OPAQUE OBJECTS. 



199 



The condensing lens, being placed near to the flame of the 

 lamp, must be arranged to throw parallel rays upon the re- 

 flector, which should be so adjusted as to condense them upon 

 an object placed in its focus. The manner of doing this is 

 shown by fig. 127, where A B represents the reflector, C a 



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Fix- 127. 



glass slide, supposed to be on the stage plate of the microscope, 

 with an object a upon it, L the lamp, the burner of which 

 should be on a lower level than the reflector, and D E the 

 condensing lens placed at a short distance from the flame of 

 the lamp ; the diverging rays given ofi" from it are rendered 

 nearly parallel by the lens, and the flve rays, r r, &c., faUing on 

 the reflector, become convergent as seen at r f, and, as such, 

 meet in a focal point on the object, a. The reflector being 

 attached to some immovable part of the microscope stand, and 

 the lamp and condensing lens being also fixtures, it follows 

 that the object, if large and flat, may be moved by the stage 

 adjustments into any position that may be required, without 

 the least alteration of the reflector; but, should the object 

 have an uneven siu:face, the reflector may then be so turned 

 on its ball and socket joint, as to suit every inequality the 

 object may present. Mr. Jackson attaches the reflector to the 

 compound body, so that the focal adjustment for obtaining 

 distinct vision, at the same time adjusts the light, as in the 

 Lieberkuhn. 



Lieberhuhn. — The mode of illuminating by perpendicular 



