18 Mr. W. Saville-Kent on 
colour printings or positives from these negatives having a 
corresponding but complementary colour ratio. 
The scientific principle upon which the very remarkable colour 
reproductions now obtainable have been rendered possible owes 
its origin to the late Professor Clerk-Maxwell, who so long since 
as the year 1861 demonstrated the fact that all the colours of 
the solar spectrum, and concurrently all those of nature, are the 
equivalents of an admixture in varying proportions of the three . 
primary colours of the spectrum, viz. red, green, and blue-violet. 
It is only of late years, with the perfecting of photographic 
apparatus generally, and of plates and emulsions of extreme and 
discriminating sensibility in particular, that Clerk-Maxwell’s 
discovery has been found capable of practical commercial appli- 
cation. Among those who have contributed most extensively to 
both the theoretical and practical utilisation of this three-colour 
photographic process, the names of our own countryman, Captain 
Sir William Abney, Frederick E. Ives, of Philadelphia, Prof. 
Joly, of Dublin, and Lumiére, of Paris, are most eminently 
notable. 
The outcome of Mr. Iyes’s experiments and investigations has 
more especially been the production of that very ingenious in- 
strument the photo-chromoscope, or kromskop, as it is more 
popularly known. This is a contrivance by which, through the 
medium of accurately regulated red, blue, and green-coloured 
glasses and reflectors, photographs of objects previously taken 
through screens of the same tint are presented to the eye—more 
especially in the stereoscopic modification of the instrument— 
with the most realistic fidelity. Mr. Ives has also invented a 
kromskop lantern, by which, through coloured glasses, similar 
realistic images can be projected on a screen. The one draw- 
back, however, to these nature-like pictures as produced in the 
kromskop, or with the aid of the kromskop lantern, is that they 
are after all only intangible images that cannot be presented 
without the aid of the complex and costly instruments devised 
by their inventor. To meet popular requirements and general 
application, natural colour pictures or lantern slides that are 
available, like monochromes of the ordinary type, for individual 
handling and examination, or for projection by any ordinary 
optical lantern, have been the desideratum. 
Substantial progress has now been made towards the achieve- 
ment of this much desired goal. Ives himself was among the 
first to produce such tangible natural colour lantern pictures, 
the positives being printed on three transparent primary colour 
carbon tissues, which were then superimposed in correct register. 
Mr. Benetto, of Cornwall, from whom great expectations were 
in evidence a year or so since, has produced noteworthy results 
by the same process. Lumiére, of Paris, has employed stained 
