Mercury’s track wandered just a little bit more than the theory predicted.
It was a small number—tiny, really—but the gap between theory and the data was greater than estimates of observational errors could explain, which meant the problem was real.
It took him more than a decade to prepare, but by 1858, he had fitted his telescope with homemade instruments good enough to fix the position of objects within its field of view. He has just missed its first appearance at the edge of the sun.
Working backward from its apparent rate of motion, he estimates the time it crossed the solar limb at almost exactly four o’clock or, to be precise, at pm., plus or minus five seconds.
He would steal time there between patients, just minutes sometimes, sneaking from his office to the dome to look, perhaps to dream, just a little.
The discovery of the asteroids in the belt between Mars and Jupiter led him to wonder: where else might such treasures lurk?
He writes that down, using a piece of charcoal to scratch on a board.
Another patient arrives and, likely with unrecorded frustration, he pulls his eye from his telescope. The spot is still there, moving across the face of the sun.
He had already produced the most accurate theory 16 years earlier, and this time, he expected to do better. But there was still a discrepancy that couldn’t be explained.
But the stakes of the search were just as high in both cases.
Until Mercury’s precession could be accounted for, the anomaly represented a violation of the cosmic order, unthinkable (of course) to all of Newton’s heirs.
During totality, the region closest to the limbs of the sun would suddenly be freed from the brutal glare of the sun, until “at the decisive moment,” Faye wrote, the few minutes of totality “would suffice to explore much of the area designated by M.
Le Verrier.” Faye’s report sparked a wave of preparation.