The Inclined Plane.
Reading edition
Take a piece of paper, roll it up into a tube large enough to hold a marble, and gum it lengthwise. Then introduce a marble and close the extremities with a strip of paper as shown below.
When you think that it is well dried you place it upright on the upper end of an inclined board, or flat ruler, leaning on a pile of books for example. You will then see the paper cylinder lie down, get up and so on till it reaches the bottom of its course.
The effect is very curious and will be more so if you are somewhat of an artist, and able to draw or paint a figure on the cylinder.