Ernst Mach (1838 - 1916) observed that some mental experiences are the same even though they are stimulated by a wide range of sensory events. Example is the experiencing of geometric forms/space forms and melodies or time forms. Mach proposed a brand of positivism based on the phenomenological experiences of scientists. Because scientists, or anyone else, never experience the physical world directly, the scientist's job is to precisely describe the relationships among mental phenomena, and to do so without the aid of metaphysical speculation.