The Wonderful Pendulum
If you fill a wineglass with water and place a thick piece of paper over it so that no air can get in, you will find that you can turn the glass upside down without spilling a drop of water, because the pressure of the air on the outside will keep the paper from falling off. It is on this principle that the present pendulum is to be made. Take a piece of cardboard larger than the mouth of the glass; pass a cord through a small hole in the center of the card, and fasten it by means of a knot on the under side, then carefully cover the hole with wax, so that no air may get in.
Place your cardboard over the glass full of water, and by making a loop in the end of the cord you can hang the glass from a hook in the ceiling without any fear of its falling off. In order to make sure that no air can get into the glass, it is wise to smear the rim with tallow before laying the cardboard on.
The Revolving Pins
Take a piece of elastic which is not covered with silk or wool, and through the middle of this stick a pin, which you have bent as shown in the illustration.
Now hold the elastic between the thumb and first finger of each hand and twirl it round, stretching it a little at the same time. The rapid movement thus caused will make the revolving pin look like a glass object, and if you have a strong light falling on the pin and a dark background behind it, the resemblance becomes very much stronger.
After a little practice you will be able to represent many things in this way—cheese dishes, vases, champagne glasses, etc.; and if the bent pin should fall into a horizontal position while revolving, on account of its shape, you can tie one end to the elastic with a piece of white thread, which will not in any way interfere with the working.