# Velocity of light sentence example

It is there shown that every substance, transparent to light, has a definite refractive index, which is the ratio of the

**velocity of light**in vacuo to its velocity in the medium to which the refractive index refers.The second method is in principle extremely simple, consisting merely in multiplying the observed

**velocity of light**by the time which it takes light to travel from the sun to the earth.The

**velocity of light**(q.v.) has been measured with all the precision necessary for the purpose.Let E be the effective elasticity of the aether; then E = pc t, where p is its density, and c the

**velocity of light**which is 3 X 10 10 cm./sec. If = A cos" (t - x/c) is the linear vibration, the stress is E dE/dx; and the total energy, which is twice the kinetic energy Zp(d/dt) 2 dx, is 2pn2A2 per cm., which is thus equal to 1.8 ergs as above.Bradley recognized the fact that the experimental determination of the aberration constant gave the ratio of the velocities of light and of the earth; hence, if the velocity of the earth be known, the

**velocity of light**is determined.AdvertisementIf N be the frequency of a homogeneous vibration sent out by a molecule at rest, the apparent frequency will be N (1 v/ V), where V is the

**velocity of light**and v is the velocity of the line of sight, taken as positive if the distance from the observer increases.Hertzian waves have the

**velocity of light**itself.By the use of a revolving mirror similar to that used by Sir Charles Wheatstone for measuring the rapidity of electric currents, he was enabled in 1850 to demonstrate the greater

**velocity of light**in air than in water, and to establish that the**velocity of light**in different media is inversely as the refractive indices of the media.With Wheatstone's revolving mirror he in 1862 determined the absolute

**velocity of light**to be 298,000 kilometres (about 185,000 m.) a second, or 10,000 kilom.Abraham, showed it to be very close to the best determinations of the

**velocity of light**(see Physical Units).AdvertisementTo him is also due the discovery of the power of rotatory polarization exhibited by quartz, and last of all, among his many contributions to the support of the undulatory hypothesis, comes the experimentum crucis which he proposed to carry out for comparing directly the

**velocity of light**in air and in water or glass.Again, since the constant of aberration defines the ratio between the

**velocity of light**and the earth's orbital speed, the span of the terrestrial circuit, in other words, the distance of the sun, is immediately deducible from known values of the first two quantities.Nevertheless, it is still assumed to occur, and its purely conjectural magnitude determines what we call the '

**velocity of light**' .Availing himself of the admirable generalized co-ordinate system of Lagrange, Maxwell showed how to reduce all electric and magnetic phenomena to stresses and motions of a material medium, and, as one preliminary, but excessively severe, test of the truth of his theory, he pointed out that (if the electromagnetic medium be that which is required for the explanation of the phenomena of light) the

**velocity of light**in vacuo should xvii.In addition to the doubt thrown on this result by the discrepancy between various determinations of the constant of aberration, it is sometimes doubted whether the latter constant necessarily expresses with entire precision the ratio of the velocity of the earth to the

**velocity of light**.AdvertisementHe early directed his researches to the

**velocity of light**and while in Cleveland invented his interferometer (see 14.693), which enabled him to measure distances by means of the length of light-waves.The latter force is, by Maxwell's hypothesis or by the dynamical theory of an aether pervaded by electrons, the same as that which strair s the aether, and may be called the aethereal force; it thereby produces an aethereal electric displacement, say (f,g,h), according to the relation (f,g,h) = (41 r c 2) - 1(P',Q', RI), in which c is a constant belonging to the aether, which turns out to be the

**velocity of light**.