No. 56.-190').] PHOTOGRAPHY OF COLOUR. 
441 
screen, and one and a half mmute with the blue one, or a time 
total of over twenty-one minutes. With the rapid progress 
that is continually being made in the improvement of both 
plates and lenses with regard more especially to their speed 
properties, it is likely that the time exposures hitherto requir- 
ed when working with coloured screens will be very material- 
ly curfcailed,and that natural colour subjects will be achievable 
with the camera with a facility and expedition little short 
of that which already exists with respect to ordinary mono- 
chrome photographs. 
As a matter of fact when open land or seascapes 
are concerned, allowing the employment of a large 
diaphragm aperture with the lens, exposures of a few 
seconds only have been found sufficient with the red or 
densest tinted screen. A camera, moreover, has been con- 
structed with three lenses and the diaphragms and screens 
so adjusted that all three of the exposures can be made 
simultaneously and what are practically instantaneous 
photographs representing all of the required colour elements 
secured by a single exposure. So soon as this more rapid pro- 
cess is extended and applied to such subjects as ordinary por- 
traiture and which, there is every reason to believe, will soon 
be realized, it may be anticipated that an almost complete 
revolution of the existing methods of photographic portrai- 
ture will be effected. Fair sitters more especially will un- 
doubtedly consider that they have a distinct grievance if not 
supplied with photographs in which every subtle shade of 
their marvellous '^creations" (I believe this is the right 
word for their head adornments) as well as those of their 
fair features are faithfully reproduced. 
The description of plates used for taking these three-colour 
process negatives — Cadett's lightning spectrum plates — are 
necessarily extremely sensitive to light, and have to be devel- 
oped in almost complete darkness or with a safety light screen 
placed in front of the usual ruby light. The printing and 
development of the final positive transparenciesmay be accom- 
plished altogether on the lines of ordinary carbon printing 
