The Magic Wine Glass.—The holding of a wine-glass to a substance mouth upwards without its falling off, may be accomplished thus. Obtain a wine-glass with a very even edge (this may be done by grinding on a flat stone), a square of blotting-paper, and a piece of glass. About half fill the glass with water, place upon its rim the blotting paper, and then the piece of glass. Whilst pressing them closely down invert the glass. The blotting-paper absorbs some of the water, a partial vacuum is formed, and on holding the sheet of glass, the wine-glass will remain suspended, being held on by atmospheric pressure. (See Fig. 20.)
Fig. 20.
The Floating Needle.—The idea of making a needle float upon water at first sight seems an impossibility but it can be done, and that with comparative ease. Take a fine needle, and rub the fingers over it gently to grease it. Now lay it very carefully on a piece of thin tissue paper on the surface of the water, as shown. Presently the paper will sink, and leave the needle floating on the water. The thin coating of grease serves to protect the needle from actual contact with the water, and thus enables it to float. (See Fig. 21.)
Fig. 21.
A Glass of Water Turned Upside Down.—A tumbler is filled with water, a piece of paper laid on, and the surface and the tumbler deftly inverted, the atmospheric pressure being unable to enter the glass, the water is kept in, so long as the paper holds. The effect of the experiment is very greatly increased, if, instead of using paper, a piece of thin mica, cut to the size of the glass, is used. The audience cannot then discover what prevents the water from running out. Any gasfitter will supply a piece of mica.
The Inexhaustible Bottle.—This wonderful bottle, from which five separate liquids can be poured, owes its marvellous qualities to the application of the simple law of atmospheric pressure. It is made of tin, and encloses five internal cylinders, each of which has a tube from the upper end running into the neck of the bottle, and another tube from the lower end opening into the side. The cylinders are filled with different liquids—water, milk, tea, coffee, lemonade. Whilst the fingers are kept over the holes the bottle may be inverted, and nothing will run out. On opening the holes one by one the liquid may be poured out, according to the wishes of the audience, and greatly to their astonishment. (See Fig. 22.)