1947 was an interesting year for innovation in pinball. America was out of World War II, manufacturing was brought back to bear on amusement devices.
Exhibit came out with an interesting game called Treasure Chest, which contianed a player-controlled magnet! This used a flipper button on the side of the cab to turn the magnet off an on to (potentially) achieve higher scores.
Years and years before such magnets would make a resurgence in solid state games in the 80s, Exhibit put one at the bottom middle of the playfield.
Interesting artwork, good use of the theme (dive down and back with the treasure to score up to 30 replays!), and of course, the magnet make this a really neat game.