44 THE MIOKOSOOPE. 



whose milled head is seen at N, and the fineness of which 

 is tripled by means of the lever through which it acts on the 

 object-glass. The instrument is of course roughly adjusted by 

 the rack movement, and finished by the screw, or by such 

 other means as are chosen for the purpose. One very inge- 

 nious contrivance, but applied to the stage, instead of the 

 body of the microscope, invented by Mr. Powell, will be found 

 described in the 50th volume of the Transactions of the So- 

 ciety of Arts. 



The greater part of the directions for viewing and illumin- 

 ating objects given in reference to the simple microscope are 

 applicable to the compound. An argand lamp placed in the 

 focus of a large detached lens so as to throw parallel rays upon 

 the mirror, is the best artificial light; and for opaque objects 

 the light so thrown up may be reflected by metallic specula 

 (called, from their inventor, Lieberkhuns) attached to the ob- 

 ject-glasses. 



It has been recently proposed by Sir David Brewster and by 

 M. Dujardin to render the Wollaston condenser achromatic, 

 and they have accordingly been made with three pairs of 

 achromatic lenses instead of the single lens before described, 

 with very excellent effect. The last-mentioned gentleman has 

 also projected an ingenious apparatus, called the Hyptioscope, 

 attached to the eye-piece for the purpose of erecting the mag- 

 nified picture. 



The erector commonly applied to the compound microscope 

 consists of a pair of lenses acting like the erecting eye-piece of 

 the telescope. But this, though it is convenient for the pur- 

 pose of dissection, very much impairs the op- 

 tical performance of the instrument. 



For drawing the images presented by the 

 microscope the best apparatus consists of a 

 mirror M (Fig. 23), composed of a thin piece 

 of rather dark-colored glass cemented on to a 

 piece of plate-glass inclined at an angle of 45 

 in front of the eye-glass E. The light es- 

 caping from the eye-glass is assisted in its re- 

 flection upwards to the eye by the dark glass, j?ig. 23. 

 which effects the further useful purpose of 



