  We report an experimental investigation of pair dispersions in turbulent
thermal convection with initial separation r0 ranging from sub-Kolmogorov scale
to scales in the inertial range. In the dissipative range of scales we observed
for the first time in experiment the exponential growth of the separation
between a pair of particles predicted by Batchelor and obtained a Batchelor
constant 0.23\pm0.07. For large r0, it is found that, for almost all time
range, both the mean-square separation and distance neighbor function exhibit
the forms predicted by Batchelor, whereas the two quantities agree with
Richardson's predictions for small r0. Moreover, the measured value of the
Richardson constant g = 0.10 \pm 0.07, which is smaller than those found in
other turbulence systems. We also demonstrate the crossover of the mean-square
separation from the exponential to the Batchelor regimes in both temporal and
spatial scales.
