Economic historians Robert W. Fogel and Stanley L. Engerman in the 1970s, through their work "Time on the Cross", portrayed slaves as having internalized the Protestant work ethic of their owners. In portraying the more benign version of slavery, they also argue in their 1974 book that the material conditions under which the slaves lived and worked compared favorably to those of free workers in the agriculture and industry of the time. (This was also an argument of Southerners during the 19th century.)