Operation Earthworm By: Joe Archibald

Operation Haystack By: Frank Herbert

Operation Lorelie By: William P. Salton

Operation R.S.V.P. By: H. Beam Piper

Optical Projection Part 1: Projection of Lantern Slides By: Russell S. Wright

Organic Syntheses By: James Bryant Conant

Origin and Nature of Emotions By: George W. (Washington) Crile

Origin of Species By: Thomas Henry Huxley

Other Worlds Their Nature, Possibilities and Habitability in the Light of the Latest Discoveries By: Garrett Putman Serviss

Our Bird Comrades By: Leander S. Keyser

Our Common Insects A Popular Account of the Insects of Our Fields, Forests, Gardens and Houses By: Alpheus S. Packard

Our Friend the Dog By: Maurice Maeterlinck

Out Around Rigel By: Robert H. Wilson

Out Like a Light By: Randall Garrett

Out of This World Convention By: Forrest J. Ackerman

Outlines of a Mechanical Theory of Storms Containing the True Law of Lunar Influence By: Thomas Bassnett

Outlines of Dairy Bacteriology, 8th edition A Concise Manual for the Use of Students in Dairying By: H. L. (Harry Luman) Russell

Outlines of Greek and Roman Medicine By: James Elliott

Outlines of Lessons in Botany, Part I; from Seed to Leaf By: Jane H. Newell

Pagan Passions By: Laurence M. Janifer

Pandemic By: Jesse F. Bone

Papers on Health By: John Kirk

Personal Experience of a Physician By: John Ellis

Personal Narrative of Travels to the Equinoctial Regions of America, During the Year 1799-1804 — Volume 1 By: Alexander von Humboldt

Personal Recollections, from Early Life to Old Age, of Mary Somerville By: Mary Somerville

Peter Cooper The Riverside Biographical Series, Number 4 By: Rossiter W. (Rossiter Worthington) Raymond

Pharaoh's Broker Being the Very Remarkable Experiences in Another World of Isidor Werner By: Ellsworth Douglass

Philosophical Transactions of the Royal Society - Vol 1 - 1666 Giving some Accompt of the present Undertakings, Studies, and Labours of the Ingenious in many considerable parts of the World By: Various

Philosophy of Osteopathy By: A. T. (Andrew Taylor) Still

Physics and Politics, or, Thoughts on the application of the principles of "natural selection" and "inheritance" to political society By: Walter Bagehot

Pioneer Surgery in Kentucky A Sketch By: David Wendel Yandell

Pipe of Peace By: James McKimmey