Page:Popular Science Monthly Volume 33.djvu/269

Rh The bright envelope nearly all disappears, while the inner dark cone is considerably developed, reaches a very high temperature, and exhibits a spectrum identical with that of the outer cone of the original flame. The brightness of the spectral bands is augmented by the rising of the temperature, and two new luminous bands, a red and a violet one, become visible in the spectroscope. At this moment we recognize that these bands are composed of a series of rays or bright lines, separated from one another by dark spaces.

While performing the prismatic analysis of the inner cone of a gas-light flame fed with pure oxygen, M. Stas observed, with the same spectroscope, a spectrum sensibly different as to the number of rays constituting the bands, according as the observation was made upon the top of the inner cone, where the temperature is highest and sufficient to keep iridium in fusion, or on the front or the side of this inner cone. The physiognomies of these three spectra vary according to the spectroscope employed. If we use a spectroscope with direct vision and weak dispersion, we observe a spectrum resembling that of the candle flame; but,-with an instrument of more considerable dispersive power, the bands define themselves into brilliant rays, some fine, and others broad, having extremely clear edges. These facts, M. Stas remarks, inseparably connect the facies of the spectrum of the flame with its greater or less elevation of temperature, and with the analyzing instruments employed.

Although the luminous intensity of the inner cone of the oxyhydrogen-flame is quite weak, Mr. Piazzi Smyth has discovered more than 400 bright rays in the spectral bands of this cone; viz., 97 rays in the red, 94 in the yellow, 97 in the green, 107 in the blue, and 71 in the violet bands.

But it is the analysis of the electric arc, the light of which does not differ essentially from that of the candle—for it is also the result of the ignition of carbon—that shows us these spectral bands in all their splendor, and initiates us into the grand complexity of their constitution. Like a luminous ribbon passing insensibly from one shade to another with diminishing brilliancy, each band is composed of a considerable number of bright rays of different breadths, disposed with a wonderful symmetry, increasing with the power of the analyzing instrument and the luminous intensity of the electric arc; the broader bright rays doubling into finer rays, and new luminous rays appearing in the dark spaces that separate the bright rays. While these bright lines are not arranged rigorously in the same manner in each band, they nevertheless show a great resemblance in their grouping and spacing.

In order to show how far the resolution into bright lines of