146 
Notes , 
Table of Comparison of the Three Methods of Colour-Illumination. 
Method. 
Colour-differentiation 
dependent 
Available 
with 
Chiefly 
suitable for 
Cone of light 
from condenser 
used. 
Colour-disc 
placed 
Cone of light 
transmitted 
by central 
differentially 
coloured part 
oi the 
colour-disc. 
1st, referred 
to as high- 
power or 
diffraction 
method. 
Chiefly on 
diffraction. 
All 
powers. 
Medium 
and high 
powers. 
Narrow 
compared 
to objective 
cone. 
Above or 
between 
lenses of 
objective. 
Narrow 
compared 
to objec- 
tive cone. 
2nd, referred 
to as low- 
power or 
refraction 
method. 
Chiefly on 
refraction and 
reflection. 
Low 
powers. 
Low 
powers. 
Much wider 
than objec- 
tive cone. 
In sub- 
stage 
condenser. 
Equal or 
slightly 
exceeding 
objective 
cone. 
3rd, referred 
to as 
composition 
method. 
Chiefly on position 
and form of the 
different parts of 
the object, without 
diffraction playing 
any determining 
part. In excep- 
tional cases, 
however, wholly 
due to diffraction. 
All 
powers. 
. 
Medium 
and high 
powers. 
Any cone at 
will, greater 
than that 
passed by 
central spot 
of colour- 
disc, and not 
exceeding 
objective 
cone. 
In sub- 
stage 
condens r. 
According 
to circum- 
stances ; 
any cone 
less than 
objective 
cone. 
A list of the objects exhibited under multiple-coloured illumination 
will be found on p. 215. 
