This macroscopic approach is indispensable to the application of physics to much of modern technology. Thermodynamics, for example, a bmnch of physics developed during the 19th century, deals with the elucidatìon and measurement of properties of a system as a whole and remains useful in other fields of physics; it also forms the basis of much of chemical and mechanical engineering. Such propenies as the temperature, pressure, and volume
0f a gas have no meaning for an individual atom or molecule; these thermodynamic concepts can only be applied directly to a very large system of such particles. A bridge exists, however, between the microscopic and macroscopic approach; another branch of physics, known as statistical mechanics,
indicates how pressure and temperature can be related t0 the motion of atoms and molecules on a
statistical basis,
Physics emerged as a separate science only in thc carly l9th century; until that time a physicist