Fermat's principle states that light travels between two points in such a way that the total time traveled is a minimum. Since light travels at different speeds through different media, the path of least time may not be a straight line. In particular, light travels a longer distance in the medium in which it has a higher speed. You can find the path followed by the light ray by dragging the point on the boundary between the two media so as to minimize the total time traveled. At this minimum, , as predicted by Snell's law.