118 THE MICKOSCOPE. [May, 



that the pinion works loose, and occasionally to such an extent 

 that the body drops of its own weight. Tightening screws are 

 provided to take up the play. In the Professional, American 

 Concentric, Universal, Physician, Biological, and Library micro- 

 scopes these are in the back of the pinion. In the Investigator, 

 Model, and Family microscopes, they are seen in the slide by re- 

 moving the body. 



In using a screw-driver, grind its two large surfaces so that they 

 are parallel and not wedge-like shape, and so it will exactly fit 

 in the slot of the screw-head. 



In inclining the stand always grasp it at the arm and never at 

 the tube, as in the latter case it may loosen the slide or tear off 

 some of the parts. 



When repairs or alterations are necessary, always have these 

 made by the manufacturers ; they can, from the system of dupli- 

 cated parts, not only do it cheapest, but best. 



To take Care of Objectives and Eye-Pieces. — It is as 

 necessary to keep these freefi'oju dust as the stand, in fact even 

 greater cleanliness should be observed. When indistinct, dark 

 specks show in the field, the cause may usually be looked for in 

 the field-lens, although sometimes in the eye-lens also. The dust 

 may be removed by a camel's-hair brush, but when this is not 

 sufficient use a well-washed piece of linen, such as an old, old 

 handkerchief. From its fine texture chamois skin is desirable, 

 but as it is fatty it should never be used until after it has been 

 well washed. 



The same method applies to cleaning objectives. Clean an 

 immersion objective invariably after it has been used, first by re- 

 moving the fluid by a moist linen, and then by using a dry piece. 

 Keep the objectives especially in a place where they are not sub- 

 ject to extreme and sudden changes of temperature, as the un- 

 equal expansion and contraction of glass and metal may cause 

 the cement between the lenses to crack. Also keep them from 

 direct sunlight. 



Screw them into the nose-piece and unscrew by grasping the 

 milled edge. 



Avoid any violent contact of the front lens with the cover- 

 glass. Usually the latter suffers, but it is as liable to occur to the 

 former. 



Above all, it should be made a rule that no one but the owner 

 handle the microscope and accessories. One person may be ex- 

 pert in the manipulation of one instrument and still find it diffi- 

 cult to work with another. 



The fine adjustment particularly causes the greatest difficulty, 

 as in some instruments it corresponds with the movement of the 

 nmicrometer screw, while in others it is contrary, and thus the ob- 

 jective as well as object are endangered. 



