ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 659 



CHARLES CHEVALIER. About 1840. 



Type— Alternatively Simple or Compound : Achromatic. 



This exceedingly well made instrument is an enlarged and improved 

 Microscope upon the model of the preceding, embodying a number of 

 devices for use in an erect or in a horizontal position, and for the 

 observation of chemical reactions. It is described by its maker as his 

 " Microscope Achromatique Universel." The focusing arrangements, 

 both coarse and fine, are still attached to the stage, whilst the body 

 remains fixed. In the horizontal position a right-angled prism is used 

 for deflecting the rays into the tube. The mirror is plane and concave, 

 and is movable by rack-and-pinion. The whole Microscope is exceed- 

 ingly steady, and all the motions very smooth. 



Described and figured in Chevalier's " Des Microscopes et de leur 

 Usage," p. 88, pi. 4. 



HUGH POWELL. 1839. 



Type — Compound : Achromatic. 



This Microscope is of very great interest, because it embodies new 

 features which have now been very generally adopted in the design 

 of the Microscope. The body, stage, and mirror are carried by the 

 limb, which itself is attached by a compass-joint to an upright telescopic 

 pillar raised on a solid tripod. The coarse-adjustment by rack-and- 

 pinion for the first time moves the body of the Microscope, but the fine- 

 adjustment is applied to the stage by a wedge acted on by a micrometer 

 screw. In this model also Hugh Powell systematically applied the method 

 of " springing " in the movements to prevent loose action ; its application 

 to the pivots of the mirror can be well seen. 



Described in Journ. R.M.S., 1901, p. 728. 



HUGH POWELL'S Large Microscope. 1841. 



Type — Compound : Achromatic. 



This Microscope is one of three which the Council of the Micro- 

 scopical Society of London, soon after its formation, ordered of the 

 three best makers of the day — Hugh Powell, James Smith, and Andrew 

 Ross. This almost too elaborate and substantial stand was considered 

 the best of its day, and embodies all the most refined movements and 

 apparatus the maker was able to devise. The body is moved by rack- 

 and-pinion, and is attached to a hollow triangular bar. The fine- 

 adjustment actuates the stage. Originally this was a monocular 

 Microscope, but the binocular body with Wenham's prism was fitted to 

 it after the invention of the latter in 1863. 



Described and figured in Journ. R.M.S., 1900, p. 285. 



