A prototype viscometer of novel design is described. Experiments using the viscometer with solutions of polybutadiene in decalin were carried out, and measurements were taken of thread tension and filament radius. Using a force‐balance equation, these results were used to evaluate the axial stresses in the filament. The effects of gravity, inertia, aerodynamic drag, and stress history on the elongational viscosity are shown. The results are discussed in the light of previous experimental results and theoretical predictions of the elongational viscosity.