I was reading the Feynman lectures, on the parts that deal with optics, and he explains diffraction in a very interesting way. He imagines a diffraction grating to be made up of a long line of infinitesimal dipole oscillators, all oscillating in phase. What I don't understand is, in which direction are all these oscillators aligned? If you consider the grating as a line of oscillators, are the oscillators aligned such that they oscillate in and out of the paper or such that they oscillate along the line? I have understood thus far in this fashion: that a dipole oscillator is simply a wire along which charges (electrons) move up and down. So then in my case, I thought a diffraction grating would be charges oscillating about infinitesimal wires aligned perpendicular to the plane along which I have assumed the line of oscillators to be on.