Page:Popular Science Monthly Volume 33.djvu/270

258 the spectral bands of the electric arc (which are identical with those of the candle and the oxyhydrogen blow-pipe) may be carried, I have published a specimen of the facies of the yellow, green, and blue bands, indicating the intensity and normal distance of the rays composing them. It appears, from this work, that, for a fifth part alone of their total length, these bands show, respectively, 163, 160, and 120 lines; this would bring to about 800 the number of lines constituting each band, and to at least 4,000 the number of the lines forming the five bands of the spectrum of the electric arc; for the more intense bright lines are doubled again when they are observed under conditions favorable to their brilliancy and dispersion. In comparing, with the same spectroscope, the spectrum of the electric arc and the solar spectrum, we observe that the former spectrum displays a more considerable number of bright rays than the solar spectrum of dark rays. Since it is nearly certain that the spectral bands belong to the spectrum of carbon—for they are observed when the electric arc shines in a vacuum, that is, when carbon alone is in ignition—it follows that the spectrum of this element contains more rays than the entire solar spectrum.

Some physicists doubted for a long time the identity of the spectra of carbon and the candle-flame, because there existed a spectrum of carbon entirely different from the banded spectrum. But as I have succeeded in demonstrating, on the one hand, that this spectrum does not belong to carbon, and on the other hand that the spectrum of the candle-flame was brightly visible in the ignited filament of the incandescent lamp when the vacuum is as perfect as it is possible to make it, I think there should now be little doubt respecting the identity of the two spectra. Carbon, being found in various combinations everywhere on the surface of the globe, should of necessity reveal its presence in most of the bodies subjected to spectrum analysis. Eminent chemists have even found traces of it in the nearly perfect vacuum of our pneumatic machines.

The absorption spectrum of carbon, or that which should be composed of the dark lines detaching themselves upon a continuously bright spectrum, has not yet been obtained. In the comparative study that I have made of the solar spectrum and the spectrum of carbon, I have shown that most of the bright rays forming the carbon bands do not coincide with the dark rays of the solar spectrum. I have been inclined to believe from this that the absorption spectrum of carbon does not exist in the solar spectrum, but I have not been able to declare the same conclusion respecting the emission spectrum—that is, the spectrum with bright bands—because the discovery of the bright bands in the solar spectrum offers a real difficulty, resulting from the fact