142 
NOTES. 
[Under the head of Notes, it is intended in future to publish in the Journal , 
at the discretion of the Editor and Publication Committee, any brief and original 
communications that may be presented to the Society by our Fellows on the 
Construction of the Microscope, Microscopic Optics, subsidiary Microscopic Appa- 
ratus, and kindred subjects.— Editor.] 
Notes on Colour-Illumination , with Special 'Reference to the 
Choice of Suitable Colours . 
By Mr. Julius Rheinberg. 
( Bead 15 th February , 1899.) 
“ In the exhibition of objects in multiple colour-illumination before 
you this evening, I have endeavoured to keep two ends in view. The 
first was to have as varied a selection of colour-discs as possible; 
the second, to show as varied a set of objects as possible. The latter 
seemed to me the more important, and you will find on the tables 
specimens of physiological and botanical subjects, crystals, fibres, 
fabrics, insect structures, diatoms, living rotifers, &c., shown by the 
three different systems. 
“ The last time I had the honour of bringing colour-illumination 
before your notice, only two methods were available ; but since that 
time I have come across a third, which, to distinguish it from the 
high-power or diffraction method and the low -power or refraction 
method, may be conveniently termed the composition method ; it 
is equally applicable to all powers, and there is no restriction to the 
cone of light used, as in the first-named methods. It consists of the 
employment of a disc in the condenser, having preferably a red centre 
and a green rim, which, when the quantity of green is correctly 
adjusted by means of the iris-diaphragm to the quantity of red of 
the central spot, together form white light, so that, without an object 
in the field, the latter appears practically white. When an object is 
in the field, though the background is white, the different parts of the 
object itself do not catch the red and green light in the right pro- 
portion to form white light, and the object itself appears coloured, 
edges and prominent parts coming out in the green colour of the 
oblique green light thrown upon them, whilst small perforations and 
other less prominent parts which do not catch the more oblique light 
to the same extent, appear in red. 
“The reason a green disc with red centre is most suitable for 
this method of illuminating, is because the intensity of coloured rays 
entering the eye appears to vary with their obliquity. As the red 
part of the spectrum affects the eye so much more strongly than 
