What did Hermann von Helmholtz discover about vortices in an ideal fluid?

In his 1858 paper, "On the Integrals of Hydrodynamic Equations to Which Vortex Motions Conform," Hermann von Helmholtz demonstrated that vortices within an ideal fluid possess remarkable stability.1

His mathematical analysis revealed that these vortex structures could collide elastically, intertwine into complex, knotlike configurations, and undergo various tensions and compressions while maintaining their individual identities. This work was highly influential; it later led William Thomson (Lord Kelvin) to propose that such vortices, if formed within the ether, could serve as the fundamental building blocks or "primeval atoms" of solid matter.1