These experiments were performed with the aim of verifying the validity of an aether theory of magnetic field. The two cylinders are the equivalents of two parallel current-carrying coils. The cylinders produce water vortices which correspond to aether vortices around current-carrying coils.
See also the case when the two cylinders are placed end-on (https://www.youtube.com/watch?v=RNnXV...). This corresponds to the situation in which the magnetic poles of the current-carrying coils face one another.