ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



707 



with truncated rectangular pyramidal feet 8 mm. high at the corners ; 

 these feet are pierced by levelling screws. The slab is provided with 

 ear-like projections extending from either end through which the plate 

 may be screwed to small iron plates set into the floor. The upper 

 surface of the levelling plate is provided with stops against which the 

 base of the Microscope fits, with felt pads for the instrument to rest 

 on ; it has also a binding-screw by means of which a metal strip is 

 clamped across the base of the 

 Microscope to hold it to the plate 

 (fig. 138). To the end of the 

 plate at the back of the Micro- 

 scope is attached a socket from 

 which rises an iron rod 12 mm. 

 in diameter, and vertically ad- 

 justable by a thumb-screw in the 

 socket. At the top of this rod is 

 a cross bar 'for bearing a pair of 

 pulley-wheels, which may be set 

 at any point on 4 the backwardly 

 projecting limb of the cross bar. 

 An iron rod 11 cm. long and 

 5 mm. in diameter is attached to 

 one end of the axis of the pulley 

 by means of a Hooke's joint. 

 Supported from the wall by two 

 brackets alongside the camera is 

 a vertical metal rod which extends 

 from the level of the coarse- 

 adjustment screws to the upper- 

 most camera support (fig. 137). 

 This rod is provided with two 

 adjustable milled heads, which 

 may be set at any point so as to be 

 within easy reach. At the lower 

 end of the vertical rod is a third 

 bracket which supports a hevel 

 gear whose cog-wheels are each 

 about 3 cm. in diameter (fig. 138). 

 The upper wheel is attached to 

 the vertical rod, while to the 

 lower is attached, by means of a 

 Hooke's joint, an iron rod like 

 that attached to the axis of the 

 pulley-wheel, but only 3 cm. in 



length. When the levelling plate is in position these two iron rods 

 may be united by means of a brass sleeve in which there are two 

 screws (fig. 138). The Hooke's joints give this connection a certain 

 degree of flexibility, and so permit of considerable movement of the 

 levelling plate and of adjustment of the pulley-wheels on the cross bar. 

 When the connections have been made, the coarse adjustment of the 



Fig. 337. 



3 b 2 



