Page "Curl (mathematics)" Paragraph 46

We might not see any rotation initially, but if we closely look at the right, we see a larger field at, say, x = 4 than at x = 3.

Intuitively, if we placed a small paddle wheel there, the larger " current " on its right side would cause the paddlewheel to rotate clockwise, which corresponds to a curl in the negative z direction.

By contrast, if we look at a point on the left and placed a small paddle wheel there, the larger " current " on its left side would cause the paddlewheel to rotate counterclockwise, which corresponds to a curl in the positive z direction.

Let's check out our guess by doing the math: