Reporter Jacob Riis’s vivid descriptions of poverty in 19th-century New York City horrified a generally complacent public. His book How the Other Half Lives combined his writing with his own photographs to paint a picture so vivid that the public could not escape the certainty of poverty’s desperate existence. The third of fifteen children himself, Riis wrote so effectively because he had lived in that world of terrible despair.

                 Shortly after the release of his book, he received a card from a young man just beginning his political career. The note read simply, “I have read your book, and I…