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Circulation of a Vector

When a closed path C is defined in a vector field F as shown Figurę 1.6 we may define the circulation T of F around the contour C

It is elear that the circulation depends upon the shapc and position of the contour in the field, and upon the direction in which it is traversed in the performance of the linę

integral. Thus it is necessary to define a positive direction for the contour. This has been

done in Figurę 1.6 by means of the arrows shown. Again, as with the definition of the positive direction for a surface, the positive direction may be arbitrarily chosen, but in the context of Stokes' theorem discussed below, a restriction applies.