JOURNAL 
OF THE 
ROYAL MICROSCOPICAL SOCIETY. 
AUGUST 1896. 
TRANSACTIONS OF THE SOCIETY. 
YII. — On an Addition to the Methods of Microscopical Research, by 
a new way of Optically producing Colour-Contrast between an 
Object and its Background , or between Definite Barts of the 
Object itself 
By J. RHEiNBEna (communicated by E. M. Nelson, F.R.M.S.). 
{Read May 20th, 1896.) 
Plates IX. and X. 
It is my privilege this evening to bring before your notice the 
results of a series of what I believe to be original experiments, under- 
taken by myself during the last few years with the object of pro- 
ducing certain colour effects with the aid of the Microscope. 
The immediate end in view was to cause an object, when viewed 
with an objective of any power, to assume any desired colour upon a 
EXPLANATION OF PLATES. 
Plate IX. 
N.B. — Figs. 3, 4, 5, 6 represent dark-ground illumination if the colour-disc, 
fig. 2 a, is supposed to be replaced by a dark-ground stop, fig. 2 h. The blue parts of 
the figures should then be taken as being black, i.e. devoid of light, and the red 
parts as representing the passage of white light. 
Fig. 1. — Various colour-discs. 
Fig. 2. — Illustrating the effect which a colour-disc a, or a dark-ground stop b, 
placed at the back of an objective, has on the image of structures of varying degrees 
of fineness. F, Complete Diffraction Fan. D, Dioptric Pencil. 1, 2, 3, Diffraction 
Pencil of 1st, 2nd, or 3rd order. 
Figs. 3, 4. — Colour-disc illumination with low powers. 
Figs. 5, 6. — Ditto, ditto with high powers. D, Colour-disc ; C, Condenser ; S, Ob- 
ject ; O, Objective ; G, Diaphragm ; B, Dark space. 
The dotted lines in figs. 3, 4, 5, 6 indicate the passage of light, but it should be 
noted that in figs. 4 and 6 refraction and diffraction by the object S cause an uneven 
distribution of the light above it, which could not be clearly shown in the diagram. 
Plate X. 
Four photomicrographs of Diatoms (from Patuxent River, U.S.A.), taken with a 
double-image colour-disc, under precisely the same conditions, excepting that the 
aperture of the illuminating cone from the condenser was gradually increased. A 
1 in. objective of *21 N.A. was used. 
1896 2 d 
