As the satellite traces
out a 1.5 - hour - long
orbit, a characteristic rise and fall in the difference between the two applied voltages would indicate that one
of the cylinders is falling
slightly faster than the other — and signal a violation
of the equivalence principle.
He knew where to look because two other scientists, John Couch Adams
of Britain and Frenchman Urbain Jean Joseph Le Verrier, had noticed that the planet Uranus was being pulled
slightly out of its normal
orbit, and calculated that the effect was being caused by yet another unknown planet.