ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



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head k) between the guides mm. A third plate carries a cylinder for 

 the ordinary cylinder-diaphragm. The diaphragm holder c d g is 

 attached to the bar t by the double elbow-piece h turning on a, so that 

 it can be brought out from under i, and the diaphragms (h) readily 

 changed. When in its place there is nothing to prevent a complete 

 revolution of the diaphragm-carrier by its milled rim, the elbow- 

 piece allowing the milled head e of the pinion / to pass without 

 obstruction. This is a third advantage claimed by the designer, 

 as the original form will not allow of this complete rotation. The 

 mirror by the addition of a simple contrivance could be made to move 

 obliquely. 



Either central or oblique illumination can therefore be used 

 without, as heretofore, having to remove the whole apparatus from the 

 Microscope and substitute a second form. 



Mr. T. Curties informs us that he has for some time constructed the 

 Abbe condenser so that it can be moved vertically beneath the stage. 

 This he accomplishes by attaching to the bar a tube-fitting t (fig. 14) 

 by means of which the condenser slides on the tail-piece of the Micro- 



FiG. 14. 



scope. A pin secures it in the optic axis. By this arrangement, 

 moreover, the condenser is readily applied to the simplest forms of 

 stands, which has long been a great desideratum. 



For the larger stands with rackwork substages he has been in the 

 habit of applying the same form of condenser, but without the tube- 

 fitting, rackwork being added to the bar. 



Some microscopists prefer Dr. Zeiss's modification for large English 



