One evening, when Mr. Hall, astronomer, was working in the Naval
Observatory, Washington, on the great equatorial telescope, he was
startled to have his sanctum invaded by the gaunt, extenuated figure of
the President. He was made welcome, of course, and the varied mechanism
explained to him. As the crowning "treat," he was given a peer through
the celebrated instrument. It was leveled at the moon, or, rather,
arranged to have that orb in its focus at the time. The visitor was
appalled, as well as wondering at the view, and slowly withdrew by the
trap-door. But when the astronomer resumed his observations and
calculations he was interrupted by the same sedate and absorbed caller.
He returned, perplexed, as, on glancing up at the moon with unhindered
vision, he saw it in another position to that presented in the
spy-glass.
Mr. Hall made it clear to him that, as the telescope was pointed, not
at the satellite but at its image in a mirror, he saw its reflection
and consequently the reverse of the face we observe. The President went
away with the satisfaction of a man wanting every novelty demonstrated.
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