Figure 3-15

Liquid in a rectangular channel with differing contact angles..

The contact angle on the red wall is 40 degrees, on the brown wall it is 70 degrees, and on the bottom it is 30 degrees. Therefore the red wall exerts a higher capillary force than the brown wall, so the liquid advances faster along the red wall. The contact angle on the red wall is low enough for a Concus-Finn filament to form, but not on the brown wall, so the red wall filament could get arbitrarily far in front of the brown wall filament.