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the difference between (77) and (78) is reduced to a variation of the phases, namely this will be determined for an arbitrary molecule by

${\frac {{\mathfrak {p}}_{x}}{V^{2}}}\xi +{\frac {{\mathfrak {p}}_{y}}{V^{2}}}\eta +{\frac {{\mathfrak {p}}_{z}}{V^{2}}}\zeta$

consequently it is not equal for the various molecules.

It is now to be noticed, that the molecules of a light source, e.g. a flame, must be considered as totally independent from one another, so that, as it is ordinarily expressed, the rays emanated by two of these particles cannot mutually interfere. From that if follows, that arbitrary variations in the phases of the single molecules cannot have any influence on the observable phenomena. The stationary light source with motions (78) will give nothing other than a stationary source (also at rest) with motions (77), and thus we may claim:

If we set a light source into translation, without changing anything of the oscillations of their ions, then the observable phenomena in bodies rigidly connected with them, remain as they were.

§ 67. Numerous experiments have proven, that when using terrestrial light sources, the phenomena are indeed independent of the orientation of the devices with respect to the direction of Earth's motion. Here, the observations of Respighi,^[1] Hoek,^[2] Ketteler^[3] and Mascart^[4] on refraction do belong, as well as the experiments of the three last mentioned physicists on interference phenomena.^[5] We are indebted to Ketteler for an investigation on the inner reflection and the refraction at calcite prisms.^[6] and

1. Respighi. Memor. di Bologna (2), II, p. 279. (Cited in Ketteler. Astronomische Undulationstheorie, p. 66).
2. Hoek. Astr. Nachr., Bd. 73, p. 193.
3. Ketteler. Astr. Und.-Theorie, p. 66, 1873; Pogg. Ann., Bd. 144, p. 370,1872.
4. Mascart. Ann. de l'ecole normale, 2e sér., T. 3, p. 376, 1874.
5. Hoek. Arch. neerl., T. 3, p. 180, 1868. Ketteler. Astr. Und.-Theorie, p. 67; Pogg. Ann., Bd. 144, p. 372. Mascart. L. c., pp. 390—416.
6. Ketteler. Astr. Und.-Theorie, pp. 158 and 166; Pogg. Ann., Bd. 147, pp. 410 and 419, 1872.