Physics

Free to read here, from Project Gutenberg.

The Complete Works in Philosophy, Politics and Morals of the late Dr. Benjamin Franklin, Vol. 3 [of 3]

Benjamin Franklin

The Complete Works in Philosophy, Politics and Morals of the late Dr. Benjamin Franklin, Vol. 2 [of 3]

Benjamin Franklin

Physics

Willis E. Tower and others

Fragments of Science: A Series of Detached Essays, Addresses, and Reviews. V. 1-2

John Tyndall

The Complete Works in Philosophy, Politics and Morals of the late Dr. Benjamin Franklin, Vol. 1 [of 3]

Benjamin Franklin

The Poetry of Science; or, Studies of the Physical Phenomena of Nature

Robert Hunt

Philosophy

Bertrand Russell, also an audiobook

Popular scientific lectures

Ernst Mach

Preliminary Discourse on the Study of Natural Philosophy

John F. W. Herschel

The New Physics and Its Evolution

Lucien Poincaré, also an audiobook

Conversations on Natural Philosophy, in which the Elements of that Science are Familiarly Explained

Mrs. Marcet and Thomas P. Jones

Science for the School and Family, Part I. Natural Philosophy

Worthington Hooker

The nature of the physical world

Arthur Stanley Eddington, Sir

On the various forces of nature and their relations to each other

Michael Faraday

Grounds of Natural Philosophy: Divided into Thirteen Parts

Margaret Cavendish Newcastle, Duchess of

New and Original Theories of the Great Physical Forces

Henry Raymond Rogers

A Course of Mechanical, Magnetical, Optical, Hydrostatical and Pneumatical Experiments

William Whiston and Francis Hauksbee

Elémens de la philosophie de Neuton: Mis à la portée de tout le monde

Voltaire

French

First Lessons in Natural Philosophy for Beginners

Joseph C. Martindale

Lehrbuch der Physik zum Schulgebrauche.

Wilhelm Winter

German

The analysis of matter

Bertrand Russell

Five of Maxwell's Papers

James Clerk Maxwell

Ancient and Modern Physics

Thomas Edgar Willson

The logic of modern physics

P. W. Bridgman

James Clerk Maxwell and Modern Physics

Richard Glazebrook

Natuurkunde in de Huiskamer: ongeveer 100 proeven met huishoudelijke voorwerpen.

Tom Tit

Dutch

Warum und Weil. Physikalischer Teil.

Otto Ule

German

Wonders of physical science

E. E. Fournier d'Albe

Archimedes; or, the future of physics

Lancelot Law Whyte

The evolution of mathematical physics

Horace Lamb, Sir

Eight Lectures on Theoretical Physics, Delivered at Columbia University in 1909

Max Planck

The highest aim of the physicist

Henry Augustus Rowland

Matter, Ether, and Motion: The Factors and Relations of Physical Science

A. E. Dolbear

Moderne Probleme der Physik

Hermann Sieveking

German