An induction-loop would be installed in the gallery and receivers freely available. The effective field of this loop would be curtailed well short of the extremities of the gallery. Thus a visitor equipped with receiver, wandering through, could expect to find very many positions where no signal is received, and many where one is received. This signal would be without variety, the receiver being capable of only two states, quiescent and active, depending on the visitor’s location within or out of the loop.
A visitor, suitably equipped with receiver and locomotor inclination, would find that in moving into the gallery, after several steps with nothing issuing from the instrument, a point is reached when a signal is received. He would find that further progress in any direction (other than reverse) brought about no further change in the receiver’s state and a signal of constant pitch and intensity is heard. After several further steps this signal would abruptly cease. After some minutes the visitor might be prepared to assign a ‘form’ to an area of the gallery and a patient and methodical visitor might endeavour to offer some ‘dimensions’ of this area.The loop itself, consisting of a fine wire, would either be fixed to the ceiling or located under a carpet, provided it went wall-to-wall, either way one would try to conceal it.