222 HOW TO SEE WITH THE MICROSCOPE. 



highest angled objective, and with this examine the 

 mount in the ordinary way and get a tolerable correc- 

 tion for the glass. Next, removing the object-glass 

 from the stand, couple it to the illuminator and screw 

 the whole to the nose-piece of the stand, using trans- 

 mitted light, as usual. Focus the objective. Now hunt 

 through the slide ; among the numerous scales will 

 probably be found one or two which, in order t^ bring 

 in focus, the objective will require to be withdrawn from 

 the cover slightly. In such a case the chances are that 

 that particular scale is nearer the cover, and if in good 

 condition may be selected for further operations. Next, 

 bring the lamp (a flat wicked one) towards the observer, 

 revolving the tube of the illuminator so that the lateral 

 .aperture shall be in proper position to receive the light 

 from the lamp, the latter being about seven or eight 

 inches distant, and the flame about the same height as 

 the aperture of the illuminator. Now grasp the little 

 knob connected with the interior glass disk and turn it 

 .so that light shall be reflected to the rear of the object- 

 ive; at the same time, and looking through the tube as 

 you catch the first glimpse of light, revolve simultane- 

 ously the main tube and also the little knob carrying 

 the glass disk, the object being to secure as great an 

 amount of light as possible. A little manipulation of 

 this kind ought to result in illuminating the object with 

 a horizontal (or nearly so) band of light. The next 

 step will be by a slight movement of the lamp, keeping 

 Its edge exactly towards the aperture, to endeavor to 

 make the band of light crossing the field as narrow as 



