I'm trying to remember a trick where performer used numbers 1 - 9, and 3 sets of colored balls. We'll use red, green and blue. Red may have been 1, 3, and 7, while blue would be 2, 4, 9 and green 5, 6, 8. Someone would throw the balls out into the audience, someone else would select the color pattern, i.e. RGB, and then a person with that colored ball would call out their number and so on until 3 three digit numbers where made. Those numbers would be added up and the solution found in a envelope. Does this sound remotely familiar to anyone?

John

Found it....

What was this effect called?

I can't recall the generic name for this type of effect, but one version was called Ultra Mentalism, and was featured in the Stevens on-line catalog over a dozen years ago. It was based the exact same principle, but used cards with four digit numbers printed on them. The people holding the cards would call out the digits in any order. This seemed to me to be much more deceptive.

Does anyone know a name for the principle involved here?

Murf

There are many, many versions of this basic concept. It's often called a "matrix force", though that can be confused with a "forcing matrix", which is quite another thing entirely.

Matrix Force sounds pretty good to me. My professors of 50 years ago would be dismayed that I couldn't think of the word matrix....

Murf

1665 force. Sum of a colored set is always 15.

Forcing 1665 is, however, but one simple example of a much more general principle (the matrix force).

Meir Yedid has a trick with large printed cards that works on the same principle' called Predict Perfect: http://mymagic.com/yedid.htm

Indeed, there are dozens of such applications of this force. Likely the best known is Jack London's original "Almost Real Prediction", of which there have been many variations. And Marc Paul spent a lot of time discussing this force in his recent Penguin lecture.