53 



neck should not be strained, neither should the chest 

 be compressed. Next place the slide with a transpar- 

 ent object upon the stage, by sliding it under the spring 

 dips and get it as near as possible in the center of the 

 opening ; for an object anything near at hand, such 

 as a piece of printed paper or cotton fibres will do. 

 Watching the slide, adjust the mirror until it is seen 

 that the light strikes the object ; incline the head to 

 the level of the stage, and observing the objective, 

 rack it down to within i inch of the object. Again 

 placing the eye at the eye- piece, reverse the motion 

 of the milled heads and observing the field continue 

 the upward motion of the body until the image of 

 the object appears in view. 



Centering Stage. If the microscope has a 

 revolving stage, turn this to see whether the object 

 or portion of it lying in the center of the field, 

 remains in the optical axis. It was true when the 

 instrument was shipped, but may have changed dur- 

 ing transportation. If not centered, loosen the screw- 

 holding it to the arm by means of the steel pin, just 

 sufficiently that by the exertion of a little pressure it 

 can be moved. After having observed first which por- 

 tion of the object remains stationary during its revo- 

 lution (this evidently is its center) move the stage so 

 that this point will be in the center of the field, and 

 then tighten the screw. If the point lies outside of 

 the limits of the field, its direction can be noted and 

 the stage moved accordingly. Where centering screws 

 are provided in the instrument, this is a simple mat- 

 ter. 



