from The Century Dictionary and Cyclopedia
- n. A rotational motion of a fluid in which there is circulation about certain vortex-filaments, and no circulation except about them.
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But in 1858 the equations of motion of an incompressible frictionless fluid were first successfully solved by Helmholtz, and among other things he proved that, though vortex-motion could not be originated in such a fluid, yet supposing it once to exist, it would exist to all eternity and could not be diminished by any mechanical action whatever.
Once admit even the most infinitesimal amount of friction, while retaining the conception of vortex-motion in a universal fluid, and the whole case is so far altered that the material atom can no longer be regarded as absolutely indestructible, but only as indefinitely enduring.
The india-rubber has then what is called vortex-motion.
In these cases, and in others as we commonly find it, vortex-motion owes its origin to friction and is after a while brought to an end by friction.
"To account for such elasticity," says Professor Clifford (whose exposition of the subject is still more lucid than that of our authors), "it has to be supposed that even where there are no material molecules the universal fluid is full of vortex-motion, but that the vortices are smaller and more closely packed than those of [ordinary] matter, forming altogether a more finely grained structure.
The reader first needs to know what vortex-motion is; and this has been so beautifully explained by Professor Clifford, that I quote his description entire: "Imagine a ring of india-rubber, made by joining together the ends of a cylindrical piece (like a lead-pencil before it is cut), to be put upon a round stick which it will just fit with a little stretching.