Both historical treatment and critical analysis, this work by a noted physicist takes a fascinating look at a fundamental of physics, tracing its development from ancient to modern times. Kepler's initiation of scientific conceptualization, Newton's definition, post-Newtonian reinterpretation — contrasting concepts of Leibniz, Boscovich, Kant with those of Mach, Kirchhoff, Hertz. "An excellent presentation." — Science. 1962 edition.