Image from the Biodiversity Heritage Library.
Contributed by Museum of Vertebrate Zoology, University of California, Berkeley.
| www.biodiversitylibrary.org
Transcription
the centers of the two eyes, when the eyes are directed forward
and converged upon a close object. I believe this angle is about
45 degrees.
The two eyes are about 1.25 inches apart (Archie) and from
his gape to the end of his bill is 2.5 inches. (About 32 mm. and
64 mm., respectively).
The article, Vision, in Encyc. Brit., 14th. Ed. by Sir J.H. Par-
sons gives the angles of the field of vision of (presumably) the
human eye around the point of fixation as: Outward, more than 90
deg., downward 70, inward 60, upward 50.
In the present instance we are concerned with the inward angle:
60 degrees, although it is not necessarily true that the road-runner
eye has, in this respect, the same characteristics as the human
eye. However, this note is only a speculation.
Putting Archie's constants in the form of a diagram, we have:
From this it will appear that with his eyes inclined forward at
a 45 deg. angle with the line joining them, the inner edge of the
field of view will intersect the axis of his bill at an angle A
which is about 15 degrees. (His gape is directly under his eyes).
The distance from the point midway between his eyes ( or what
is sensibly the same thing: his gape) to the point of intersection
of the inner edge of the field of view of his two eyes is:
D; equals one half the distance between his eyes times
to the cotangent of the angle of 15 degrees, or:
D = 0.625 cot 15 deg., in inches.
= 2.34 inches.
As his bill is 2.5 inches long, he can then see with both eyes
0.16 of an inch of the tip of it!
Images A small object in the tip of his bill, then, will have its image
on corresponding points of the retinæ of his two eyes. Hence, pre-
sumably, he will have binocular vision of it.
The field of view at that point, i.e. the binocular field of
view at that point (the tip of his bill) is a small lens-shaped
field like this:
From there on outwards to infinity it is enclosed within a cone
of the above form of cross section, having an angle of about 30
degrees. Outside of that field, at least geometrically, with his
eyes in this position, vision would appear to be monocular.
(This is all speculation and is too rough to base conclusion on).