APPENDIX. 347 



field-glass of the periscopic eye-piece. The amplifier re- 

 ferred to at page 26, or an achromatic concave meniscus, 

 is added to this form of eye-piece about three inches from 

 the field-glass. I find this to give better definition than 

 the amplifiers of Zentmayer and Tolles, which are placed 

 at the end of the draw-tube. 



IMPROVEMENTS IN ILLUMINATORS. 



Most of the improvements suggested in illuminators 

 have been connected with oblique light. In Amici's prism, 

 Nachet's prism, Reade's condenser, etc., the purpose is to 

 utilize oblique light and exclude central. In the illumi- 

 nator proposed at page 35 I have combined a condenser 

 with an illuminating prism. Mr. Edmunds (after Mr. 

 "YVenham) has contrived a paraboloid lens with the front 

 cut off flat and polished. This is in fluid contact with 

 the under side of the slide. Mr. Wenham's reflex con- 

 denser, although difficult to use, is capable of excellent 

 effects. A small lens (plano-convex) placed in immersion 

 contact with the under side of the slide is also used. Dr. 

 Woodward's prism, however, for effectiveness and cheap- 

 ness, bids fair to surpass them all. This is a small right- 

 angled prism, with its base in immersion contact with the 

 slide, receiving the light from the mirror or condenser at 

 right angles to the facet. 



The hemispherical condenser and oblique illuminator of 

 Mr. Gundlach, attached to the "Professional" microscope 

 of the Bausch & Lomb Company, are also well adapted 

 for the purpose. 



DOUBLE-STAINED PREPARATIONS. 



Sections of vegetable tissues present a beautiful appear- 

 ance under the microscope when doubly stained. They 

 should first be soaked in alcohol, if green, to deprive them 

 of chlorophyll, then subjected to a solution of chloride of 



