FRAUNHOFER, Joseph (1787-1826). Bestimmung des Brechungs- und Farbenzerstreuungs-Vermgens verschiedener Glasarten. Extract from: Denkschriften der koeniglichen Academie der Wissenschaften zu München, vol.5 (1817), pp.193-226. Munich: Lentner, 1817.
4o (247 x 208 mm). Half-title, title-page, and 4-page index. 3 engraved plates (2 folding). Later wrappers (spine perishing).
FIRST EDITION of a fundamental paper in astrophysics. Fraunhofer, a skilled optician and designer of precision optical instruments, described in this paper, read before the Bavarian Academy in 1815 his accidental discovery of the absorption lines of the solar spectrum. In 1814, while conducting tests on the dispersion and refractive index for different kinds of optical glass, Fraunhofer "observed the effect of the refracting medium on light, comparing the effect of light from flames with light from the sun, and found that the solar spectrum was crossed with many fine dark lines, a few of which William Hyde Wollaston had observed and reported upon in 1802. [Wollaston had incorrectly interpreted the lines as borders between the colors.] Designating the more distinct lines with capital letters... he mapped many of the 574 lines that he observed between B on the red end and H on the violet end of the spectrum. Sometime later he noted that some of these lines appeared to correspond to the bright doublet of lines in many flame spectra; yet he noted further that while the pattern observed for the sun and planets [being reflected sunlight] appeared identical, the patterns for the sun, Sirius, and other bright stars differed from one another". He concluded that the lines originated in the nature of the light source. "These observations stimulated considerable interest for the next half-century among natural philosophers, whose speculations culminated in the classical explanation of absorption and emission spectra made by Kirchoff and Bunsen in 1859" (DSB). The dark lines, whose exact explanation has never been explained, are still known as Fraunhofer lines. Their discoverer continued to explore and map them during the following years; using a grating device of this own invention he eventually was able to determine the wavelengths of specific colors of light and to make highly precise measurements of dispersion (see below). Although his research was conducted with the purely practical aim of producing the finest possible optical instruments, Fraunhofer's achievements "justify describing him as the founder of astrophysics" (PMM). Plate 2, reproducing Fraunhofer's map of the lines of the solar spectrum, is the FIRST ILLUSTRATION OF THE SOLAR SPECTRUM. Dibner 153; Norman 836; PMM 278a.