the magnifier is required. Of this type Fig. 22 repre- 

 sents one of the most simple and inexpensive forms; 



Fig. 22. Barnes Dissecting Microscope. 



Fig. 23 a compact form in which all the parts may 

 be placed in the box which forms the base so that the 



Fig. 23. 



whole may be carried in the pocket, while Fig. 24 

 shows a form recommended by the highest authorities 

 for advanced work. 



20 



