630 



SUMMARY OF CUKRENT RESEARCHES RELATING TO 



desired. The change from the projection of opaque material to lantern 

 slides, or vice versa, is accomplished simply by turning the handle at the 

 *feide of the apparatus. The screen picture is 6 x 6 feet, while No. 3 gives 

 an 8 X 8 feet picture. 



Illumination for Distinguishing intra vitam Colour Reactions.* 

 N, A. Cobb remarks that in order to distinguish with accuracy among 



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 ..-■''corergiass 



'■• square 

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'con<ienser 



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Fig. 1. 



intra vitam colour reactions, it is necessary to be very particular about 

 illumination. The best optical arrangement tried is the use of one 

 apochromatic objective as a condenser for another apochromatic objec- 

 tive. The author has been using with success a 2 mm. as a condenser 

 for a 2 mm. or 1 • 5 mm. apochromatic objective. This allows of fine 

 colour distinctions being made. 



The use of an ordinary apochromatic objective as a condenser neces- 



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Fig. 2. 



sitates the use of a special object-slide, consisting essentially of a carrier 

 and two cover-glasses. The object is mounted between the cover-glasses 

 (fig. 1). The substage of the microscope should have a centring 

 arrangement and a rack-and-pinion or screw-focusing adjustment 

 (fig. 2). A little experience with an apparatus of this sort, in which 

 all known precautions are taken to remove colour from the optical 

 system, leads one to distrust the ordinary Abbe substage condenser 

 where fine distinctions are to be made between colours, especially if the 

 colours are of similar character. 



* Science, xlvi. (1917) p. 169 (2 figs.). 



