The Birmingham age-herald., 1913-09-21
HOW FISH SEE
Anglers Instructed on Subsaqpeous
Optics and Range of Fish Vision

very interesting lecture was delivered
recently at Fishmenger's hall, London
Bridge, by Dr. Francis Ward. entitled
+ with a Camera Under Water" The lee
ture depicted subaquatic life from tho
fish's point of view, and was illustrated
by lantern slides and cinematograph
films There was a good attendance, and
the Earl of Portsmouth, who presided,
mentioned that the lecture was given un-
der the auspices of the Salmon and Trout
association, and they were indebted to the
Fishmongers company for the use of the
hall, says the Westminster Gazette
DR.. Ward assumed, for reasons which
he stated at length, that the vision of a
fish aproximated to our own, and pointed
out that the appearance of an object bo-
low water, and the way In which this va
ried in different situations was entirely
a question of subaqueous optics. The
angler could only learn what the fish
could see of him by placing himself in the
position of the fish. 1t was the anglers
business to keep out OF sight and to do
that he must learn the fish's range OF
vision. This varied with the depth OF the
fish in the water. Imagine the fish to be
three feet deep, the range of vision, look
ing upward, was through cone Of light
and surface circumference OF which was
u feet. In a room with a single window
an object held between the eye-of the OBJ
server and the window appeared as a sill
houette and with the fish every object
which came within the cone of light APP
peared as a silhouette against a bright
background.
The line of vision continued above the
surface of the water at a much wider
angle, SO that a fisherman standing on the
I,t
apparently right on top of him, while an
angler wading deep might be unobserved
though quite close to the fish. The arms
and rod would, however, be almost sure
to come within the view of the fish, hence
the advantage of deep wading lind OF
kneeling or lying on the ground when
throwing a fly over shy fish. Outside
the cone of light mentioned, vision did
not penetrate beyond the water, but oh
jects in the water outside the cone in
stead of appearing as silhouettes, assumed
their natural colors. and the surface OF
the water reflected exactly, aDd on calm
days reproduced the same co1ors as the
bottom. In the same way the under parts
of birds of prey acted as mirrors. When
a heron stood in the water making its
meal of fish. its legs looked like the stalks
of weeds, and the body with the murder.
Gus beal was quite invisible to tlle fish
until too late to escape. 4
me corinordHt' the guiis, the wafer nen,
and other birds which generally preyed
upon fish had wonderful powers of con-
cealment when under water, the most con-
spicuous birds on land appearing under
water as streaks of bright light, the
countless dir bubbles in even black
plumaged birds causing the bodies as
they passed rapidly through the water to
become mirrors rejecting the surround
ing colors. Thus, when hunting in green
weeds, the blackbird would appear green.
among brown rocks, brown, etc, with the
result that the general outline of the bird
would be hard to distinguish Fish had
also the power of changing color accord
ing to the environment. but directly a fish
turned off the even keel'its presence could
be detected and then 1t fell an easy prey
to its natural enemies.