Heat and Thermodynamics

4.13 Evidences of Molecular Motion

In the earlier part of this chapter we have developed the kinetic concept of matter on the basis of classical mechanics and deduced certain consequences which agree with observed facts. Untill 1908, no direct proof of the perpetual motion of molecules was available to give the kinetic theory a legitimate foundation.

In the year 1827, an English botanist Brown observed that fine colloidal suspensions in water seen under microscope were moving constantly in different directions in erratic manner apparently without any rhyme and reason. The sizes of these particles were thousands of times larger than the size of molecules of the liquid medium. On the basis of the kinetic theory, Brown ventured the assumption that ...