ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



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a lens of 50 mm. diameter, and the third with a centring nosepiece for 

 two objectives. One of the condensers is nothing more nor less than a 

 microscope condenser of the usual type, whilst the other is a single lens. 

 The judicious displacement of these stands furnishes the means of 

 illuminating any of the microsummars of 24, 35, and 42 mm. focus, 

 objectives Nos. 1-9 and oil-immersion lens T V in. Microsummars 

 //4'5 are particularly adapted for low-power projection without an 

 eye-piece. 



Fig. 103. 



2. Diascopic Projection. — In this mode of projection the object- 

 stage U (fig. 104) should be swung aside. Having displaced the objec- 

 tives and eye-pieces, the lantern projection lens Q (e.g. aplanatic lens of 

 200 mm. focus) must be turned into the optic axis. The carrier itself 

 remains in its original position, the objective of 200 mm. focus only 

 requiring sharp focusing by means of the rack-and-pinion. The 

 lantern slide-carrier (figs. 104 and 105) is arranged to take two slides at 









once, one above the other, the lower one being that which appears on 

 the screen. The latter is removed in a downward direction, whilst the 

 upper one glides into its place so as to be projected in turn. The suc- 

 ceeding lantern slide is introduced from above, and the process repeated 

 as often as required. To facilitate the removal of the lower slide, the 

 optical bench is provided with an arched gap, so as not to impede the 

 motion of the hand, as may be seen from the figure. The holder of the 

 lantern slides is adjustable in all directions, so as to render it available 



