2. “Eisenlohr,” iˈzen-lore. (1799-1872.) A German physicist. He was a Heidelburg student, and in 1819 removed to Mannheim, where he became a teacher of mathematical and physical science in the lyceum. He was afterward a professor at Carlsruhe. A Manual of Physics is his chief work. 3. “Geissler’s tubes,” ghīceˈler. The spectrum of any gas can be best obtained by placing the gas in these tubes, and then passing the electric current through. If the gas is hydrogen, the spectrum will consist of a bright red, a green, and a blue line. Each gas casts its own spectrum. In this way the spectroscope aids in the analysis of substances. The different spectra formed reveal the elements. 4. “Sir John Herschel.” (1792-1871.) An English astronomer. His great enterprise was his expedition to the Cape of Good Hope to take observations of the heavens in the southern hemisphere. He remained there four years. His published results of his observations furnish one of the most valuable works on astronomy. He did not confine his studies to astronomy alone, but gave great attention to the subject of the atmosphere. He held that from eighty to ninety miles above the earth a perfect vacuum exists, and that three fourths of all the atmospheric air lies within four miles from the earth’s surface. His studies in meteorology were also very valuable, as well as his important discoveries in photography. Among his published works are: “Essays, from the _Edinburgh_ and _Quarterly Reviews_, with Addresses and Other Pieces,” “Physical Geography,” and “Familiar Letters on Scientific Subjects.” Herschel held various positions of honor in his lifetime, being at one time president of the Royal Astronomical Society, and afterward Master of the Mint for five years. He was one of the eight foreign associates of the French Academy of Sciences. 5. “Fire Worshipers.” A Persian sect which worships fire as an emanation of the divine being. “Fire worshipers” is the English name for the Guēˈbers (also called Ghēˈber or Giaours—jours). They call themselves _Beh Din_, “those of excellent belief.” The Arabs completed the conquest of Persia in the seventh century, and the great mass of the nation adopted the faith of the conquerors. Those who refused to do so were subjected to persecution. Some of them took refuge in the wilderness of Khorasan, and others in Kohistan. The latter in the ninth century emigrated to India and settled in the neighborhood of Surat. Their descendants still inhabit the same region, and are called Parsees. The descendants of those who remained in Persia have gradually decreased in numbers and sunk into ignorance and poverty, though still preserving a reputation for honesty, chastity, industry, and obedience to law superior to that of the other Persians. They are estimated to number about 7,000.