A new method for the measurement of surface and interfacial tensions is suggested. The two phases to be investigated are placed in a closed container which is rotated at a known speed about a horizontal axis. Under the influence of the forces of rotation and of surface tension the lighter phase will take the equilibrium shape of an elongated bubble along the axis of rotation. If the length of the bubble is made large compared to the radius, the shape of the bubble can be closely approximated by a circular cylinder with hemispherical ends. For the case of a long bubble expressions are derived for the surface tension as a function of the bubble dimensions and for the shape of the bubble end.