INTRODUCTION. 7 



the fingers, as finger marks are difficult to remove : no 

 matter how clean the skin, the oil from it will adhere to 

 the glass and can only be perfectly removed by wiping 

 with linen moistened with alcohol. 



When the lens is held in the hand to examine ob- 

 jects, rest the hand holding the lens on the hand hold- 

 ing the object. They will then tremble together. The 

 eye should be as close to the lens as possible in order 

 to obtain a wider field of view. 



In using the compound microscope the front only of 

 the objective and both surfaces of both lenses of the 

 eye-piece need cleaning. If the eye-piece be dirty there 

 will be specks in the field of view when there is no ob- 

 ject on the stage. These can be made more apparent 

 by turning the eye-piece in the tube while looking 

 through it. In like manner by partly unscrewing the 

 eye lens and turning it, it may be discovered whether 

 the eye lens or field lens is dirty. If the front of the 

 objective be dirty it will be manifested by a dimness 

 and want of definition of the outlines of objects, affect- 

 ing the whole field of view. 



In focusing with the high power of the compound 

 microscope, first rack the objective down as close to the 

 cover-glass as possible while watching it from one side. 

 Then look through the tube, rack slowly back and 

 watch for the coming of the object into view. 



Never rack downwards while looking through the 

 tube unless the object be in view. 



Do not use the fine adjustment until the object is 

 nearly in focus with the coarse. 



Raise the objective slightly before placing or remov- 

 ing a slide. 



