Henry George (2014). “A Perplexed Philosopher: Being an Examination of Mr. Herbert Spencer's Various Utterances on the Land Question, with Some Incidental Reference to His Synthetic Philosophy”, p.6, epubli
Louis Freeland Post, Henry George (1899). “The Single Tax: An Explanation, with Colored Charts and Illustrated Notes of the Land, Labor, and Fiscal Reform Advocated by Henry George”