, and when it is used in connection
with the chlorophyl from dried leaves the plates are as sensitive to red
as can be safely prepared and developed in the light of an ordinary
photographic "dark-room." Plates prepared with chlorophyl from fresh
leaves do not require treatment with the tea organifier to secure this
degree of sensitiveness. Recently I have used the tea organifier and some
other sensitizers, in connection with the solution from _fresh_
myrtle-leaves, and in this way have produced plates having such an
exalted color sensitiveness as to be unmanageable in ordinary "dark-room"
light. Possibly, such plates might be prepared and developed in total
darkness, by the aid of suitable mechanical contrivances, but I am not
sure that they would work clear even then, because they appear to be
sensitive to heat as well as to light.]

My color-screen consists of a small plate-glass tank, having a space of
3/16 of of an inch between the glass, filled with a solution of
bichromate of potash about one grain strong. I place the tank in front of
the lens, in contact with the lens-mount. The advantage of this tank and
solution is that it can be more easily obtained than yellow plate glass,
and the color can be adjusted to meet any requirement.

The plates require about three times as much exposure through the yellow
screen as without it, and may be developed with the ordinary alkaline
pyro-developer.

[Illustration: IVES' PROCESS OF ISOCHROMATIC PHOTOGRAPHY.]

In order to illustrate the value of this process, I made two photographs
of a highly-colored chromo-lithograph, representing a lady with a bright
scarlet hat and purple feather, a yellow-brown cape and a dark-blue
dress. One, by the ordinary process, represents the blue as lighter than
the yellow-brown, the bright scarlet hat as black, and the purple feather
as nearly white. The other, by the chlorophyl process, reproduces all
colors in nearly the true proportion of their brightness, but with a
slight exaggeration of contrast produced purposely by using a too-strong
color solution in the small tank.

I also made two landscape photographs, one by the ordinary process, and
the other by the chlorophyl process, exposing them simultaneously. In the
ordinary photograph, distant hills are lost through overexposure, yet the
foreground seems underexposed, and yellow straw-stacks and bright autumn
leaves appear black. In the chlorophyl photograph, the distant hills are
not o