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Copyright Wet Paper Publications 2014
S
ECTION
1:
S
NORKELLING
PHYSICS AND
PHYSIOLOGY
Why do we see better underwater with a mask? What
makes us buoyant? Can pressure make us faint? This
section looks at some of the science behind
snorkelling underwater.
The physiological differences which the snorkeller
or diver must adapt to can be summarised under the
following headings:
The eye, the respiratory system, the ear, effects of
pressure, Boyle's law, the skin and buoyancy.
The eye
Light enters the eye through the lens, cornea, aqueous
humour and vitreous humour all of which bend the
light towards the retina (see Figures 1.1 and
1.2).
• The eye can focus light onto the retina by means
of a lens that can be contracted or relaxed by a set
of the ciliary muscles.
• The aqueous and vitreous humours maintain the
eye’s shape. The sclera helps maintain the eye’s
shape and is the outside covering of the eye.
• The retina has a set of light sensitive cells which
process dots of light that fall ono it. The retina then
sends information to the brain through the optic
nerve. Note that a blind spot forms where the optic
nerve leaves the retina.
Try the experiment described opposite to
demonstrate your blind spot.
Figure 1.1 Model of the eye
Bob Moffatt
To draw the blind spot tester on a piece of paper, make a
small dot on the left side separated by about 15 - 20 cm
from a small + on the right side.
Close your right eye. Hold the image about 60 cm away.
With your left eye, look at the +.
- Slowly bring the image (or move your head) closer while
looking at the +.
- At a certain distance, the dot will disappear from sight.
This is when the dot falls on the blind spot of your retina.
Reverse the process. Close your left eye and look at the
dot with your right eye. Move the image slowly closer to
you and the + should disappear.
Blind spot
Optic nerve
Sclera
Choroid
Retina
Ciliary
muscles
Muscle
attachment
Iris
Aqueous humour
Lens
Cornea
Vitreous
humour
Figure 1.2 Features of the eye affecting vision
Bob Moffatt
+
Blind spot
experiment
1 2,3,4,5,6,7,8,9,10