Lanchester, F.W., "Aerodynamics", 1907, quoted in Anderson, J.D., "Fundamentals of Aerodynamics", Fig. 5.42, p. 366, 2nd Edition, McGraw-Hill, 1991.

In Lanchester's " Aerodynamics", we find the first mention of vortices that trail downstream of the wing tips. The essence of the horseshoe vortex concept originated with Lanchester. ( courtesy Anderson, J. D. " Fundamentals of Aerodynamics " )