APA (7th ed.) Citation

Hill, J. L. (2011). Revisiting the Earth. Project Gutenberg.

Chicago Style (17th ed.) Citation

Hill, James Langdon. Revisiting the Earth. Project Gutenberg, 2011.

MLA (9th ed.) Citation

Hill, James Langdon. Revisiting the Earth. Project Gutenberg, 2011.

Warning: These citations may not always be 100% accurate.