OF THE MICROSCOPE. 167 



vised, say one magnifying less than 100 diameters, move the 

 body of the microscope up, so as to increase the distance be- 

 tween the objective and the object. At the same time keep 

 your eye at the eye-piece and watch closely. At a certain point 

 the object will be seen with great distinctness; it is then in 

 focus, and is ready for examination. Always begin with low 

 powers. One of the greatest risks that the beginner runs is 

 that of breaking the objective by forcing it down on the object. 

 To avoid this with high powers, bring the objective down al- 

 most into contact with the slide; when doing this do not look 

 through the microscope, but watch the objective, and stop 

 whenever it is sufficiently near the object. Then apply the eye 

 to the eye-piece, slowly raise the body, and watch for the com- 

 ing of the object into focus. This is the only safe method with 

 high powers. 



Before attempting to place an object on the stage, or to re- 

 move one from it, see that the objective is raised at least half 

 an inch above the stage. By attempting to introduce a new 

 slide without raising the objective, when using high powers, 

 you run great risk of injuring both the object and the objec- 

 tive. And in removing objects from the stage, never lift them 

 up; always slide them off. In lifting them up, great danger is 

 incurred of bringing them into contact with the objective, and 

 thus doing irreparable injury. Sliding entirely prevents this. 



Where the microscope is not provided with mechanical 

 means for adjusting the focus, such as a screw or rack and 

 pinion, a great deal may be accomplished by special methods 

 of manipulation. Thus if, instead of pushing the body directly 

 through the collar, it be moved with a slightly twisting motion, 

 the focus may be adjusted with considerable delicacy, and when 

 the microscope is not provided with a fine movement, a great 

 deal may be done by means of a slight pressure of the fingers 

 on the stage. Few stages are sufficiently rigid to resist even 

 the slightest pressure. 



The chief points which the beginner should endeavor to 

 study are the variations which are made in the appearance of 

 the object by means of slight changes in the focussing and the 

 mode of illumination. Experienced microscopists constantly 

 keep their fingers on the fine adjustment of the microscope, 



