At 88, historian David Levering Lewis, a biographer of W.E.B. DuBois, has filled in gaps in his knowledge of his own family line, and he takes readers along on the journey.

The 1800s saw the Pound Sterling to US Dollar (GBPUSD) exchange rate by and large maintain a rate of around $5 to every £1 with the notable deviations from the rate seen to be aligned with ...