It is an instrument for the study of elastic impact which also exists in a modern version as a teaching aid and scientific toy. It consists of seven ivory balls (diameter 3.8 cm) suspended from two horizontal, parallel bars, a rectangular frame supported by a column of adjustable height (minimum 62 cm, maximum 120 cm) on a wide, rectangular base 33 x 28 cm all of wood.
Each ball hangs from a string that is doubled with the ends tied to the two bars of the frame by means of screw hooks which are fixed on one bar and adjustable in height and distance along the bar to allow the balls to be perfectly aligned along the bar and with their centres at the same height and in contact with each other.
An impulse imparted to the first ball by removing it from its rest position and allowing it to fall is transmitted from one ball to another up to the last with no appreciable movement of those in the middle. In fact, each of the intermediate balls, being elastic, is slightly deformed and, on reacquiring its original form, shifts imperceptibly, transmitting the impulse to the next one. If the first ball is raised and dropped, the intermediate ones remain immobile and the oscillation is completed on the other side by the last ball; if the first two are raised, the last two will complete the oscillation.