Of THE MICROSCOPE. 27 



with several eye-pieces of different powers, which may be 

 changed at pleasure. We may here remark that where a mi- 

 croscope is furnished with several eye-pieces, the shortest eye- 

 piece gives the greatest magnifying power. 



The Cap is a cover which fits over the top of the eye-piece. 

 It is pierced with a hole, to allow the rays Avhich pass through 

 the instrument to reach the eye. This cap is sometimes covered 

 with a second cap, which has no hole, but which is intended 

 to exclude dust from the eye-lens, and which is removed when 

 the instrument is in use. 



The Mirror reflects the light, and causes it either to fall 

 upon the object or to pass through it, so as to render it 

 visible. 



The Mirror-bar is a bar attached to the stand and carrying 

 the mirror. It is usually made to turn on a pivot, and in the 

 microscope shown in Fig. 1, it consists of two parts sliding 

 tipon each other, so that it may be shortened or lengthened, as 

 circumstances require. 



Accessories are those parts of the microscope Avhich are used 

 only for special purposes, such as the paraboloid, the camera 

 lucida, stage forceps, etc. 



The Object is that which is subjected to examination. It is 

 usually mounted upon 



A Slide, or plate of glass, which is laid upon the stage. 



All these parts will be fully described in a siibsequent part 

 of this volume, and their utility and importance explained. It 

 is greatly to be desired that the young microscopist should 

 familiarize himself with the terms employed, so that he may 

 always use them accurately. Anything that he may say or 

 write will then be clearly understood by all who have given 

 careful attention to the subject. So important does the author 

 deem this matter, that he has in an advanced state of prepara- 

 tion an extended glossary or dictionary of microscopical terms. 



