Here we are dealing with a box in a prismatic shape with a quadrangular base, and a lid on top, whose shape suggests pyramids placed on top of one another. On one side of the box, there is a small door used to put candles in the box. On the opposite side, slightly above the upper part of the door, there is a circular orifice 4.5 cm in diameter. The other sides have, at the same level as this orifice, circular inlaid work with the same dimensions as the orifice. All of the sides of the box have geometrical shapes at the level of the door, in inlaid wood, which suggest false doors.

The experiments were performed by placing a lit candle inside the box and by removing the lid in order to keep the candle lit. When the assemblage was placed in a dark room, the orifice allowed the candle to illuminate an object, for example, a page from a book, which had to be placed at a distance from the orifice that would make it difficult to read the page. So that the conditions of illumination of this page would be identical to these conditions when the same page was re-located at a distance twice as far as the first, it was necessary to place a group of 4 candles in the box. Thus, the teacher of experimental physics could show that the intensity of the illumination of a target produced by a source of light diminished as the target was moved away from the source, in inverse proportion to the square of the distance at which it was placed.