Indeed, the experiment will prove to you that, by so doing, you create in the bottle a partial vacuum, and as soon as your mouth leaves the neck of the bottle air enters it owing to atmospheric pressure. This incoming current of air pulls with it the cork, which at once slides into the aperture.
The same result may also be achieved by first warming the bottle, when, owing to the expansion of the air, a part of it is expelled. Directly the air inside the bottle cools, a vacuum is created, and a current of air from without enters. If you add to this current of air by blowing air from your mouth, you will find this quite sufficient to cause the cork to enter the bottle. Then, again, having a straw or a pipe-stem handy, all you have to do is to blow through the tube, directing the air exactly on the base of the cork, which will once again enter the aperture.
Whichever of these means is adopted, you must always take the precaution of seeing that the bottle is perfectly dry. It should be wiped every time. The moisture formed in the neck is sufficient to prevent the cork from gliding along the glass.
The Flying Coin
You may be inclined to think that special apparatus is necessary to make a coin fly from the bottom of a glass, but here is shown a very simple method by which the trick may be performed at any moment in your home.
First procure a liqueur glass of conical shape, having in its largest part a diameter not much greater than that of a silver dollar. At the bottom of this glass place a quarter, and above it, near the top of the glass, a silver dollar, the latter forming a kind of cover (A, [Fig. 2]). Now declare to your friends that, without touching the dollar, you will make the quarter jump from the glass.
Fig. 2.—The flying coin.
This at first seems to them an impossibility, but all you have to do is to blow very strongly on the edge of the dollar. This will make the larger coin turn about on its own diameter into a vertical position, whilst the compressed air under the quarter causes the latter to fly out of the glass, after which the dollar returns to its original horizontal position.