# How does Huygens' principle explain refraction?

I am told that one of the merits of Huygens' principle is that it could explain refraction, however, in the argument given in my textbook it seems flawed.

This seems like a totally idealised scenario because if I wait a little bit longer,

(If drawn more accurately, the wave fronts shown in the refraction would line up with the wavelets all the time, I don't believe this would be a problem) with the same reasoning, I can assert that the wavefronts are travelling in an entirely different direction. Is this really the correct justification for refraction given with Huygen's theory?

• consider time evolution. The wavefronts you should join are like a picture at a given time. You are joining wavefronts from secondary emitters which do not correspond to a given $t=t_0.$ So for example, join the first wave fronts that each of the secondary emitters have produced. Then join the second ones and so on. It would look like the book's. – Nelson Vanegas A. May 4 '20 at 20:02
• This is probably a homework problem? – user262759 May 4 '20 at 23:50