The Immovable Card
If a card, such as an ordinary visiting card, is turned down about a quarter of an inch at each end, at right angles to the rest of the card, and then placed on a table so as to rest on the turned edges, you may safely challenge most persons to blow it so as to make it turn over on the other side. It would naturally seem easier to overturn a card so prepared, than one whose shape remained unchanged; but whoever tries it will find that the facts are otherwise.
The card can be overthrown, however, by blowing on the table, toward the card, as the stream of air is then reflected against its under side.
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