Transverse pressure and secondary flow

In the steady state, the x component of the momentum transport equation (3.3.1) yields 

The transverse pressure difference was directly demonstrated by Pieranski and Guyon by measuring the liquid level difference in tubes connected to holes facing each other across the width / of the cell. Its dependence on predicted by (3.6.25) was verified (fig. 3.6.9(a)). It vanishes for = 0 and njl. Further, it was confirmed that it changes sign when the flow is reversed or when the field is rotated so that (j becomes — 

For wide cells L, the length of the cell measured along y) it was found by observing the motion of dust particles that the flow lines are not along y (in other words, the assumption that = 0 is no longer valid). In 

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