252 THE HISTORY AND DEVELOPMENT OF THE MICROSCOPE 



is fixed to the wooden basis of the instrument, and places for the 

 lenses are made in grooves beneath the hand- supports. The ad- 

 vantages of this general design have now been satisfactorily de- 

 monstrated by the large use that has been made of it ; but the 

 details of its construction (such as the height arid slope to be 



FIG. 203. Laboratory dissecting microscope (1870), 



given to the hand-rests) may be easily adapted to individual require- 

 ments. 



A very simple and well-known form of dissecting microscope is 

 made by Messrs. Bausch and Lomb. It is shown in fig. 204. Its 

 form is self-explanatory : a plain glass stage, and a mirror at a suit- 

 able angle giving abundant light, capable of being replaced by 



FIG. 204. Bausch and Lomb's (Barnes) dissecting microscope (1896). 



a white or black enamelled background, suitable rests for the 

 arm, and a sliding holder for the lenses. It is these latter that 

 are special : they are designed for the instrument. They are 

 doublets, which undoubtedly give a large aplanatic field and fine 

 definition. 



But the very best form of dissecting microscope for simple lenses 



