Staunton spectator and vindicator. [volume] (Staunton, Va.) 1896-1916, 1910-05-20
EYES OF MEN. BIRDS AMI. IN
SECTS,


Mans eyes at rest are far focused
will make no effort when seeing the
moon or earthly horizons. Birds and
fishes eyes at rest are near focused
will make no effort when looking at
nearby worms and minnows. Mans
elastic lenses are under constant fiat
tening compression. Imagine a rub
Der ball of fiattened convex, lenslike
shape, laid in between two disks OF
canvas, and the uniting-edges of these
cloths, stretched to ring. They
would flatten the rubber. and il re-
Taxed it would thicken by its own
elasticity. The thicker the lens the
shorter it's focus. For reading or
threading needle we relax the ten
sion on the lens by contracting ring
of muscle surrounding each lens, and
then wait for the lenses to thicken
through their elasticity. In fish the
lens is set against the cOrnea Tap
proximately) short focus, and when 1t
wants to see whether the shadowy
object some feet away is shark or
log, it pulls the entire round lens to-
ward the retina, and gets as clear
vision as possible. Now we see why
so many human beings need spec
tacles'' as they grow old-the elastic
ity of the lenses is gradually lost, just
as it is in rubber. One more method
of getting focus is employed by the
eyemaker, which is dealt to some
snakes. Their lenses. which are set
near the retinas, are pushed forward
after the manner of pump piston, by.
blood pressure. Cheap eyes for cheap
creatures. Focus regulated by excite
ment
Some of the "eyes that can see in
the dark" have no power of changing
focus; so it makes no difference
whether they get might edition of
the days doings or not There is a
prevailing they say opinion that
birds sight is keener than mans
This is probably not true, as only man
and the simiae, which have parallel
vision,' possess a highly concentrat-
ed sensitive area in the retinas-
macula Utica.
But birds aloft are in clearer air
than man, and their eyes can change
focus with remarkable speed, as
necessitated by rapid fight. Birds OF
prey have voluntary Subject to the
IL n
/. in their irides. and can increase the
conveXity of the cornea and its re-
fractive power. Who has not wond-
cred how sparrow-hawk could dart
through brush and trees and never
turn feather by collision? Man with
his flying machines will be in sore
need of bird focusing speed.
We can see the single eyes of some
Gust. In viewing the house-fy we
need a lens. The big, visible, bulg.
ing eyes We see are composed of thou
sands of unit, cone-shaped eyes bound
or less spherical shape. Under lens
they look like glass-eyed pavement
bent to convexity. Their faceted cor
meas are variously set in square, hexa-
gonal or prismatic frames. Each
glistening facet is the cornea lens of
a distinct, self-working eye. Their
number in each compound eye is enor-
nous. There are so such eyelets in
each in the ant. 400 are allowed the
drone bee, and $500 the workers.
Our pet kitchen fly has 5000 chances
of seeing food crumbs, the beetle over
5000, while more than $4,000 aid the
dragon-fy in his eleemosynary pur-
suit of the mosquito, Offset somev haI
by several thousand awarded the lat
ter for sporting chance" The hawk
moth gets pictures compounded by
10000 contributors. Over $4,000 win
dow the brain of the mordella (beetle)
and 6J.000-so it is claimed-contrib-
ute to the happy lives of some butter
fiies.-Dr Edward A. Ayres in Har-
I per's Magazine.