BLACK BACKGROUNDS. 
113 
the object. If the direction of illumination is at too 
wide an angle with the optical axis, much of the light 
will be totally lost by reflection. 
The next, and a better, method consists in the use of 
a “ side reflector,” such as is made by many opticians. 
An example is shown at fig. 29. 
This appliance should not be attached to any moving 
part of the stand, but to the stage or the limb of 
the stand, the reflector should remain steady, all but 
touching the preparation, and right opposite it, in a 
line at right angles to the optical axis, is placed the 
light, the rays from which should be directed in a 
parallel bundle through a bull’s-eye right on to the 
reflector ; from it the rays are reflected down upon the 
object, which is thus brilliantly illuminated. For this 
work also the exposure must be long. 
The reflecting device known as a “ Lieberkiihn ” is 
both very pretty as a scientific instrument and very 
valuable in use, but it necessitates a special mount, or 
a simple enough addition to an ordinary mount. The 
light is passed up from below in a parallel bundle round 
the object, falls on the polished front of the “ Lieber¬ 
kiihn,” and is reflected down from the latter on to the 
object. Fig. 30 shows the instrument, and fig. 31 shows 
the method of mounting objects for its use. The 
central part of the mount is blocked out, and this may 
be done in the mounting, or by the microscopist. A 
piece of court-plaster of suitable size may be cut out 
and fixed to the back of the glass slip behind the object, 
or another slip bearing the opaque spot may be placed 
