18 The Microscope. 



from them as much as possible. You should either 

 replace every part of the instrument in the case, or 

 a far more agreeable plan have a glass shade which 

 will cover the microscope and its accessories, and 

 under which they may be quickly placed, and in 

 doing this the glasses themselves should never be 

 touched by the fingers. 



With all precautions, however, the observer may 

 find that the glasses do require cleaning. An old or 

 borrowed instrument may come into your hands, with 

 an evident indistinctness in its performance. If the 

 defect consists of a general paleness in the image, this 

 indicates that the object-glass requires cleaning ; while 

 large dark blots tell of dust on the eye-glass, and you 

 can prove it by seeing whether they move when you 

 turn the eye-glass round. You should proceed as 

 carefully as possible about the cleaning. Firstly, dust 

 the surface with a soft camel's-hair brush to remove 

 loose particles, then wipe the glass with either a very 

 soft piece of leather or silk handkerchief, and keep it 

 for that use only, shut up in a little box. You had 

 best unscrew as little as possible, and replace each lens 

 as soon as clean, lest you might forget its proper 

 position. 



Dust inside the object-glasses is difficult to reach, 

 but by holding the open end of the object-glass down- 

 wards, the camel's-hair brush generally removes it, or 

 a small pointed bit of wood may be required for press- 

 ing a piece of soft leather to clean near the edges of 

 the lens. But all this must be as gentle as possible, 

 and not to be done where it can be avoided. " Hard 



