ABSTRACT
The Definition of Mass. Mass is often defined as the quantity of matter in a body, and it is measured by weighing the body. Both definition and fundamental method of measurement, however, are wrongly so stated. How inaccurate the definition is will be seen shortly: measurement by weighing, on the other hand, does not give inaccurate results but is permissible only by virtue of what, from the point of view of the special theory of relativity, is the happy accident that the ' inertial ' mass of a body is equal to. its C gravitational' mass. When we are considering a fundamental modification of the measurement of mass we must take into account only the fundamental definition.
