101 



be brought above the stage for this same purpose, 

 the results are not so satisfactory. The bull's-eye may 

 be used by interposing it between the mirror and 

 source of light, and with a very material increase in 

 its volume and easy regulation. 



Fig. 22. 



The Mechanical Stage, Micrometer, Camera Lucida 

 and other accessories have been treated separately, 

 and will therefore require no farther enumeration. 



