Modern Magic: A Practical Treatise on the Art of Conjuring

The trick, as above described, is of very short duration. In order to lengthen, and at the same time to diversify it, a second ball is sometimes employed, of similar appearance, but of different construction. This second ball (see Figs. 137, 138, the latter representing a section of the ball) is a strongly made hollow sphere of tin or zinc, with a circular opening of about three and a half inches across, closed by a sort of sliding door, a, also circular, working on two curved arms, b b, which move on two pivots, c c, at opposite sides of the ball on the inside. In this door is a hole an inch in diameter, answering the same purpose as the hole bored in the solid ball.