Arthur Eddington opens his 1928 Gifford Lectures with two tables: the solid one he leans his elbows on, and the one physics describes — mostly empty space, its apparent solidity an effect of forces between sparse particles. From there he walks through relativity, quantum theory, and entropy’s arrow of time, arguing that the observing mind is what turns those equations into a world that feels real. Free on Project Gutenberg in EPUB, Kindle, or plain text.