Instead, it rotates around the axis that the light is propagating along.

The light can propagate only up, out of the crystal, or down, where it strikes another cuticle layer that acts as a Bragg reflector.

In addition to propagating through a vacuum, light may also propagate through many types of matter, denoted as the medium.

Exceptions arise when the light propagates either along or orthogonal to the optical axis.

The implications were undeniable: the idea of ether as a fixed reference frame through which light must propagate was coming undone.

The "ray" in geometric optics is an abstraction, or "instrument", which can be used to approximately model how light will propagate.

This form of aether was viewed as the medium through which light could propagate.

The media the light must propagate through can effect the image quality.

Explaining his results by interference of the waves emanating from the two different slits, he deduced that light must propagate as waves.

The optical axis is an imaginary line that defines the path along which light propagates through the system.