384 Transactions of the Canadian Institute. [Vol. VII. 



the eye. The transparency at C, being transmitted through yellow- 

 green and blue-green, reaches the eye as green. The red, green, and 

 blue-violet images are superposed on the retina, reproducing, in a very 

 faithful manner, the original colours. 



The writer was unable to obtain either a lantern attachment or a 

 Kromskop. The difficulty was overcome in the former case, as has just 

 been seen, by the use of three ordinary lanterns ; in the latter case by 

 constructing a modification of Ives' Kromskop. This differed in 

 principle by the substitution, for the coloured glass reflectors, which 

 could not be obtained, of transparent mirrors silvered on the front 

 surface. If unsilvered or uncoloured glass were used the reflected 

 imag-es would be doubled and registration could not be obtained. 



Fig. 6. — Diagrain ot the Kromskop. 



Considerable difficulty was experienced in getting a satisfactory film of 

 silver upon the thin plate glass used. It must be remembered that the 

 construction of a mirror, silvered on the front surface, even when the 

 coating is opaque, is by no means an easy matter; moreover that the 

 mirrors for the Kromskop require a transparent and uniform coating of 

 silver on the front surface, which must be of such density as to transmit 

 a definite proportion of the incident light, the quantity transmitted 

 being determined by the condition that the field of the instrument 

 remains uncoloured. Evidently the silvering process was not a simple 

 matter, and several trials were necessary. Success was, however, finally 

 obtained and the instrument constructed gives excellent results. 



The great objection to these methods of positive synthesis lies in the 

 fact that the colours can only be seen by means of special apparatus, 

 and although effects are produced by the Stereo-Kromskop, embracing 



