This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
An interesting trick may be performed with three tumblers and three table knives. Place the tumblers in an equilateral triangle on a table so the knife ends, when the knives are laid between them, as shown in the plan sketch, are about 1 in. away from the tumblers. The trick is to arrange the knives so that they are supported by the tops of the three tumblers and nothing else. Most observers will say that it is impossible; some will try it and in most cases fail. It can be done, and the illustration shows how simply it may be accomplished. - Contributed by R. Neland, Minneapolis, Minn.
Ill: Knives Placed in Such a Manner as to be Supported by the Three Glasses