of a vector field A, the vector characteristic of a “rotating component” of field A. The curl is represented by the symbol rot A. It can be interpreted in the following manner: Let A be the velocity field of a fluid flow. At a given point of the flow we place a small wheel with blades and orient its axis in the direction of rot A at that point. Then the angular velocity of the wheel’s rotation from the action of the current will be maximum, and its value will equal (| rot A |)/2. If the field A has the coordinates P(x, y, z), Q(x, y, z), and R(x, y, z), then the curl has the coordinates
E. G. POZNIAK