8 AQUATIC MICROSCOPY FOR BEGINNERS. 



applies equally well to the use of the compound micro- 

 scope. 



To focus a pocket-lens, hold the object to be ex- 

 amined in the left hand, and, while looking through 

 the lens, raise and lower the glass with the right hand 

 until the magnified object appears clear and distinct, 

 the outlines sharp, and without a fringe of color, and 

 the surface rough or smooth, rounded or concave, as 

 it indistinctly appears to the unaided eye. The focus 

 cannot be obtained withd,ut this experimenting every 

 time the glass is used. A good plan is to place the 

 lens nearer the object than is known to be necessary, 

 biit always without allowing two to come in contact, 

 and then to raise the glass slowly until the image is 

 distinct, when it will be focused. Keep it steadily in 

 that position and study the object. 



The compound microscope {Fig. 2) consists of the 

 stand, the eye-piece, and the objective, although the 

 .word, as commonly used, refers to the entire combi- 

 nation of brass, with or without the magnifying glasses. 

 But without the objective the microscope is only the 

 "stand," and is practically useless. The stand alone 

 generally includes the tube or microscope-body, the 

 eye-piece (formed of two lenses at the opposite ends 

 of a short tube inserted into the upper end of the 

 body), the arm supporting the body, the stage on 

 which the object is placed to be examined, the mirror 

 to light the object, a movable circular plate, the 

 diaphragm, immediately beneath the stage, and the 

 foot that supports the whole. The addition of the 

 objective, or magnifying glass, at the lower end of the 

 body, makes the stand a compound microscope of the 

 simplest form. The objective is so named because it 



