Marvin & Milo

Seeing circles



Seeing circles


What you need:

Blu Tack

String about 1 metre long

Two 2p coins

Old pair of sunglasses



Stick the 2p pieces together with Blu Tack and tie the string to it to make a pendulum. Watch from about 2m away as it’s swung from side to side in a straight line.

Break the sunglasses in half at the nose, and put a lens in front of one eye, but look at the moving pendulum through both eyes. Swap the lens to the other eye and watch again.


Results & explanation

You'll see the pendulum moving in a circle or ellipse, instead of a straight line. When you put the lens in front of your other eye, you’ll see it moving in a circle in the opposite direction.

Sunglasses block some light, delaying signals from your eye to your brain. Normally you don’t notice, but when you cover only one eye, that eye sees the pendulum delayed with respect to what the other eye sees, so your brain thinks it’s moving in a circle.


See previous cartoons

Strength in sand

Speeding spinner

Pinhole peeking

Dry times

Potato puncture

Fruity floater

Matching movement

Bubbles squared

Solid visions

Bottled tornado

Facing pressure

Mushrooming marshmallows

Take the money

Bubble bounce

Bead fountain

Jam jar session

Sixth-sense toy

Strange attraction

Impossible tower

Sinking sugar

Freezing time

Liquid strength

Mirror magic

Polar opposites

Unbalanced balloons 

Unsliced ice

Free fluid

Heavy atmosphere

Dogged drifter

Remote detector

Free fall ride

Electric slime

Pressure fountain

See more on

Cookie Settings