Trivial name for example, hydrogen ("water-producing"), oxygen ("acid-producing"), nitrogen ("soda-producing"), bromine ("stink"), and argon ("no reaction") were based on Greek roots, while the names of iodine and chlorine were derived from the Greek words for their characteristic colors. Indium, rubidium, and thallium were similarly named for the colors of particular lines in their emission spectra. Iridium, which forms compounds of many different colors, takes its name from "iris", the Latin for "rainbow". The noble gases have all been named for their origin or properties. Helium comes from the Greek "helios", meaning "sun" because it was first detected as a line in the
Westward the Course of Empire Takes Its Way in the Rocky Mountains" that was part of the 1898 Trans-Mississippi Issue, and reprinted a century later. A Currier and Ives print from 1868 uses the same title and theme for a very different print, showing a railroad crossing a new settlement as the train goes west. A and a stereograph by Alexander Gardner, both of an 1867 end-of-track frontier construction train, were titled "Westward The Course of Empire Takes Its Way". David Foster Wallace named one of his short stories "Westward the Course of Empire Takes Its Way" in his 1989 collection "Girl with Curious Hair". Early revisions of