From the earliest times it was empirically known that a boat could be turned if the oar was put in the sea over the side of the boat. From the thirteenth century also it was empirically known that for this reason it is better to use a rudder over the stern. The reason for the boat turning was not known, although the question was put probably very early. In the seventeenth century such questions surely were posed in scientific treatises, but at that time it was impossible to find a satisfactory solution. Before the eighteenth century it was not possible to solve this problem of hydrodynamics (when the serious mathematical foundations of hydrodynamics were propounded in the works of Daniel Bernoulli, Pierre Bouguer, Leonhard Euler and other eminent scientists).