VERTICAL ILLUMINATOR. — STAGE-FORCEPS. 127 



flame should be seen upon the object. The Illumination of the 

 entire field, or the direction of the light more or less to either side 

 of it, can easily be managed by the interposition of a small Con- 

 densing Lens placed at about the distance of its own focus from the 

 lamp ; and slight alterations in its position will produce the effect 

 of the insertion of Diaphragms into the side aperture. The Objects 

 viewed by this mode of illumination must be uncovered ; since 

 if they are covered with thin glass, so large a portion of the light 

 sent down upon them is reflected from the cover (especially when 

 Objectives of large angle of aperture are employed) that very 

 little is seen of the objects beneath. It is specially applicable 

 to Diatoms, Polycystina, minute Foraminifera, and the Scales of 

 Lepidopterous and other Insects, viewed under Objectives of from 

 4-10ths to l-5th or l-6th of an inch ; and it often makes them 

 present appearances that would not in the least be suspected from 

 their ordinary aspect, when viewed as Transparent objects mounted 

 in Canada Balsam. 



Section 2. Apparatus for the Presentation of Objects. 



94. Stage-Forceps. — For bringing under the Object-glass in dif- 

 ferent positions such small Opaque objects as can be conveniently 



Fig. 75. 



Stage-Forceps. 



held in a pair of forceps, the Stage- Forceps (Fig. 75) supplied 

 with most Microscopes afford a ready means. These are mounted 

 by means of a joint upon a pin, which fits into a hole either in the 

 corner of the Stage itself or in the Object-platform ; the object is 

 inserted by pressing the pin that projects from one of the blades, 

 whereby it is separated from the other ; and the blades close again 

 by their own elasticity, so as to retain the object when the pressure 

 is withdrawn. By sliding the wire stem which bears the Forceps 

 through its socket, and by moving that socket vertically upon its 

 joint, and the joint horizontally upon the pin, the object may be 

 brought into the field precisely in the position required ; and it may 

 be turned round and round, so that all sides of it may be examined, 

 by simply giving a twisting movement to the wire stem. The other 

 extremity of the stem often bears a small brass box filled with cork, 

 and perforated with holes in its side ; this affords a secure hold to 

 common pins, to the heads of which small objects can be attached 



