The Oblique Illuminator 



271 



object illuminated as described above. When this is satisfacto- 

 rily done, a drop of oil of cloves is placed on the flat surface of 

 the hemispherical lens, which is then pushed up into contact 

 with the under surface of the slide on which the object is 

 mounted. The light now enters in the line of a radius of the 

 hemisphere, at the angle registered on the quadrant (7). Fig. 10 



represents a section of the ap- 

 paratus when thus in use (also 

 slightly reduced in size). The 

 numbers in the two figures cor- 

 respond. In addition, on Fig. 10, 

 A is the objective, B the slide 

 carrying the object, and C the 

 immersion fluid. 



I have found this apparatus 

 exceedingly convenient for the 

 purposes of pho- 

 to-micrography, 

 and sunlight worl 

 \ generally; for 



\ when I have once 



obtained any par- 



ticular result by 

 means of a certain 

 obliquity, I am able 

 to reproduce the ef- 

 fect at pleasure with- 

 out any loss of time. 



It has also proved useful, for the 

 same reason, by ordinary lamplight. 

 When, however, the object of the 

 microscopist is merely to resolve Am- 

 phipleura pellueida or similar tests 

 mounted in balsam, by lamplight 

 with suitable objectives, I still give preference to the simple sub- 

 stage prism I described last year (see Jouj-nal of the Roval 



