powers which make up the usual outfit, and it is some- 

 times impossible to make them par focal. The 2-3 

 and 1-6 or 1-8 on the double nose-piece, and the 2-3, 

 1-6 or 1-8, and 1-12 oil immersion on the triple 

 nose-piece can be so made. But in a combination of 

 a lower power with the 2-3 and 1-6 on the triple nose- 

 piece, or a lower power with the 2-3, 1-6 and 1-12 on 

 a quadruple nose-piece, it is impossible to make the 

 lower power par focal with the others on account of 

 the considerably greater working distance. 



As the adjustment of the objectives to make them 

 par focal is quite delicate each screw in the nose-piece 

 should be marked to correspond with the power of the 

 objective which is to go into it. 



To focus with double nose-piece : 



Screw each objective into proper place in the double 

 nose-piece, with the 2-3 opposite the opening through 

 which the light passes. 



Hold the nose-piece in the right hand, objectives down; 

 bring the revolving screw in contact with the screw in 

 the tube, square with tube ; with thumb and forefinger 

 of left hand turn milled edge of revolving screw until 

 it engages ; swing nose-piece toward the front and, hold- 

 ing it in this position, screw the ring home. 



Focus with 2-j objective, then swing nose-piece 

 until 1-6 nears the cover glass ; lower the head to the 

 level of stage ; endeavor to slowly swing objective in 



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