldberg wedge, showing thai this neutrality 

 is confined to the visible portion of the sp«-<trum. 



I?efore the war the manufacturers of cameras 

 made use of wood which had been stained black 

 right through. It was obtained from Germany, 

 and was not procurable in England after the out- 

 break of war. The research association under- 

 took the investigation of such a staining process, 

 with successful results, as may be seen by refer- 

 ence to English Patent No. 17.638/19. It now 

 remains for the manufacturers to develop the pro- 

 cess on a commercial scale. At the same time, a 

 quick process fcjr staining wood brown right 

 through was devised. 



The methods of making sensitive emulsions for 

 coating on plates and papers have been brought 

 to a high standard of excellence by the various 

 English manufacturers. To a large extent, how- 

 ever, the methods used are the result of experi- 

 ence, of trial and error; different manufacturers 

 obtain similar results by widely different methods. 

 .•\n inexhaustible field of work is open for the 

 definite correlation of the physical and chemical 

 properties of the materials used with the methods 

 emploved and the sensitiveness and other char- 

 acteristics of the emulsion obtained. .\ commence- 

 ment is being made on this line of work, the tech- 

 nical heads of the various firms putting their ex- 

 perience and knowledge at the disposal of the re- 

 search association. .Any useful results obtained 

 in the research laboratories will then be tested on 

 a large scale in the works, since it is more than 

 usually diHicult in emulsion-making to pass suc- 

 cessfully from the laboratory to the works scale. 



There is also need for improved methods of 

 laboratory testing of the raw materials of the in- 

 dustry so as to establish greater confidence be- 

 tween buyer and seller, particularly in regard to 

 gelatine, bromides, raw and baryta-coated papers, 

 and packing materials. 



The literature of photography is very scattered, 

 and, doubtless owing partly to the subtle nature 

 of manv photographic phenomena, important de- 

 tails have often been overlooked, with the conse- 

 quence that the results of different workers often 

 apf>ear verv contradictory. One of the objects of 

 the research association is to collect and sum- 

 marise this literature so that it may be placed 

 at the disposal of the members of the association. 

 Progress is being made in this direction, but it is 

 necessarilv slow. 



Obi 



Sir Lazarus Fletcher, F.R.S. 



T)Y the death of Sir Lazarus Fletcher, 



-U mineralogy lo.ses one who for a long period 



was recognised as the leading exponent of that 



branch of science in this country. Born at Salford 



on March 3, 1854, Sir Lazarus died suddenlv from 



heart failure at Grange-over-Sands on January (1 



in the sixty-seventh year of his age. He was 



educated at the Manchester Grammar School, and 



NO. 2672, VOL. 106"! 



tuary. 



afterwards at Balliol College, Oxford, where he 



I held the Brackenbury science scholarship. He 

 obtained first-class honours in mathematical 



, moderations and in the final .schools of mathe- 

 matics and natural science. F'rom 1875-77 he 



' served as demonstrator in physics under Prof. 

 Clifton at the Clarendon Laboratory, and for the 



I next two years he held the Millard lectureship in 

 physics at Trinity College, Oxford. From 1S77-80 



