ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
397 
Light from the source A, incident at the polarizing angle on the first 
pile of plates B, is reflected to the second pile C, and thence to the 
mirror D. The two reflectors are fastened to the framo a a, which is 
firmly fixed to the foot b of the instrument by the binding screw c. A 
very slight turn of the mirror is sufficient to direct the unpolarized rays, 
represented by the punctuated lines in the figure, upon the object, so 
that the change from ordinary to polarized light and vice versa is very 
easily effected. 
Fig. 41 shows a similar arrangement made at the author’s suggestion, 
by 0. Behm, of Karlsruhe. The frame can ying the two reflectors B and 
Fig. 41 . 
C (each consisting of five large cover-glasses) is hinged to the edge of the 
object-stage E, so that for observation in ordinary light it may be swung 
back into the position B' C'. 
The arrangement shown F IG< 42 . 
in fig. 42, due to Voigt and 
Hochgesang, of Gottingen, 
is considered by the author 
as the most efficient. Bays 
from the source A fall upon 
the polarizing reflector B, 
and thence almost perpen- 
dicularly on an ordinary 
mirror 0 , from which they 
are reflected to the concave 
mirror D. Observation in 
ordinary light is effected 
by turning the latter into the position punctuated in the figure. 
The heating apparatus of the Microscope has been simplified. For 
ordinary requirements a burner with small non-luminous flame is used 
1891. 2 E 
