I didn't want to overload the last topic, "The Meaning of Curl in Electrodynamics", but I have a question so I'll do it as a new thread.

I'm studying The Feynman Lectures on Physics - Vol 2, Sections 3-5 and 3-6: "The Circulation of a vector field" and "The circulation around a square:Stokes' Theorem". I've include a scan of these two sections at http://home.comcast.net/~perion_666/stuff/feynman1.jpg [Broken] and http://home.comcast.net/~perion_666/stuff/feynman2.jpg [Broken] .

In the second section, after eq. 3.33, Feynman says:

My question is - what is "the next approximation" he's referring to. I don't see where any higher order terms like (delta y)^2 terms would come from in this analysis.

Ok, yes - I see it. I wasn't thinking about power series approximation. I guess he had to use that since he used a generalized form for the vector function C(x,y) , so C could be about anything. Thanks.