58 THE MICROSCOPE. 



minate the object. The illuminator above described is placed in the 

 secondary stage, ii, which is situated below the general stage of the 

 microscope, and consists of a cylindrical tube having a rotatory motion, 

 also a rectangular adjustment, which is effected by means of two 

 screws, / m, one in front, and the other on the left side of its frame. 

 This tube receives and supports all the various illuminating and 

 polarising apparatus, and other auxiliaries which are placed under- 

 neath the object. The tube and its frame are affixed to a dovetailed 

 sliding bar, k, which can be easily moved up or down, or taken off 

 for conveniently attaching the various apparatus. This sliding bar 

 fits into a second sliding bar, which by means of a milled-head screw, 

 moving a rack and pinion, regulates the distance of the apparatus from 

 the stage. 



Directions for Use, by Day or Lamplight. 



In the adjustment of the compound body of the microscope with 

 the illuminator above described, two important results are to be sought, 

 first, their centricity, and secondly, the fittest condensation of the light 

 to be employed. With regard to the first, place the illuminator in the 

 cylindrical tube, and press upwards the sliding bar in its place, until 

 checked by the stop ; move the microscope body either vertically or 

 inclined for convenient use ; and with the rack and pinion which re- 

 gulates the sliding bar, bring the illuminating lens to a level with the 

 upper surface of the object-stage ; then move the arm which holds the 

 microscope body to the right until it meets the stop, whereby its cen- 

 tral 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, a, 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 object, and take off the cap of the eye-piece, 

 and in its place fix on the eye-glass called the " centering eye-glass," 

 described below, which will be found greatly to facilitate the adjust- 

 ment now under consideration, namely, the centering of the compound 

 body of the microscope with the illuminating apparatus of whatever 

 description.* The centering-glass, being thus affixed to the top of the 



* This centering-glass consists of a tubular cap containing two plano-convex lenses, 

 which are applied and adjusted so that the image of the aperture in the object-glass, 

 aud the images of the apertures at the lenses and in the diaphragms contained in the 



