Ring Around
Two dark discs, one in a tight ring and one in a wide one.
How to play
Look first, then answer
Two dark discs, one in a tight ring and one in a wide one.
- Under a minute · one question · then the explanation
How it works — best read after you have tried it
Pulled out, pushed in
The discs are the same size. A ring close to a disc tends to be merged with it, so the disc borrows some of the ring’s size and looks larger; a ring far away is compared with it instead, and next to something big the disc looks smaller.
The Belgian philosopher and mathematician Joseph Delboeuf described it in 1865. It is a close relative of the Ebbinghaus circles, and it has been suggested that the same thing makes a portion of food look smaller on a large plate.