CHAPTER IV. 

 ACCESSORIES. 



HAVING made the reader familiar with the compound 

 microscope, its eye-pieces and objectives, we must now 

 consider those appliances which conduce 

 to excellence in microscopical examina- 

 tions, or which render the work more 

 easy and more quickly performed. It 

 must not be imagined, however, that the 

 possession of all the following accessories 

 is imperative for microscopical studies ; 

 far from it, as precisely the same effect 

 as that produced by the most costly ac- 

 cessory can often be obtained (with more 

 trouble) by very simple and inexpensive 

 means. 



In the first place, we may consider the 

 draw-tube, which is shown in Fig. 32. It 

 is supplied of considerable length to most 

 monocular microscopes, being cut down in 

 many binoculars. 



Into this draw-tube the eye-pieces 

 should be fitted, and the former then 

 becomes a means of increasing the ampli- 

 fying power of the combination. By 

 simply drawing out the tube the object is 

 thrown out of focus, and the objective has 

 to be carried nearer the object. This wonderfully alters 

 the relative distances of eye-piece and objective from 



