Tracing history through objects is popular these days. Neil McGregor, the director of the British Museum, did it in 700 best-selling pages, and for the last couple of months, the New-York Historical Society has had an exhibition called “The Civil War in 50 Objects.”

Finding the 50 objects involves something of a scavenger hunt — they are on display in different places at the society, at 170 Central Park West, at West 77th Street. All 50 came from the society’s collection of about 1 million Civil War-era items, “a definitive record of slavery, secession, rebellion and reunion from the time these movements first roiled the city and the nation,” according to the Lincoln scholar Harold Holzer. He made the final decisions on which 50 objects were chosen, and which were not, after members of the museum’s staff had winnowed the possibilities to 75....