In the nth century it became the seat of the Eppenstein family, who frequently bore the title of counts of Gorizia; and in the beginning of the 12th century the countship passed from them to the Lurngau family which continued to exist till the year 1500, and acquired possessions in Tirol, Carinthia, Friuli and Styria.
Reference may also be made to the treatise of Czapski-Eppenstein, pp. 155-161.
These constants are determined by the data of the system (radii, thicknesses, distances, indices, &c., of the lenses); therefore their dependence on the refractive index, and consequently on the colour, are calculable (the formulae are given in Czapski-Eppenstein, G'rundziige der Theorie der optischen Instrumente (1903, p. 166).
In practice it is more advantageous (after Abbe) to determine the chromatic aberration (for instance, that of the distance of intersection) for a fixed position of the object, and express it by a sum in which each component contains the amount due to each refracting surface (see Czapski-Eppenstein, op. cit.
Eppenstein, was published at Leipzig in 1903 with the title, Grundziige der Theorie der optischen Instrumente nach Abbe, and in vol.