1. G. Barr,A Monograph of Viscometry(Oxford University Press, London, 1931), Chap. 2.
2. A. Thom, (British) Aeronautical Research Council, Reports and Memoranda No. 1475 (1932).
3. The pressure difference referred to here is the total difference, i.e., twice the difference between the hemisphere at infinity and the midsection of the tube.
4. The quantity 12QΔP represents the work done on the fluid by surface forces at the boundary of the region. The first equality in Eq. (2) follows from the fact that inertial effects are being neglected, i.e., the rate of increase of kinetic energy is negligible in comparison with the dissipation rate.