An intriguing and educational display structure (1) appears to be spinning
upon itself without any apparent drive mechanism, power supply or bearing. The
structure comprises two concentric hollow spheres (3, 5) spaced apart by
a transparent fluid (6). The outer sphere is totally transparent, immobile
and may rest on a tripod (2) or other type of support. The inner sphere
may be partially transparent or translucent and carries over its surface, a design
such as a map of the world (7). The inner sphere rotates within, and independently
from the first outer one. The internal, that is self-contained drive mechanism
is referenced to either a compass, a light angle detector, or a gravity sensor,
and uses either a conventional electrical motor with its own internal field winding
and communitator, or one made of a rotor comprising a cross-array of electromagnets
(AC, BD) that interact with the earth magnetic field.