120 



SELECTION AND USE 



power to be used is not very great. No person should attempt 

 to use high powers and complicated instruments until he has 

 served an apprenticeship by using a microscope of simple con- 

 struction, and objectives of considerable length of focus. 



Let the beginner commence by examining some transparent 

 object already mounted. To do this, set the microscope 

 on a firm table, in front of a window by day, or before 

 a lamp at night. Direct sunlight is to be avoided, the light 

 from a white cloud being usually preferred to any other 

 source of illumination. At night use a gaslight that does 

 not flicker, such as an argand burner, or a good kerosene 

 lamp, the German student lamp being very well suited to this 

 purpose. Good results may, howeveivbe obtained from any of 

 the ordinary lamps, especially those with a circular wick, which 

 are now so common. Very fair work may also be done by 

 means of a good candle. This subject has, however, already 

 been discussed at greater length in another section. 



If the microscope be a cheap French one, the objectives will 

 be found attached to the body, there seldom being any special 

 provision made for holding them. But with all American and 

 English microscopes, and the better class of instruments from 

 the continent of Europe, special boxes are provided for holding 

 the objectives. These boxes are usually made of brass, and 

 are indispensable to the microscopist that endeavors to take 

 good care of his instrument. Where the objective is kept in a 

 separate box, the body of the microscope must be raised to a 

 sufficient height, and the objective screwed into its place. In 

 doing this be very careful not to let the objective fall and strike 

 against the stage. We have seen more than one good lens 

 spoiled through such an accident. 



When the objective has been properly secured in its place, 

 move the body of the microscope up or down until the front 

 lens that is, the lens which is nearest to the object, is about a 

 quarter of an inch above the stage. Then turn the mirror 

 until the light from the window or lamp is reflected through 

 the microscope, so that when looking through it a bright cir- 

 cle of light is seen. 



Place on the stage some mounted object of large size, such 

 as a fly's wing or section of wood, If a low power objective b 



