Right on time.In the era before global positioning system Global Positioning System: see navigation satellite. Global Positioning System (GPS) Precise satellite-based navigation and location system originally developed for U.S. military use. (GPS) instruments, determining longitude longitude (lŏn`jĭt  d'), angular distance on the earth's surface measured along any latitude line such as the equator east or west of the prime meridian. was difficult since it required a fairly accurate clock, in addition to a sextant sextant, instrument for measuring the altitude of the sun or another celestial body; such measurements can then be used to determine the observer's geographical position or for other navigational, surveying, or astronomical applications. ("North vs. Northwest: Lewis and Clark diaries provide directional clue," SN: 10/4/03,p. 213). I was under the impression that one of the clocks Lewis and Clark used was Jupiter's moon Io, which would have made them pretty sophisticated navigators. MICHAEL D. DELANO, BROOKLYN, N.Y. The explorers had a good chronometer chronometer (krənŏm`ətər), instrument for keeping highly accurate time, used especially in navigation. Before the advent of radio time signals it was the only device that provided the time accurately enough for a ship at sea to , but researcher Robert E. Criss says that not much more is known about it because it was auctioned off after the trip. He didn't find any mention in the party's diaries of Jupiter's moon, but the team did rely on Earth's moon for some measurements. K. RAMSAYER |
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