179 



arm which, holds the microscope body to the right, 

 until it meets the stop, whereby its central position is 

 attained ; adjust the reflecting mirror so as to throw 

 light up the illuminator, and place upon the mirror 

 a piece of clean white paper to obtain a uniform disc 

 of light. Then put on the low eye-piece, and a low 

 power (the half -inch), as more convenient for the mere 

 adjustment of the instrument ; place a transparent 

 object on the stage, adjust the microscope-tube, until 

 vision is obtained of the object ; then remove the ob- 

 ject, and take off the cap of the eye-piece, and in its 

 place fix on the eye-glass called the " centring eye- 

 glass," described below, which will be found greatly to 



FIG. 111. Beck's New Achromatic FIG. Ilia. Beck's Dry Achromatic 



Condenser. Condenser. 



facilitate the adjustment now under consideration, 

 namely, the centring of the compound body of the 

 microscope with the illuminating apparatus of what- 

 ever description. The centring-glass, being thus 

 affixed to the top of the eye-piece, is then to be adjusted 

 by its sliding- tube (without disturbing the microscope- 

 tube) until the images of the diaphragms in the object- 

 glass and centring lens are distinctly seen. The illu- 

 minator should now be moved by means of the left-hand 

 screw on the secondary stage, while looking through 

 the microscope, to enable the observer to recognize the 

 diaphragm belonging to the illuminator, and by means 

 of the two adjusting screws, to place this diaphragm 

 N 2 



