  Mach’s views on atomism are most clearly presented in an exchange with Planck. In 1909 Planck wrote an essay “The Unity of the Physical World-Picture”, which contained a severe criticism of Mach’s philosophy. Mach replied in 1910, with “The Guiding Principles of My Scientific Theory of Knowledge and Its Reception by My Contemporaries.” Planck responded in 1910 with “On Mach’s Theory of Physical Knowledge: A Reply.”