Wikipedia:Today's featured list/June 17, 2013
The large number of chronometers carried by HMS Beagle, an Admiralty survey ship, were vital to her three missions, which included charting the coasts of South America and Australia. Chronometers were formerly essential to mariners for the accurate determination of longitude. Beagle's second voyage (1831–36) established a chain of linked reference points of known longitude encircling the globe for the first time. Beagle required large numbers of chronometers so that they could be compared with each other for accuracy and some would inevitably break down on such a long voyage. The expensive chronometers included some by famous makers such as John Arnold who coined this use of the term chronometer, Edward Dent who designed Big Ben, and Thomas Earnshaw who invented the spring detent escapement. Some of these chronometers were still in use on Royal Navy ships in the modern era, and at least one went down with a battleship in the First World War. However, only two have survived to the present time, including one in the British Museum (pictured). (Full list...)