(Refer Slide Time: 49:30)
Again only for closed curves or terminate at a boundary surface, for example, if we look at the smoke rings. In case of a smoke rings the vortex lines they from close curves on the other hand in case of while pole the vortex lines, the terminate at a boundary in the fluid. If we look at the hurricane another example is that in case of hurricane the eye of hurricane we know, that it is always makes a circular motion.