1867 P. G. Tait tr. Helmholtz in 4th Ser. 33 510 These vortex-rings travel on,..and are widened or contracted by other vortex-rings.
1878 W. K. Clifford iii. 205 Suppose that in a mass of fluid there is a single vortex ring of any form (i.e. a vortex-filament returning into itself).