Hudson, W. H. (1894). An introduction to the philosophy of Herbert Spencer: With a biographical sketch. D. Appleton and co..
Chicago-referens (17:e uppl.)Hudson, William Henry. An Introduction to the Philosophy of Herbert Spencer: With a Biographical Sketch. New York: D. Appleton and co., 1894.
MLA-referens (8:e uppl.)Hudson, William Henry. An Introduction to the Philosophy of Herbert Spencer: With a Biographical Sketch. D. Appleton and co., 1894.
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