III. On the effect of pressure on the character of the spectra of gases

The variations in the spectra of gases which accompany changes of density have been studied by Plücker and Hittorf, Frankland and Lockyer, Wüllner and others. It appears to us that one cause to which these changes may be due has been overlooked, and that many of the observed variations are entirely independent of the density of the gas. If a Leyden jar be placed in the circuit, and the current from an induction-coil be passed through a Plücker’s tube containing nitrogen with the traces of hydrogen generally present, the following well-known phenomena are observed.