The original puzzle
Three lights are in an isolated room. Three switches are in another isolated room. Each swith affects one of the lights. How
can one discover the three connections by visiting each room only once ?
As in Finding the Faulty Coin, this is a ternary problem,
and we are misled into a binary frame of mind
by the fact that a light is either on or off.
Finding a ternary solution is a question of discovering another facet of a light bulb,
not only of generating light but also of generating heat.
The process is now quite "elementary" (my dear Watson) -
Turn on switches 1 and 2, and a few minutes later turn off switch 2.
Light 1 will be lit, light 2 will be hot, light 3 will be cold.
This one is great for young children !
Unfortunately, it is not always easy to find a place to experiment the process,
but, with the help of the janitor, you might find a good place in the school.