LOBB^ ON A NEW MICROSCOPE. 177 



L,, Upper stage^ with three quarters of an inch rectangular 

 motion by screw and pinion connected with tlie milled heads 

 7, 8, 9, the last not seen; this stage has a sliding plate and 

 spring clip for the objects^ also a clamp to fix it, and gradu- 

 ated scales to act as a finder^ in order to register any 

 particular object; the rotary motion of this stage is in con- 

 nection with milled head 10. 



M, Under stage, with rotary, rectangular, and vertical 

 motions ; milled head 10 for rotary motion ; milled heads 

 12 and 13 for rectangular motion ; milled head 2 for vertical 

 motion. 



N, Achromatic condenser of 170° aperture, the working 

 powers of which are admirable, easily resolving the Amician 

 test in squares Avith one twelfth and one sixteenth object- 

 glasses ; it has a diaphragm with eleven apertures and three 

 stops, capable of being placed in any position. 



The object of the makers in producing the present instru- 

 ment, was to make a microscope possessing a very thin stage 

 for the oblique illumination of the most delicate diatomacese 

 either by the mirror or prism, and at the same time to have 

 a rotating stage ; this desideratum they have accomplished in 

 a very satisfactory way, and all that possess the instrument 

 are much pleased with it, from the steadiness of its motions, 

 its freedom from tremor, and the convenience with which all 

 the milled heads for the various motions are placed. The 

 stand is like those usually employed by the makers, a strong 

 tripod, but made larger and heavier than usual to meet the 

 requirements of the other parts of the instrument, which it 

 bears with remarkable steadiness in whatever position it is 

 placed. The bar that carries the compound body, instead of 

 being triangular, is quadrangular, like that employed by 

 Mr. Ross, but not rectangular like his, it having two obtuse 

 and two acute angles; the makers consider this theoretically an 

 improvement, and practically I can say that nothing can be 

 steadier than this instrument is, even with the -r^th. object- 

 glass. The bar is worked as usual, with rack and piiiion, and so 

 nicely adjusted as hardly to require the fine movement with 

 the 4-- The head of the sIoav motion is graduated as in 

 Rosses, and Smith and Beckys. The bore of the body is l-i- in. 

 in diameter, which gives a very large field of view with the lower 

 eye-pieces ; it has a draw -tube, which is graduated to the 

 extent of four inches into tenths of an inch. The brass 

 circle which carries the motion for the rotating stage, is 

 firmly screwed to the main part of the instrument ; and at 

 the top is attached a circle of gun-metal, which is graduated 

 into 360" in quadrants ; an index is fixed to the stage move- 



