by Jolyon Jenkins

I think the answer lies not in ping pong balls but sponge balls. It will be obvious to the person pulling the balls out that they are sponge, but hopefully not to the rest of the audience, particularly if the balls are white and ping pong-sized. So although they are not everyday objects they may appear to be. The advantage of sponge balls is of course that they can be compressed into a very small space. Additionally, you will need a kind of ten-way change bag. Without actually making one it’s hard to know exactly what will work best but I think the principle is sound.

I suggest a padded cloth bag in a cylindrical shape (a kind of upright duffel bag ), with ten vertically-oriented load chambers build into the walls, all around the sides. Each load chamber would contain a dozen or so sponge balls each bearing same digit (probably stencilled on). Each chamber would be kept closed with a loosely sewn thread until that number is needed; then by removing the thread from the outside, the chamber will open and all the balls in it will be released into the main part of the bag, expanding and filling the bag. The magician having thus loaded the bag, the spectator will be forced to pick a ball with the correct digit. There then remains the problem of how to "remove" all the non-picked balls. I suggest that the bag should have a circular lid containing six stacked metal plates, the same size as the lid. When the lid is closed (to shake the bag) a plate can be released. The plate will fall to the bottom of the bag, compressing the sponge balls underneath it, and making the bag appear empty. The bag can then be loaded with the next set of balls.

As I say, there may be a simpler method of loading the balls and compressing them afterwards but I think the basic idea would work.