ZOOLOGY AND BOTANY, MICROSCOPY, ETC. ].63 



MICROSCOPY. 



A. Instruments, Accessories, etc.* 

 3) Illuminatingr and other Apparatus. 



Lieberkuhiis.f— E. M. iSTelson writes that there is an old-fashioned 

 piece of apparatus which probably many microscopists have heard about, 

 but few seen in use ; the liieberkiihn. From the forties to the seventies 

 of last century lieberkiihns (which were called " cups ") used to be 

 supplied with their respective object-glasses, much in the same way 

 as they were in pre-achromatic times. 



Although they appear so very simple, both in theory and in 

 construction, they are, nevertheless, very tricky things to use ; therefore, 

 when anyone employs a lieberkiihn they should know how to get the 

 best results from it ; but the test-books may be searched in vain for 

 help or assistance upon this subject. It is probable that it was due to 

 the ignorance both of the method of employment and of the efficiency 

 of the lieberkiihn that it has fallen into disuse. 



With opaque objects in dry mounts, or not mounted at all, there is 

 not much difficulty, and the observer can hardly go wrong. For these 

 daylight, or artificial light by edge of flame parallelized by bull's-eye, 

 may be used from the plane-mirror. But it is with objects mounted in 

 a medium where the trouble comes in. Let us take an example : — A 

 spread slide of forams in balsam — objective 1 in. or 1^ in., with lieber- 

 kiihn. Now, first, it must be understood that there are opaque and 

 semitranslucent forams, and that each of these kinds will require a 

 different treatment. Let it be assumed that the lamp with attached 

 bull's-eye and plane-mirror have been set up in position ; then next it 

 is necessary to place a Lister's dark-well in the substage to stop out the 

 axial light. A Lister's dark-well consists of a piece of tube h in. long, 

 one end having a plug fastened to a stem by which it is attached to a 

 holder in the substage. The upper end of the tube should have a 

 sharp edge, and the inside of it should be blackened. Flat stops and 

 paper stops are not effective, because the lieberkiihn throws down a 

 good deal of light, some of which is likely to be reflected back again, 

 and this will spoil the dark ground ; but a Lister's dark-well, with a 



* This subdivision contains (1) Stands ; (2) Eye-pieces and Objectives ; (3) 

 Illuminating and other Apparatus ; (4) Photomicrography ; (5) Microscopical 

 Optics and Manipulation ; (6) Miscellaneous. 



t English Mechanic, Dec. 1, 1916, p. 370. 



M 2 



