Ch. I] 



OCULARS FOR THE MICROSCOPE 



27 



DENSER 

 -Sub5tag« 



§ 42. Equivalent focus. — Some opticians give the equivalent 

 focus of the ocular as with objectives (§ 19); then the user can select 

 with the same certainty as with 

 objectives. 



§ 43. Magnification of ocu- 

 lars. — The most recent method 

 is to mark upon the ocular the 

 increase it gives in magnifica- 

 tion to the objective (5X, lox, 

 etc.). If, for example, the real 

 image formed by the objective 

 is 10 times larger than the ob- 

 ject, and this real image is mag- 

 nified 5 times by the ocular, the 

 total magnification of the micro- 

 scope is 50. If the ocular mag- 

 nified 10, then the final image 

 would be 100 times the size of 

 the object, etc. By this method 

 the part done by the ocular can 

 be seen by inspecting the ocu- 

 lar. (For the method of de- 

 termining the magnification of 

 the ocular, etc., see Ch. IX.) 



The power of the ocular is 

 also indicated by the appear- 

 ance. A long ocular in which 

 the space between the eye-lens 

 and field-lens is considerable, 

 and the eye-lens is relatively 

 large is usually a low power 



(fig. 23) . If the ocular is short and the eye-lens relatively small, the 

 ocular has a relatively high power (fig. 24). 



For the mechanical parts of the microscope see fig. 25, and § 164- 

 166). 



Fig. 25. Laboratory Compound Mi- 

 croscope WITH THE Parts Named. 



Mirror, Condenser, Objective, Ocular 

 The optical parts of the microscope 



Tube-length This is the space between 

 the insertion of the objective below and 

 that of the ocular above. It is most com- 

 monly 160 millimeters. 



Mechanical parts These are named in 

 order from the base. 



