Kenneth Schuyler Lynn, a historian of American thought noted for his analytical studies of Mark Twain, Charlie Chaplin and Ernest Hemingway, died on June 24 at Memorial Sloan-Kettering Cancer Center in New York. He was 78 and lived in Washington.

The cause was complications from leukemia, his family said.

Dr. Lynn taught at the Johns Hopkins University from 1969 until his retirement as Arthur O. Lovejoy Professor of History emeritus in 1989. He was previously a professor of English and chairman of an American civilization program at Harvard.

Working as a biographer, essayist, literary critic and editor, he blended his interests in history and American letters. His searching studies of Hemingway and Chaplin, among others, were widely reviewed and generally acclaimed.

"Hemingway" (Simon & Schuster, 1987) delved into that author's boyhood and the influence of his mother, Grace, who insisted on treating him and his older sister as twins of the same sex. The resulting confusion in sexual identity lingered for the rest of Hemingway's life, Dr. Lynn argued.