Revolver Immersion Prism. By James Edmunds. 35 



pas^sed without practical detriment, as only the edges of the beam 

 would become chromatized, or other angles may be given to the 

 revolver prism. If two such prisms were to accompany the Micro- 

 scope, one might be cut at angles of 25°, 30°, 35^, and 40°, in order 

 to light objects to be viewed under high-angled light in air on the 

 cover, or under low-angled light if in balsam. The second prism 

 might be cut at 40^, 45", 50°, and 55°, in order to liglit objects to 

 be viewed on the slide in air with black background, or under the 

 highest working angular apertures if in balsam. Difficult objects, 

 when set uj^on the slide in air for black-ground illuminatioi], re- 

 quire the cover to be very close down upon them, or they will not 

 be resolvable by high-angled lenses. 



