There is a pillar made of glass (laid horizontally). Light ray (emitted from a light source that is fixed at the left end of the pillar) is passing through this glass (from the left to the right). In front of an observer (at a standstill), one pillar is moving to the right and another pillar is moving to the left at the same speed. To an observer, whether speed of light in the glass is different or not ? (How about, if another light source is fixed at the right end ?)