Second normal stress difference of a Boger fluid

Measurement of the second normal stress difference for a highly elastic, constant viscosity 'Boger fluid' is reported. Two very different experimental techniques have been used: (1) measurement of the height of the free surface in rod-climbing flow; (2) measurement of the pressure distribution in cone-and-plate shearing flow. The second normal stress difference is at least 30 times smaller in magnitude than the first normal stress difference, and opposite in sign. The results should prove useful in distinguishing between the various constitutive equations proposed for Boger fluids.