ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



242- 



of course, be acting similarly. The action, moreover, is continuous 

 during exposure, the red waves impressing their forms in the film at 

 the rate of 38,000 to the inch, and the blue at 52,000 to the inch. 

 Prof. Lippmann did not advance beyond the theory, but last year 

 E. Senior photographed a spectrum, and by the aid of collodion stripped 

 the film from the glass support. W. B. Randies imbedded this film in 

 paraffin and after cutting sections mounted them in Canada balsam. 

 Figs. 34 and 35 show the results under high-power magnification, 

 and are photo-micrograms of the red part of the spectrum in which 

 the alternate bands are distinctly visible through the entire thick- 

 ness of the film. Fig. 36 is a photo-microgram of the blue part of 

 the spectrum under the same magnification. The portion of the film 

 acted on by the blue light was not quite so thick as that of the red 

 owing to the difficulty of making a perfectly plane film. The strata of 

 the blue are, as they should be according to theory, much closer together 

 than the strata in the red. Thus it will be understood that, after 

 development and fixation, each part of the film will reflect only the 

 light whose wave-lengths exactly coincide with the impressions already 

 made in the film. 



(6) Miscellaneous. 



Ultra-microscopic Objects.* — A. Cotton and H. Mouton, in repeat- 

 ing the experiments of Siedentopf and Zsigmondy on the visibilty of 

 finely-divided particles in certain media, have found the following 

 arrangements very convenient for studying liquids. A very oblique 

 beam of light, diagrammatically represented in fig. 37, is projected on 



Fig. 37. 



to one of the sides of an oblique parallelopiped A B C D with rectangular 

 top and bottom faces, and reflected upwards from the base through the 

 object-slide and cover-slip. A thin layer of the liquid to be examined 



* Revue Ge'neralc des Science.*, xxiii. (Dec. 15, 19D3) pp. 1184-91 (G figs.)- 



