THE ROSS-ZENTMAYER STAND. 89 



quently receives the light without requiring altera- 

 tion of focus in any position of the bar ; by this means 

 facilities are afforded for the resolution of objects 

 requiring oblique light and for the development of their 

 structure. Rays are thus obtained in the readiest 

 manner possible from any angle, which is indicated by 

 a graduated circle round the eye or top of the swing- 

 bar, and many troublesome and expensive pieces of 

 sub-stage apparatus, before 

 used as specialities for ob- 

 taining oblique illumina- 

 tion, are dispensed with. 

 The value of this arrange- 

 ment was recognized, as I 

 have already stated, in 

 Grubb's "Sector Stand," 

 the movement of which 

 was obtained in a far less 

 efficient manner. Costly 

 high - angled condensers 

 may be dispensed with in 

 Ross's microscope, and 

 simple arrangements used 

 in their place, as Wen- 

 ham's immersion disc, or 

 the hemispheric lens. A 

 1^-inch or 2-inch object- 

 glass will generally suffice 

 for a condenser. This and other lenses can also be 

 used for opaque objects, by bringing the swing arm 

 and holder round above the stage, which it clears in 

 rotation. 



The base or stand of the Ross-Zentmayer instrument 

 is sometimes made in one piece, but preference will, I 

 believe, be given to the double pillar support, as this is 

 very firm, and allows the sub-stage to swing free, while 

 the microscope is in a vertical position, as in working 

 with fluid preparations. The rim of the sub-stage is 

 provided with set screws for centring the lenses used, 

 and, when determined, can be secured by a clamping 

 screw. 



FIG. 46. The Ross-Zentmayer 

 Student's Microscope. 



