A University of Pittsburgh historian has discovered one of the strangest and most compelling documents ever related to the 18th-century slave trade - and it has a Salem connection so strong that experts at the Peabody Essex Museum are buzzing.

The petition was uncovered by Marcus Rediker, 55, while researching his fifth book, "The Slave Ship: A Human History." It is a bloodcurdling satire, until now lost to history. Written by Scottish doctor, radical, Encyclopaedia Britannica contributor and early hot air balloonist James Tytler, it pretends to be a plea "To the right Honourable the Lords Spiritual and Temporal of Great Britain, in Parliament assembled."