Photo: Bobby Doherty/New York Magazine

The good folks beavering away at their long tables in the magisterial north Rose Main Reading Room on the third floor of the New York Public Library’s main building might be excused for feeling spied upon. “What is that thing?” they’ve been asking the guards over the past several months, pointing up at the eerie, tripod-mounted, radarlike dish mounted on the narrow balcony at the far end of the airy, vaultlike space.

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