Why is the letter "F" used for the curvature 2-form?

Question

Given a differentiable manifold $X$, a vector bundle $E\to X$ and a connection $A$ on $E$. The curvature $2$-form of the connection is a $2$-form with values on the endomorphisms of $E$ defined as $$F(A)=dA + A \wedge A.$$ My question is: Why the letter "F" seems to be the standard choice of symbol for the curvature form?.

At least all the references I am using use have chosen to use this letter.

Answer 1

I suspect this originates in Minkowski's use of it for the electromagnetic tensor in his famous paper on electromagnetism in special relativity, The Fundamental Equations for Electromagnetic Processes in Moving Bodies

In particular, notice his use of $F_{12}$ &c. in this section.

(Why he uses $F$, I don't know.)

Answer 2

One reason is that the pull back of the curvature 2-form via a local section of the principal bundle is called the "gauge field strength" and is denoted by F.

BTW: A gauge field is just the pull back of the connection 1-form via a local section.

Here is a reference

http://empg.maths.ed.ac.uk/Activities/GT/Lect2.pdf