Blackbox is a clever two-player deductive game invented by Eric Solomon in the 1970s. Your goal is to discover the whereabouts of five atoms in a black box by sending rays of light into the box and observing if and where the rays emerge. An atom will either absorb a ray if the ray hits it head on, or deflect a ray through 90° if it comes close (passes through an adjacent row or column). Two deflections can occur at the same time forcing a ray to return and emerge at its entry point, this is referred to as reflection.

Sorry, this is a Java applet.

The challenge is to pin point the location of all atoms using the least number of rays. If you wish to commit your solution and to discover your score you must have exactly five guesses marked, then click on Reveal. The five hidden atoms will appear marked as @.

Click New Game to generate another arrangement of hidden atoms.
Click Reveal to check you guesses and display the position of the atoms.

To activate a ray click on one of the edge buttons marked with a #.
To mark your guesses with a ? click on the unmarked central buttons.
To undo a guess just click on it again.

Your score will be 36 (the total number of ray buttons) minus the number of ray buttons used, minus 5 for each incorrect guess. Any score in double figures is good!

What happens in the box?
The diagram below illustrates how rays sent into the box interact with the atoms. Absorbed rays are labelled A. Reflected rays are labelled R (note that the two types of reflection (the brown and green rays) are indistinguishable). Rays which propagate through the box from one point to another (as with the red ray) have their entry and exit points marked with a unique number.

Red Deflected by atom a.
Purple Absorbed by atom a (direct hit).
Blue Absorbed by atom d rather than deflected by b (absorption overrides deflection when two atoms sit side by side).
Brown Reflected by atoms a and b (the ray is deflected by both atoms in turn so that it's path turns back on itself and emerges where it went in).
Green Reflected before entry by atom c (this is a special case of reflection).

Note that rays may be deflected several times before emerging from the box, or before being absorbed or reflected.

invented by – Eric Solomon (marketed by Waddingtons Games - 1976)
applet – © Andrea Gilbert 1997