In 1844 James Johnson MD, Physician to the Late King, published *A Tour in Ireland; with Meditations and Reflections*. During his tour he had travelled by horse-drawn fly-boat along the Grand Canal from Dublin. On the Long Level (15 lock-free miles) he noted that:
"Having reached the highest level of the great table-land, we traversed a space of fifteen miles without a lock; and here a curious phenomenon, illustrating the incompressibility of water, arrested our attention. About every twenty or thirty minutes, the horses are obliged to stop for five or six minutes, to take breath, the cause of which was this: --- The velocity of the boat impelled the water with such force that it gradually rose so as to approach the summits of the banks, when it began to recoil, so as actually to form a back-water or stream, when the horses were unable to make head, and therefore stopped until the equilibrium of the canal was restored." I have not heard of that phenomenon before. Has anyone else come across it? bjg
