English scientists Robert Hooke and Isaac Newton were the first who observed structural coloration. Thomas Young described its principle a century later and called it wave interference. Young described iridescence as the result of interference between reflections from several surfaces of thin films, combined with refraction as light enters and leaves such films. The geometry then determines that at certain angles, the light reflected from both surfaces adds (interferes constructively), while at other angles, the light subtracts. As a result, different colors appear at different angles.