The Prime Radiant is a physical object, often described as a small black cube (small enough to be placed on a table and not take up more space than a standard desk trinket), that encases the mathematical equations that represent the science of psychohistory and its predictions. When activated, the Prime Radiant has the ability to dim the lights of the room in which it is activated, and project the equations on a wall or into the air (not clear). The projection is described as being two-dimensional. Any section of the very elaborate and long equations can me magnified, manipulated, revised, etc...

Initially there were only two Prime Radiants, and they were constructed by Hari Seldon's staff in his later years. One was owned by Seldon himself, the other belonged to Yugo Amaryl. At least one of the Prime Radiants was passed down to Wanda Seldon, and eventually to the leadership of the Second Foundation.

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