(Top) Shadowgraph visualization of rising and falling plumes at Ra=6.8 × 108, Pr=596 (dipropylene glycol) in a Γ=1 cell (from Ref. ). (Bottom) Small thermochromic liquid-crystal spheres are seeded in the convecting fluid. Their Bragg-scattered light changes color from red to blue in a narrow temperature range. Streak pictures of the spheres with a long exposure time show the temperature and velocity fields simultaneously. Cooler regions appear brown and warmer regions appear green and blue. This image was taken near the top surface at Ra=2.6 × 109 and Pr=5.4 (water). The view shows an area of 6.5 cm by 4 cm. Near the middle top one sees a brownish (cold) plume detaching from the boundary layer, extending down and to the left into the fluid, and forming a mushroom head consisting of two swirls (from Ref. ).