DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 103 



carry the condenser also, and in a manner the most effi- 

 cient for concentrating the light upon both opaque and 

 transparent objects. The condenser is represented at 

 m } in the same figures. 



SECT. 2. Spring -double- Stage. This stage, which is re- 

 presented at a, b t c, c, in fig. 24, is a vast improvement 

 upon the ordinary stages shewn in the previous en- 

 gravings, figs. 11, 12, and 17- It answers the purpose of 

 a safety-stage for large objects, mounted on a slip of glass, 

 or contained in a brass trough, or large live-box, which 

 must be placed between the stage-plate, , , and the 

 circular plate beneath it. This lower plate being kept 

 up by the two springs, c, c, allows the slider, trough, or 

 aquatic live-box, to be moved about in the manner re- 

 commended by Dr. Goring, in Chap. IX. The upper 

 plate, a, b, is furnished with a forked piece similar to that 

 shewn in figs. 13, 14, and has likewise a circular ring 

 for reducing its aperture when necessary. This stage 

 was contrived by me for making experiments with po- 

 larized light ; for which I consider that it, or something 

 like it, is indispensably requisite. 



It fits on to the microscope in the same way as do the 

 other stages, and like them may be furnished with dia- 

 phragms under it. 



SECT. 3. Moveable Stage. Various contrivances have 

 been made use of to give the stage of a microscope, when 

 an object is placed upon it for examination, a convenient 



