The engine in the temple

The Museum of Alexandria still stood under Roman rule, its scholars housed and tax-free by the emperor's grace. There Heron the engineer built machines that astonished the age. A hollow brass sphere spun on its pivots when a fire boiled water beneath it, whirling on nothing but the steam that escaped it. He made temple doors that opened when the altar was lit, and a bronze box that gave out holy water when a coin dropped through it. All of it was kept as wonder and toy, marvels for the gods and amusements for the rich. Grain was ground by slaves and by donkeys, and no one thought the spinning sphere was good for anything. A grain merchant of the great harbor stood and watched it turn.

In the timeline recorded here, the merchant asks Heron a question the age never thought to ask. He does not ask how the sphere turns. He asks what it could turn for him, and opens his purse to find out.