Gibbs was an active
abolitionist and he played an important role in the
Amistad trials of 1839–40. By visiting the African passengers in jail and showing them piles of pennies, he was able to learn to count to ten in the language spoken by most of them, which was determined to be
Mende. Gibbs then strolled around the harbors in New Haven and
New York City, counting aloud from one to ten in the words he had learned from the Africans. In this way he eventually met two British sailors,
James Covey (a former slave) and Charles Pratt, who recognized the words and could serve as interpreters. The sailors also taught some Mende to Gibbs and to fellow Yale professor George E. Day, enabling them to converse with at least 20 of the captives. Gibbs and Day testified as expert witnesses during the trial, establishing that the claim by the owners of the
Amistad ship that the black passengers were slaves born in
Cuba was false. Gibbs later compiled and published vocabularies on Mende and other
West African languages. ==Personal life==