Holmium spectral lines

Hohnium oxide occurs in nature, usually associated with small quantities of other rare-earth oxides. Commercial applications of this compound have not been explored fuUy. It is used in refractories and as a catalyst. Characteristic spectral emission lines of holmium oxide glass are used to cahbrate spectrophotometers. ... 

Discovery During 1878-79, PerT. Cleve in Uppsala discovered that erbium contained two other elements. He named them thulium after the old Roman name Thulia for the Furthest North and holmium after Stockholm. Delafontaine and Soret in Switzerland had in fact found lines of a foreign element during the spectral analysis of erbium in 1878. This element, erbium-X or element-X, appeared to be identical with holmium. In tables of discoverers Delafontaine and Soret are mentioned alongside Cleve. 

---