APA (7th ed.) Citation

Pickering, E. C. (2011). A Plan for Securing Observations of the Variable Stars. Project Gutenberg.

Chicago Style (17th ed.) Citation

Pickering, Edward C. A Plan for Securing Observations of the Variable Stars. Project Gutenberg, 2011.

MLA (9th ed.) Citation

Pickering, Edward C. A Plan for Securing Observations of the Variable Stars. Project Gutenberg, 2011.

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