770 



SUMMARY OF CUREENT RESEARCHES RELATING TO 



of Photographische Chronik. It deals with the preparation and use 

 of screens of diffused metallic surface, whereby a greater degree of 

 luminosity of projected picture is obtained. The higher the reflecting 

 power of the screen the brighter will be the picture, and this considera- 

 tion is of especial importance when the magnification is large, as it is in 

 the case of cinematograph displays. Hence attempts have been made to 

 produce screens with a metallic surface. Silvered glass has been used, 

 but most successfully when the silvering has been applied to the matted 

 instead of the polished face. 



This silvering of the screen was the method employed by Lewis 

 Wright in 1899, when he gave a display before our Society.* Instead 

 of using silvered glass, however, Wright applied silver to a surface 

 minutely ribbed or striated in a vertical direction, and the result was that 

 not only persons sitting in front of the screen, but also those at the 

 sides, could |see. Wright also exhibited his screen before the Quekett 

 Microscopical Club.f 



Lehmann seems to have re-discovered Wright's process, but varies it 

 by substituting aluminium for silver on a specially prepared and per- 

 manently rippled paper. He finds that, by suitable choice of the furrow 

 or indentation on the screen, the distribution of the brightness may be 

 regulated to a certain extent. It is best not to apply the aluminium as 

 " paint," or, more strictly, as emulsion, but to apply a foundation of suit- 

 able viscosity and then to dust over with dry aluminium powder. The 

 picture produced is extraordinarily bright, and reveals details of colour 

 and structure which are quite unattainable on ordinary screens. 



The same number of the Monthly Supplement $ notices an article on 

 the same subject by Baron von Hiibl, contributed to the Wiener Mitteil- 

 ungen. The Baron discusses the angles within which persons in the 

 auditorium would have the best view. Diagrams are given, and fully 

 illustrate the necessary conditions. 



Pig. 121, 



' " Koristka's Paraboloid Condenser.§— This condenser (fig. 121) is 

 modelled on that of Siedentopf — the central part of the inferior surface 

 is rendered opaque by means of a diaphragm, so that the emergent light 

 is peripheral. 



* See this Journal, 1899, pp. 247-8. 



+ Journ. Quekett Micr. Club, ser. 2, vii. (1898-1900) p. 241. 



t Tom. cit. ; p. 47.' § Koristka's Catalogue, xiii. (1908) p. 55, fig. 28. 



