Solar, Gas-Flame, and Electric-Light Spectra

Abstract

IN answer to Mr. J. Hopkins Walters' inquiry contained in NATURE, vol. xxv. p. 103, the spectroscope declares that all these three spectra have for their base a continuous strip or band of light; in the case of gas-flame (the bright part) crossed by the sodium lines only; in that of the sun by the well-known Frauenhofer dark lines; and of the electric (arc) light by the bright lines of carbon. The illuminating power of each of these sources of light is thus shown to be due to the incandescence of their several solid and gaseous constituents, concerning which a volume might be written. The relative effect of the sun's bright golden glare, the gas-flame's duller yellow tint, and the electric-light's moon-like whiteness, on the optic nerve; have not, as far as I am aware, been yet made the subject of special research. Popular opinion assigns injurious results to the whiter light. Mr. Walters will find in “Photographed Spectra,” on Pl. xv., Fig. 4, and the extra plate, the solar spectrum, and on Pl. v., Figs. 3 and 4, the spectrum of the electric arc between carbon points specially prepared to insure purity. In Dr. Marshall Watt's “Index of Spectra” the spectrum of the blue base of candle-flame is represented by the graphical diagram and description, Carbon I. The illuminating portion of a gas-flame presents in the spectroscope the appearance of a dull sun spectrum without the dark lines.