Thanks for this post, that I only read today. Last week was very busy, and I didn't have much time…

I have a few remarks. I hope that you don’t mind.

First, it was really nice to see that you mentioned the name of Priestley. However, it would be fair to also mention those of Bernoulli, Franklin, Robison and Cavendish. Their individual work that gave rise to what is known as the Coulomb law today.

By the way, whereas you discussed the magnitude of the Coulomb force very well, I would be more specific about its direction. When we estimate the force generated by an electric charge q₁ on an electric charge q₂, this force acts along the line drawn between the two charges (your second item). However, it is important to specify that its direction is always from q₁ to q₂. Then, the product of the two charges may flip this direction if the two charges have a different sign.

Finally, note that you may have given me some ideas for my future exam on electromagnetism with the copy machine story (which I didn't know) ;) Thanks!

Cheers!