The change in this quantity between two minerals can be measured using the Becke line test. Phase-contrast imaging relies on the fact that, in the presence of X-rays, this quantity is equal to one minus a delta term on the order of 10 to the negative 5th. This quantity is added to an imaginary extinction coefficient term to model absorption (10[1])in materials. Victor Veselago proposed the existence of “left-handed” materials for (10[1])which this quantity is negative. The square (10[1])of this quantity is equal to the product of relative permittivity and relative permeability. (-5[1])This quantity times the sine (-5[1])of an angle of incidence is (10[1])constant between two media by Snell’s law. (-5[1])For 10 points, (10[1])name (10[1])this quantity that is equal to the ratio of the speed of light (10[1])in a vacuum (10[1])to the speed of light in a medium. ■END■ (10[1])