The paper describes the apparatus and measurement procedure for tracking lo
ng time trajectories of a single colloidal particle undergoing Brownian mot
ion in water. The bulk motion obeys the Einstein-Stokes formulation, while
sedimented motion is slowed by an additional drag known as the wall-drag ef
fect. The sedimented particle trajectory is long enough to show diffusive m
otion spanning four decades in time. We describe the sample preparation, tr
acking routine, data-acquisition and noise. The experiment shows that Brown
ian motion exhibits a positive dynamic entropy consistent with microscopic
chaos. The theoretical relevance of the experimental results is discussed.
(C) 2001 Published by Elsevier Science B.V.