""Displacement Interferometry By The Aid Of The Achromatic Fringes, Part 4"" is a scientific book authored by Carl Barus, which was first published in 1919. The book focuses on the concept of displacement interferometry, a technique used to measure small displacements or changes in length, which is achieved by observing the interference fringes produced by a light beam that has passed through a pair of closely spaced mirrors. The book is the fourth...