Formerly the sparkand absorption-spectra were the sole methods available; a third method was introduced by Crookes, who submitted the oxides, or preferably the basic sulphates, to the action of a negative electric discharge in vacuo, and investigated the phosphorescence induced spectroscopically.
When the substance to be examined spectroscopically is in solution the spark may be taken from the solution, which must then be used as kathode of air.
He employed in his discussion the radial velocities of 280 stars, spectroscopically determined; and the upshot signally exemplified the community of interests between the rising science of astrophysics and the ancient science of astrometry.
Hartwig in 1885, and subsequently spectroscopically examined by many observers; R Andromedae, a regularly variable star; and the Andromedids, a meteoric swarm, associated with Biela's comet, and having their radiant in this constellation (see Meteor).