“Before I begin the lecture, I wish to apologize for something that is not my responsibility: Physicists and scientists all over the world have been measuring things in different units, and causing an enormous amount of complexity. As a matter of fact, nearly a third of what you have to learn 1 consists of different ways of measuring the same thing, and I apologize for it…

“The physicists do something else when they want to talk about the energy of a single atom, instead of the energy of a gross amount of material. The reason is, of course, that a single atom is such a small thing that to talk about its energy in joules would be inconvenient. But instead of taking a definite unit in the same system (like 10^-20 J), they have unfortunately chosen, arbitrarily, a funny unit called an electronvolt (eV), which is the energy needed to move an electron through a potential difference of one volt, and that turns out to be about 1.6 10^-19 J. I am sorry that we do that, but that’s the way it is for the physicists.”