THE MICROSCOPE 



323 



pound microscope are two : the object-glass and the lower lens 

 of Fig. 78, and the ocular or eye-piece and the upper piece of 

 Fig. 78. Both the object-glass and the eye-piece may, and 

 usually do, consist of more than one lens, for, as has been pre- 

 viously mentioned, better results are obtained by a combina- 

 tion of lenses of moderate power than by 

 single lenses of high power and great curva- 

 ture. 



8. How to Choose and Use a Microscope. 

 No attractiveness in the mechanical part of 

 a microscope can compensate for inferior 

 lenses ; and the very first consideration in 

 the choice of an instrument should be the 

 excellence of the optical part of the instru- 

 ment. In the use of the instrument, care 

 should be exercised to keep the lenses clean, 

 free from dust, not to press the object-glass 

 upon the object under observation, and not 

 to wet it in the water in which most objects 

 are examined. A good microscope requires 

 its own table ; and when not in use, should 

 be covered by a bell glass, or a clean linen 

 cloth. 



9. The mechanical portion of the instru- 

 ment varies greatly in different instruments. 

 That one is the best which is the simplest, 

 the most solid and most easily managed. 

 Most objects in human anatomy are exam- 

 ined in water or in other liquids, or they are 

 themselves liquids ; hence an oblique stage 

 is often inconvenient. 



10. Additional Apparatus. As almost all 

 objects in human anatomy are examined by 

 transmitted light thrown up from the mir- 



FIG. 78. COMPOUND 

 MICROSCOPE 



8. How to choose a microscope ? How to use it ? 



9. The characteristics of the best instrument? What special requisites should be 

 insisted upon f Why, as to a horizontal stape ? 



10. Slides ? Covers, square and circular ? How kept ? 



