HOW TO WORK. 



To Set Up the Instrument. Draw the instru- 

 ment from the case by grasping the base, and free it 

 from dust. If it has draw tube, bring it to its stand- 

 ard length, which is indicated by a ring, by as little 

 of a screw motion as possible ; if the draw tube is 

 highly polished, its surface will be best retained by 

 observing the above precaution. See that the mirror 

 and largest aperture of the diaphragm are in a central 

 position in the optical axis. After being convinced 

 that the eye pieces are clean, place one into the tube ; 

 then remove the objectives from their cases and after 

 first having increased the distance between the stage 

 and tube by means of the milled heads of the pinion, 

 attach the lowest power to the nose-piece, by using 

 both hands, being careful that it is as near as possible 

 in the optical axis while screwing it on. Then incline 

 the body by placing the left hand upon the base and 

 drawing with the right hand upon the arm ; be care- 

 ful not to pull on the tube, as it may prove too heavy 

 a strain upon this or the fittings. Incline the body 

 of the microscope until the eye piece about reaches 

 the level of the eye, so that when an observation is 

 made the position is as comfortable as possible ; the 



