2. Cut the resistor lead and the remaining LED lead to the same length, and plug the assembly into the bulb socket of a AA Mini Maglite flashlight (you may have to rotate the assembly 180° to get the polarity right).
3. Stand in front of a mirror in a dimly lit
room and hold the LED against the skin on
the outside corner of your right eye while
turning your gaze toward your nose. If you
turn your head slightly to the right, you’ll be
able to use your left eye to see the pupil of
your right eye glowing red in the mirror (see
page 62). By changing the focus of your eyes,
you may be able to see blood vessels magnified by the cornea and lens in the right eye.
The largest of these vessels are about the
size of a human hair.
THE LIGHT SWIRLER
The Light Swirler (Figure E) is a device for
smoothly moving a bright light in your peripheral view to cast shadows of the blood vessels
and tissue surfaces on top of your retina.
Think of it as a kind of retinal scanner, revealing the unique pattern used in real retinal
scanners for identification purposes. This
technique was first described in 1819 using a
handheld candle. Our device will be a scaled-down version of an instrument described in
1926, which used an incandescent bulb. Again,
in our modern version, we’ll use an LED.
You can get a preview of what you’ll see
with the Light Swirler by covering one eye
and looking straight at a blank wall with the
other eye while you rapidly flash a focused
beam of light on the pupil from the side.
Done correctly, you will see a branching
pattern blinking on and off.
With the Light Swirler the view is considerably more dramatic and detailed — the shadows writhe around without the distracting
blinking, and you can even see the moving
shadow from the slight depression in the retina at the center of vision (the fovea) and the
texture of the surface at the back of the eye.
To make it, you’ll mount a small lazy Susan
MATERIALS & TOOLS
PVC ceiling fan pan box and round cover
Lazy Susan, 3'', square Rockler #28951
Putty knife, plastic, 4''
Battery holder, 2×AAA RadioShack #270-398
Slide switch RadioShack #275-0406
LED, white RadioShack #276-0017
Nuts and screws, #6-32, 1" ( 3), ¼" ( 9–11)
Pipe strap (optional)
Soldering iron and solder
Common hand tools
Hot glue gun and glue sticks
Dremel rotary tool with sanding drum and
cutoff wheel (optional)
between a putty knife and a ceiling fan pan
box so you can rotate the box from the back.
The pan box will contain the LED, switch,
and battery box.
1. Start by making the crank arm. I used an
electrical box bracket and a #6 screw and nut
to make a crank as shown in Figure F. This
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