CH. /.] MICROSCOPE AND ACCESSORIES. 27 



end and the stage. Grasp the objective lightly near its lower end with 

 two fingers of the left hand, and hold it against the nut in the lower 

 end of the tube. With two fingers of the right hand take hold of the 

 milled ring near the back or upper end of the objective and screw it 

 into the tube of the microscope. Reverse this operation for removing 

 the objective. B3' following this method the danger of dropping the 

 objective will be avoided. 



§ 44. Putting an Ocular in Position and Removing it. — Elevate 

 the body of the microscope with the coarse adjustment so that the ob- 

 jective will be 2 cm. or more from the object — grasp the ocular by the 

 milled ring next the eye-lens (Fig. 21), and the coarse adjustment or 

 the tube of the microscope and gently force the ocular into position. 

 In removing the ocular, reverse the operation. If the above precau- 

 tions are not taken, and the oculars fit snugly, there is danger in insert- 

 ing them of forcing the tube of the microscope downward and the ob- 

 jective upon the object. 



§ 45. Putting an Object under the Microscope. — This is so plac- 

 ing an object under the simple microscope, or on the stage of the com- 

 pound microscope, that it will be in the field of view when the micro- 

 scope is in focus (§ 46). 



With low powers, it is not difficult to get an object under the micro- 

 scope. The difficulty increases, however, 

 with the power of the microscope and the 

 smallness of the object. It is usually neces- 

 sary to move the object in various directions 

 while looking into the microscope, in order 

 to get it into the field. Time is usually 

 saved by getting the object in the center of 



the field with a low objective before putting TKf**" " a ~3B> 



the high objective in position. This is FlL - 3&- Triple nose-piece 



, . .,., . , . . or revolver for quickly chane- 



ereatly facilitated by using a nose-piece, or . , . ,. .* ., _ * 



" J jo r ln g objectives \Oueen & Co.). 



revolver. (See also § 118, Figs. 61-66). 



§ 46. Field or Field of View of a Microscope. — This is the area 

 visible through a microscope when it is ill focus. When properly lighted, 

 and there is no object under the microscope, the field appears as a circle 

 of light. When examining an object it appears within the light circle, 

 and by moving the object, if it is of sufficient size, different parts are 

 brought successively into the field of view. 



In general, the greater the magnification of the entire microscope, 

 whether the magnification is produced mainly by the objective, the 

 ocular, or by increasing the tube-length, or by a combination of all 

 three (see Ch. IV, under magnification), the smaller is the field. 



