CAI 1957 Thomas Earnshaw Marine Chronometer No 509

This object is obviously famous because of its association with Charles Darwin, the scientist who developed the theory of evolution and who first got the idea while on the 1831 voyage of the HMS Beagle, which is the ship this chronometer belonged to. But even aside from that–even if it had no connection with Darwin–this item might well warrant inclusion in this series in its own right. Chronometers are fascinating things, and they really did change the world in amazing ways.

If you’re on a ship at sea, finding your latitude is very easy: you can calculate it from the position of the sun off the horizon. Longitude, however, is much harder to figure out; to get it exactly right you need to know the exact time not only aboard ship, but in your home port. In the early days of horology (the making of clocks) this was impossible because clocks just weren’t accurate enough. In the late 18th century, however, John Harrison, a British clocksmith, developed the marine chronometer, the first timekeeping device capable of accuracy close enough to calculate longitude at sea. The story of how Harrison did this is an epic one, chronicled in the very good 1996 book Longitude, which was made into an A&E miniseries in 2000 starring Michael Gambon as Harrison. Historically and scientifically it was a great step forward in history: now explorers could accurately explore and map the whole earth in a way that wasn’t possible before.

The Beagle’s chronometer was among the second generation of timekeeping devices. This one was built by Thomas Earnshaw, a watchmaker of some repute in Britain. Captain Robert FitzRoy and his officers used it to calculate their position after the Beagle left Plymouth on December 27, 1831 for a scientific survey voyage around the world. On board was a 22-year-old graduate student, Charles Darwin, who thought he wanted to study geology. His observations of animals in the Galapagos Islands, however, in September 1835 piqued his interest. The rest is scientific history. Darwin published his groundbreaking thesis, The Origin of Species, in 1859, and the world has never been the same since.

The Beagle‘s chronometer is currently on display at the British Museum in London.

The photo of the chronometer of the Beagle is copyright (c) by the Trustees of the British Museum. I use it here in accordance with their terms of use.