114 



SELECTION AND USE 



principle, and so formed the under side of the stage in some of 

 his stands, that the object may be pressed against it by the 

 clips, which for this purpose are pushed through from below 

 upwards. In focussing, the objective is passed through the 

 stage if necessary. Great obliquity, and perfect safety against 

 breakage of the object by the objective, are secured. When the 

 microscopist is using valuable slides, costing from ten to one 

 hundred dollars, the latter feature is one of great importance. 

 In many microscopes, however notably those of English 

 manufacture the under side of the stage is not flat and even, 

 so that a slide cannot be laid against it. The following simple 

 device obviates this difficulty : A rectangular plate of metal is 

 pierced with a hole of the same size as the interior diameter of 

 the sub-stage ring of the micro- 

 scope, and in this hole is fastened 

 a tube, which just fits this sub- 

 stage ring. The plate is provided 

 with two light spring clips, which 

 hold the object against its under 

 side, and it is easy to see that this 

 simple contrivance which is shown 

 in Figure 26, serves three very im- 

 portant functions : 1. It affords 

 means for obtaining light of great 

 obliquity, since in reality it forms 

 a stage which has no thickness at 

 all. 2. It serves as a perfect safety 

 stage. 3. It enables us to rotate 

 the object very nearly in the optic 

 axis of the instrument. 



The rotating clips employed in the New Working Microscope, 

 also serve the same end, since they may be applied to the under 

 side of the stage quite as well as to the upper one, a groove 

 being provided for this purpose. 



Sub-Stage. The sub-stage is used chiefly for holding and 

 adjusting illuminating apparatus beneath the stage, and may 

 justly be regarded as one of the most important parts of the 

 stand. 



Fig. 26. 



