Jo~ty—On a Method of Photography in Natural Colours. 155 
colour sensations. This is done by a second screen, which carries red, green, and 
violet lines to the same gauge as the taking screen. We apply this to the positive, 
and as we move it over the image, waves of every tint of colour appear till that 
position is reached where the red lines fall over the lined areas recording red 
sensation, and so for the others. The picture now suddenly appears in vivid 
colour and with all the realism and relief conferred by colour and colour 
perspective. 
Plate V. shows a photo-lithographic reproduction of four of such photographs 
in colours, the full size of the originals. The originals being transparencies show 
a greater richness of colour. The reproduction too does not aim at reproducing 
the minute structure in simple colours of the plates. This could only be observed 
by considerable magnification of the original. This was inevitable, but is to be 
regretted as the remarkable, indeed startling, experiment is denied to the observer 
of assuring himself by aid of a lens that the whites are composed entirely of vivid 
lines of red, green, and violet; the yellows of red and green; and that the com- 
binations of the three primary colours, together with the black of the silver 
deposit, afford all the tints, however subtle, or however complex; tints many of 
which are extra-spectral, as the pinks, purples, and browns. 
It is further to be remarked that the reproduction of the grained appearance 
of the plates by the artifice of printing a grating of black lines upon the pictures 
is not, of course, fair to the originals. For in the reproduction these overlie the 
less saturated colours and complex tints equally with the saturated colours, whereas 
it is involved in the photographic process that where complex colours act, or colours 
which are not saturated, the action being more uniform over the three sets of lines, 
will result in a more uniformly transparent surface. Thus, in the white upon 
the shawl of the photograph of an Irish peasant girl, there should be only the 
faintest grain, and also upon the high lights of the face, and upon the faces of the 
soldiers in the picture beneath, &c. In spite of these drawbacks the reproduction 
fully serves the purpose of showing the stage this branch of photography had 
reached at the time this communication was brought before the Royal Society, 
and my best thanks are due to the Royal Dublin Society for reproducing these 
pictures. 
The following particulars regarding these four pictures may be of in- 
terest :— 
The photographic plates upon which the negatives were taken were Lumiére’s 
panchromatic series, sensitive, as photographs of the spectrum show, down to 
the C red. Development was with metol and hydroquinone mixed. 
The “Irish Peasant Girl” is from a water-colour picture by Miss Steel of Dublin; 
reduced in photographing about one-third. The exposure was fifteen minutes, 
TRANS, ROY. DUB. SOC., N.S. VOL, VI., PART V. ye 
