A layer of rock that is sufficiently thick, areally extensive, and has a distinctly higher velocity than the rocks immediately above it such that it can transmit a head wave, or a wave transmitted at [..]

1769, as a type of telescope, agent noun from refract.

A type of telescope that uses a transparent convex lens to gather light and bend it to a focal point.

A telescope, also known as a refracting telescope, that uses a transparent lens to gather light and bend it to a focus.

A type of telescope, also known as a refracting telescope, that uses a transparent convex lens to gather the light and bend it to a focal point.

A telescope that gathers light with a lens. The original design showed dramatic rainbows, or “false color,” around stars and planets. Most modern refractors are achromatic, meaning “free of false color,” but this design still shows thin violet fringes around the brightest objects. The finest refractors produced today are apochromatic, meaning “beyo [..]

 - A device used to re-direct the luminous flux from a light source by the process of refraction.

A transparent material, such as a lens or a prism, that bends or refracts light

Controlling light output by means of refraction (lens).

An optic that achieves control of light by means of refraction (using lenses).   S

Telescope using a glass lens to gather light.

A type of telescope that uses a transparent convex lens to gather light and bend it to a focal point.

A card that has chrome reflective devices. These cards often come with a thin removable protective layer. The card loses some value if this plastic layer is removed.