. Experimental morphology. Protoplasm; Growth. 156 LIGHT AND PROTOPLASM [Ch. VII Extreme ultra-violet \ = fi; 1010 x lO^^ vibrations per second. To obtain monochromatic light from the spectrum, Keinkk's ('84) spec- trophor will be found useful (Fig. 41). In this instrument a beam of sun- light cast by a heliostat through a sUt at H is converged by means of an interpolated lens, O, upon a prism, P, set at the angle of minimum deviar tion. Passing through this prism the rays are dispersed and a spectrum is formed upon a diaphragm D, Dy composed of halves boanding a second slit whose positi
. Experimental morphology. Protoplasm; Growth. 156 LIGHT AND PROTOPLASM [Ch. VII Extreme ultra-violet \ = fi; 1010 x lO^^ vibrations per second. To obtain monochromatic light from the spectrum, Keinkk's ('84) spec- trophor will be found useful (Fig. 41). In this instrument a beam of sun- light cast by a heliostat through a sUt at H is converged by means of an interpolated lens, O, upon a prism, P, set at the angle of minimum deviar tion. Passing through this prism the rays are dispersed and a spectrum is formed upon a diaphragm D, Dy composed of halves boanding a second slit whose position and width may be varied at will so as to include any desired part of the spectrum. A large lens C known as the collector brings the rays which have passed through the second slit to a focus at E. Just in. Fig. 41.— Diagram showing the construction of Reinke's spectrophor and the path of the rays in it. H, slit next to heliostat; 0, pro- jecting lens; P, prism; S, Si, scale marted with wave lengths; D, Di, diaphragm, including a variable slit; c, ci, collecting lens; B, posi- tion of object subjected to the rays. The spectrum ranges from A = ;ia to A = 40 fi. (From Eeinke, '84.) front of the diaphragm is placed a scale 5, S^ of wave lengths fitted to the spectrum obtained. Such a scale may be constructed with reference to the position of Frauenhofek's lines by interpolation from Fig. 40.* To in- clude rays whose wave lengths differ by exactly /ix the slit must be wider when at the blue end than when at the red end of the spectrum (Fig. 40). to form a hollow, triangular (60°) prism. The plates are fixed to each other and to the glass base by a pasty cement made by mixing plaster of paris and liquid glue. This cement soon hardens, and is not attacked hy the carbon disulphide. The hollow prism is now filled with fluid, and a triangular glass plate is cemented on as a cover. * If artificial light is used, two points on the scale can be obtained as follows : Volatiliz
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