Igo THE NORTHERN MICROSCOPIST. 
made to stand out in bold relief like half spheres. Those usually 
considered easily resolvable only require one pencil of light to show 
the markings. When this is the case, the rectangular arc-piece 
with all its illuminating apparatus can be turned away from the 
microscope stage as shown in Fig. 34. The same illustration 
Fig. 34. 
shows how opaque objects may be illuminated, viz., by moving the 
condenser of the first arc-piece above the stage of the microscope, 
when a pencil of light can be projected on to the object more 
perpendicularly than with the bull’s eye condenser, thus preventing 
shadows in coarse or deep objects which often produce distortion 
and false appearances. When the apparatus is used for opaque 
objects with a lower power than the 1-inch objective, the achro- 
matic combination can be removed and the light directed from the 
prism, which can be made to give convergent rays sufficient for use 
with a 4-inch objective. 
HOW TO PROCURE AND MOUNT RAPHIDES. 
By S. A. WEBB. 
S a handsome slide of raphides is always attractive, I give the 
following process for obtaining and mounting them :— 
The hanging plant known as “Spider-wort” ( Zradescantia) 
contains myriads of these needles. Place a slide upon the turn- 
table, cut off the vine or stem of the plant transversely (somewhat 
