XXIII. Experiments on the friction between water and air

We have only a few notices on the subject of the friction between air and water, and these few contradict each other. J. B. Venturi states that the air put into motion by a jet of water moves light bodies. G. Magnus opposes this, as he finds that a flame brought near to a vertical jet of water indicates no motion of the surrounding air. The following experiments show, however, that great friction does really take place between water and air, so great as scarcely to differ from total adhesion. But it is very much to be doubted whether Venturi was acquainted with this pure friction between water and air, as he does not say any thing about the constitution of his jets. It must be remembered that Venturi experimented long before Savart, who was the first to distinguish the two parts of a vertical jet of water, the continuous part and the other broken up into drops. The above-mentioned phenomenon can be demonstrated only on the first part, though the discontinuous part of the jet moves the surrounding air too, and with much more energy. But in this case Magnus was quite right when he attributed the motion of the air to other causes.