ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



515 



when the mirror is inclined as mucli as it will ever need to be to the 

 axis of the Microscope, the whole of the surface of the lower lens of 

 the illuminator is covered by reflected light. 



Zeiss's Monochromatic Illuminator. — Dr. Zeiss supplies the 

 apparatus shown in fig. 96 for obtaining monochromatic light for 

 photo-micrography, or ordinary microscopic work. 



A glass globe 7 in. in diameter is held by the neck in a wooden 

 frame consisting of a base-plate, two uprights, and a cross piece. 



Fig. 96. 



The globe is filled with ammonio-copper solution, and placed in front 

 of the lamp, so that monochromatic light can be received by the mirror 

 or condenser. The space between the globe and the uprights is closed 

 by a thin wood screen, which also extends 5 in. upwards, and 3/4 in. 

 on each side of the uprights, shutting off extraneous light more 

 completely. 



The lamp intended to be used with the globe is a Siemens gas- 

 burner, and should be placed about 6 in. behind the globe, while the 

 mirror should be at the same distance in front of the globe. The 

 concentrated part of the rays should fall exactly on the mirror. It 

 will be remembered that Hooke * made use of a glass globe filled 

 with water as a bull's-eye condenser, and that Mr. Kitten, in 1881, f 

 also suggested the use of a globe filled with water as well as with a 

 dilute solution of sulphate of copper. 



* ' Micrographia,' 1665. 



t See this Jonrnal, i. (1881) p. 112. 



