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strike it on its upper surface and as little as pos- 

 sible on its lower surface. If the direct light from 

 the bull's-eye reaches the object, it destroys to 

 some extent the effect of the oblique illumination 

 from the mirror. Great care should be given to 

 this point, as it is very important. 



If all of these suggestions have been followed, a 

 great difference will undoubtedly be noticed in the 

 performance of the objective ; but if it still does 

 not come up to the standard, patience must not be 

 lost. The slightest change in the position of the 

 mirror, bull's-eye, or lamp, or a touch to the cor- 

 rection collar or micrometer screw, is sometimes 

 followed by astonishing results. The beginner 

 should sit down with the expectation that he will 

 fail at the first trial. At each succeeding trial he 

 can easily notice his improvement in manipula- 

 tion and a corresponding gain in the results. He 

 vshould be able to bring the performance of the 

 objective up to the claims made for it, if it has 

 come from the hands of a reliable optician and 

 should not rest until this is accomplished. 



The writer has often recommended sunlight 

 with generally successful results where ordinary 

 means of illumination have failed. The light is of 

 course intense and great care will have to be used 

 to modify it by properly using the mirror, but suc- 

 cess is often attained and then creates confidence. 



