ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 503 



used, and they offer the advantages of comparative independence of 

 cover-glass thickness and a brighter image. 



The circular describes many of the details of manipulation necessary 

 for success. 



(4) Photomicrography, 



Colour-screens for Colour-photography.* — An extremely ingenious 

 method of producing colour-screens for colour-photography has re- 

 cently been invented by S. D. M. Hauron and R. de Bercegol, of 

 Joinville-le-Point (Seine), France. 



A sheet of glass, celluloid, or other suitable material is covered with 

 a material that is permeable to water, such as gelatin. Over this is 

 spread a coloured varnish impermeable to water. Small parallel bands 

 or tracks, separated by intervals equal to their width, are drawn by a 

 ruling-machine. The sheet is dipped into a water-colour, which im- 

 pregnates the gelatin exposed by the tracks. This produces a two- 

 colour screen. To produce a third colour, a second protecting varnish 

 is spread ; by the same ruling-machine tracks are hollowed out trans- 

 versely and at intervals of double their width, deep enough to expose 

 the lower layer of gelatin, which the water-colour above used has not 

 penetrated. The sheet is dipped into a water-colour bath of a third 

 colour, producing a three-colour screen. The process is variously 

 modified. A thick coating, superficially coloured, may be employed, 

 and the lines obtained by successive varnish coatings, rulings, and 

 water-colour baths. A coloured celluloid base may be used, coated 

 with gelatin, rulings made deep enough to expose uncoloured celluloid, 

 and the exposed celluloid then coloured by a pigment dissolved in 

 acetone, amyl acetate, or like liquid that bites into and penetrates the 

 celluloid. The third colour is obtained by another gelatin coating 

 and similar steps. The gelatin is then removed from the celluloid 

 base, leaving the three-colour screen. Another method of manufacture 

 is to make celluloid sheets with coloured gelatin, rulings made to ex- 

 pose the celluloid, colouring effected with pigment dissolved in acetone 

 as above, a second colourless gelatin protecting layer coated on, and 

 the third colour obtained in the same way. With this modification, 

 two colours may be superposed at the intersections of the lines, if the 

 rulings are made crossing each other. In a fourth modification, the 

 coloured lines are printed from a plate engraved by a ruling-machine. 

 Two sets of lines may be printed by a greasy colouring material, and 

 crossing each other, the third colour being filled in by floating the sheet 

 in a colour-bath to which the greasy colours are impermeable. The 

 screens may be sensitised directly, or they may be detachably connected 

 to the sensitive plate. The transparent support for the screens may be 

 coloured slightly yellow, so as to moderate the activity of the blue-violet 



light. 



(6) Miscellaneous. 



Microscopical Matters.t — W. J. Wood describes some microscopical 

 matters in a letter to the editor of the " English Mechanic," but the 



* English Mechanic, lxxxvii. (1908) p. 295 (3 figs.). ] 

 f Tom. cit., pp. 110-11 (1 fig.). 



