1^2 Modern Microscopy 



the pinion itself, holding the body meantime, or it will run 

 down on to the stage. 



Eemove the body from its fitting, wipe both bearings and 

 the rack thoroughly with paraffin-oil and a clean rag, then 

 dry them with another cloth. Now drop on, at most, two 

 drops of watchmakers' oil on each side of the bearing 

 fittings attached to the body, and replace the tube in its 

 fittings. It should then be moved up and down until the 

 motion is quite free, and if there are adjusting screws, they 

 should be so set that there shall not be any shake in the 

 fitting of the body, but that it may just, and only just, 

 move in the bearings with its own weight when the instru- 

 ment is set vertically. Carefully wipe the pinion leaves 

 out, and then, after setting the ink-marks in correspond- 

 ence again, the pinion may be attached. This usually 

 has adjusting screws to the cockpiece, which push it 

 closer to, or allow it to remain farther from, the rack ; 

 these should be so set as to give a soft movement. It 

 is useless to attempt this procedure with a microscope that 

 never has worked well, but where an instrument has, 

 after use, become unsatisfactory in the mechanical parts, 

 it generally is found to answer. Practically the same treat- 

 ment is applicable to the mechanical movements of the 

 stage, but very great care is essential, lest either of the 

 plates becomes bent, an accident that is more easy of 

 occurrence than would be deemed likely. 



Objectives. — It is unwise for unskilled persons to un- 

 screw parts of microscopic objectives ; they are frequently 

 deranged by this means. If at any time it should, from 

 some cause or another, be necessary to unscrew them, an 

 ink-mark or small scratch should be made on each com- 

 bination, so that when put together again they can be 

 screwed up in the same positions as before.^ In many 

 objectives it will be noted that three or four little spots are 

 engraved in a line down the mount for the above purpose. 



After using an oil immersion objective, the oil must 

 be carefully removed from the front lens by wiping with 



