ZOOLOGY AND BOTANY, MICROSCOPY, ETO. 
685 
under these conditions shows, according to the author, small grains and 
globules of fat, all giving the same colour as the| field. Margarine, on 
the other hand, shows on the reddish-violet field grains of a yellow to 
greenish-blue colour. These colours also occur if the butter is old 
and rancid or contains boric acid, milk-sugar, or salicylic acid. 
Fig. 105. 
Zeiss’ Attachable Mechanical Stage.* — This stage (fig. 106) is in 
principle similar to those designed by Mayall and later on by Reichert. 
Two sliding pieces are moved in two rectangular directions by the 
milled heads S, T, and their position is recorded on millimetre scales. 
The extent of the rack-and-pinion movement is 30 mm., that of the 
lateral movement 50 mm. 
(2) Eye-pieces and Objectives. 
Zeiss’ Achromatic Objectives, f — With the aid of the extended list 
of materials produced by the Jena Glassworks, many of the older types 
of achromatic lenses have been reconstructed so as to more completely 
eliminate the spherical and chromatic aberration than was formerly 
possible. 
In fig. 107 the objectives a l5 <x 2 , a 3 , are seen attached to the tube and 
focused with respect to the plane of the object o o. They are so mounted 
•• - 
* Zeiss’ Catalogue, No. 30, 1895, p. 95. f Tom. cit., pp. 22-4. 
