770 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



image should be free from spherical difference of magnification, by 

 satisfying the condition of sines, with respect to all the rays passing 

 through the space bounded by the two cones. Chromatic errors are 

 eliminated by the fact that the image is formed by reflection, not by 

 refraction. As will be seen from fig. 168, the author's condenser has 

 two reflecting surfaces, one internal, the other external. This tends 

 towards a complete satisfaction of the second and third conditions, and 

 the author claims that his condenser more fully satisfies these conditions 

 than any other yet brought out. The illuminating rays have a numerical 

 aperture of about 1*1 to 1*45. The reflecting condenser is contained 



Pig 170. 



in a centring mount, which slips into the sleeve of the Microscope sub- 

 stage in the place of the ordinary condenser. 



There is another and simpler form of this condenser mounted within 

 a plate, which is merely laid flat upon the stage of the Microscope 

 (fig. 169). This arrangement dispenses with the necessity of specially 

 adapting the reflecting condenser to the Microscope. By means of a 

 lever the condenser may be raised and lowered within the limits neces- 

 sitated by variations in the thickness of object slides. In conjunction 

 with an arc lamp of 4 amperes the condenser is sufficiently intense to 

 obtain an instantaneous photograph of living bacteria. 



Reichert's Drawing Apparatus.* — This apparatus, designed by 

 Bernhard, appears as in fig. 170. The drawing plane can be raised to 



* C. Keichert, Vienna, Catalogue, Mikroscope, No. 26 (1908) p. 61, fig. 63. 



