CHAPTER ' II 



LIGHTING AND FOCUSING ; MANIPULATION OF DRY, 



ADJUSTABLE AND IMMERSION OBJECTIVES ; CARE 



OF THE MICROSCOPE AND OF THE EYES; 



LABORATORY MICROSCOPES 



APPARATUS AND MATERIAL FOR THIS CHAPTER 



Microscope supplied with plane and concave mirror, achromatic and Abbe 

 condensers, dry, adjustable and immersion objectives, oculars,* triple nose- 

 piece. Microscope lamp and movable condenser (bull's eye or other form, 

 Fig. 60) ; Homogeneous immersion liquid, xylene, alcohol, distilled water; 

 Mounted preparation of fly's wing ( 79); Mounted preparation of Pleuro- 

 sigma (\ 88, 89) ; Stage or ocular micrometer ($ 103); Glass slides and cover- 

 glasses (Ch. VII) ; 10 per ct. solution of salicylic acid in 95 per ct. alcohol 

 (2 103); Preparation of stained bacteria ( 119); Vial of equal parts olive 

 or cotton seed oil or liquid vaselin and xylene ($123); Eye shade (Fig. 67); 

 Screen for whole microscope (Fig. 66, 68). 



FOCUSING 



| 68. Focusing is mutually arranging an object and the microscope so 

 that a clear image may be seen. 



With a simple microscope (I 12) either the object or the microscope or 

 both may be moved in order to see the image clearly, but with the compound 

 microscope the object more conveniently remains stationary on the stage, and 

 the tube or body of the microscope is raised or lowered (frontispiece). 



In general, the higher the power of the whole microscope whether simple 

 or compound, the nearer together must the object and objective be brought. 

 With the compound microscope, the higher the objective, and the longer the 

 tube of the microscope, the nearer together must the object and the objective 

 be brought. If the oculars are not par- focal, the higher the magnification of 

 the ocular, the nearer must the object and objective be brought. 



\ 69. Working Distance. By this is meant the space between the simple 

 microscope and the object, or between the front lens of the compound micro- 

 scope and the object, when the microscope is in focus. This working distance 

 is always considerably less than the equivalent focal length of the objective. 

 For example, the front-lens of a 6 mm. or % in- objective would not be 6 



