No. 56.— 1905.] PHOTOGRAPHY OF COLOUR. 
437 
Tlie oiie drawback to this Kromskop replica is that it is an 
intangible image, one that can be seen only with the aid 
of a delicately adjusted and expensive instrument, and 
that cannot be handled and dealt with after the manner 
of an ordinary lantern or stereoscopic slide. 
By a modification of the Kromskop principle Mr. Ives 
also produced a device by which, with three separate 
lanterns and coloured screens, he could throw similarly 
concentrated natural colour images on a lantern sheet. This 
particular device was, however, as a matter of fact, an 
adaptation only of Prof. Clerk Maxwell's original idea. In 
addition to being the inventor of the Kromskop " it 
should be mentioned that Mr. Ives also devised the 
construction of natural colour photographic transparencies 
in which their stained carbon films were superimposed 
upon one another, and which in fact represents the funda- 
mental principle upon which the examples submitted 
to you this evening are constructed. 
Another distinct and exceedingly ingenious application 
of the three-colour photographic system is associated with 
the name of Prof. Joly of Dublin. In this modification of 
the constructive principle the three essential primary tints 
are ruled in parallel lines of microscopic dimensions and 
interspace on a viewing screen. One of these coloured 
viewing screens has to be laid upon and carefully adjusted 
to a single positive that has been printed from a negative 
that was taken through an analogous but complimentary 
coloured ruled screen. We have consequently here the ad- 
vantage of the negative and the positive only being required 
for the composition of the natural colour picture. Very 
pleasing effects may be obtained in conjunction with this 
"Joly" trichromatic method, but at the same time the un- 
desirable prominence with which the lines of the ruled 
screens become visible when the subject is enlarged in the 
stereoscope or thrown on the lantern sheet militates much 
against its practical adaptation for the technically accurate 
portraiture of Natural History subjects. 
