234 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
cases of colour-blindness and on account of tbe variation in colour 
sensation. 
Fig. 31 shows the external form of the simple half-shadow apparatus 
with wedge compensation, as specially constructed for urine analysis ; 
and fig. 32 shows the method of arranging the lenses. The advantages 
of Laurent’s half-shadow are larger dimensions, greater delicacy of 
reading, and better mechanical arrangement. 
; Fig. 31. 
In Lippich’s tripartition of the field of view, a much greater im- 
provement of the half-shadow results, securing a very high degree of 
accuracy. Whilst in the simple Lippich polariser only one sharp-edged 
so-called half-prism is placed before the large nicol, and the field of view 
bisected, in the tripartition system two of these sharp-angled. half-prisms 
are employed, as shown in fig. 30. The effect of this application is to 
produce as great an improvement in the wedge compensation as in the 
circular apparatus. 
With the Landolt-Lippich apparatus the investigation of substances 
in strongly heated or cooled media is possible (fig. 33). For such 
purposes a metal box with asbestos casing and an inner observation tube 
