In 1961 Hendricks published The Edison Motion Picture Myth in which he showed that it was not Thomas Alva Edison who should be attributed with the invention of the first device for cinema screenings, but in fact William Kennedy Laurie Dickson.
Hendricks was the first motion picture specialist to lecture in the Sunday series at the Metropolitan Museum of Art.
He was the first to show motion pictures in the Great Hall at Cooper Union.
At the time of his death, Hendricks was engaged in writing a book about the art of Thomas Cole.
After his death Hendricks bequeathed two major collections to the Archives of American Art: one about Thomas Eakins, the other about film history.