Spectrum of both these tubes described.
Both these tubes, when examined with the spectroscope, showed four bright rather uniform bands (the central one being the brightest), which I assigned to the carbon-spectra (see Plate XIV. spectra 5 and 6).
The Geissler tube was probably filled designedly with coal-gas. In the case of the barometer-tube the spectrum must be assumed to be the result of some carbon impurity.
No lines of mercury could be detected in either case.
An effort was made to examine the light of the Geissler mercury-tube as excited by motion only, but the spectrum could not be kept in the field; the four lines were, however, seen to flash out as the light passed before the slit.
Plate XV.
Air-tubes.
Air-tube illuminated.