  As was observed in   Section 5.3,   it had been experimentally established that the osmotic pressure of a solute in small concentrations obeys the gas laws. A natural step from the point of view of the kinetic theory is to assume that the difference between the molecules of a solute distributed through the liquid in which it is dissolved and Brownian particles all of like size suspended in a liquid is simply one of scale. Einstein (1905, 1906,1907) was the first to stress this point and to give a detailed account of Brownian motion as a thermal agitation. Perrin's initial work on the density distribution of Brownian particles seems to have been carried out in ignorance of Einstein's paper. But it was soon brought to his attention and influenced his subsequent work with full acknowledgment given to Einstein.