Directly you lower the level of the water, your friend will no longer be able to see the image of the coin, which will be hidden by the side of the bowl. If, however, the extracted water be replaced, the image of the coin immediately reappears.
Electrified Paper
Very few people realize that paper can be electrified at a moment’s notice, no special apparatus for the purpose being required.
Take a piece of light paper, which should have been well dried, and rub it briskly with a clothes brush, silk handkerchief, or even the open hand.
After a little time the paper, becoming electrified, will adhere to your face, your hands, or your clothes, as easily as if it were attached by means of gum.
Nor is this property confined to thin paper. Thick paper, when dried, will act in the same manner. For instance, take a postcard, dry it, and rub it, and you will notice that, as is the case with sealing-wax, glass, sulphur, &c., the card has the power of attracting light bodies, such as small pieces of cork.
The following interesting experiment may be carried out with an electrified postcard and a walking-stick.
Balance the walking-stick over the back of a chair, and announce that you can make the stick fall without touching it, without blowing it, or without interfering with the chair. This is easily possible by utilizing the electrified postcard.
Fig. 10.—The electrified postcard.