Welcome Your IET account
Shackleton’s Endurance trapped in the Antarctic pack-ice

The whole story of exploration: part two, age of instruments

Image credit: Diomedia, Getty Images, Alamy, Dreamstime

In the 19th century, attention shifted from nautical expeditions to terrestrial surveying, and the theodolite became a vital instrument of economic and colonial expansion.

The ability to know the time in two places at once had a massive effect on exploration, especially at sea, because it led to an immense improvement in the accuracy of maps. Captain Cook had been among the great innovators in this field, brought about by the fact that his voyages of discovery had been primarily for the benefit of science, rather than the establishments of trade routes. The improvement in accuracy was exploited by the mutineers on the Bounty, whose ringleader Fletcher Christian deliberately chose the tiny island of Pitcairn in the Pacific Ocean as a refuge, precisely because it had been wrongly positioned on Admiralty charts; he ‘rediscovered’ Pitcairn some 188 nautical miles (216 miles) east of its recorded position. Such was his confidence in this discrepancy, he was prepared to gamble that, no matter how hard the Royal Navy searched, the likelihood of mutineers being tracked down was minimal. At the time, there were large areas of the Pacific that hadn’t been mapped at all.

By the dawn of the 19th century, there was a shift from political interest in geographical knowledge of the world’s oceans to a commoditised, commercialised obsession with its land. As the British Empire grew, focus turned to India and the Great Trigonometrical Survey, which aimed to measure the sub-continent with scientific precision. “What we’ve been talking about up until now has been nautical navigation, but on land the great development was the optical angle-measuring instrument, the theodolite,” says the Royal Geographical Society’s Eugene Rae. “As Britain came to control India, it needed detailed knowledge of the terrain for military purposes.” Yet more importantly, the government needed to know where everything was in order to tax it. “Taxation was the big thing. We’ve moved into an age of money and materials.” India had become a vital cash resource to India. Although the first imperial factories started to appear in India in the 17th century, by the Victorian age it was a boom era.

The survey was carried out by a process called triangulation, which, despite appearing rudimentary – men with chains and poles manually casting a geometrical mesh over the terrain to make their measurements – got the job done. “But when they got to the mountainous north of India,” says Rae, the system showed its limitations, and the surveyors were forced to build “enormous rock towers on which to mount their massive theodolites in order to map the Himalayas”. By 1856, there was the first estimate of the height of Mount Everest: “They reckoned it was 29,002ft, which is pretty accurate.” Today’s official elevation of the mountain – named after Sir George Everest, Surveyor General of India 1830-43 – is 29,028ft (8,848m). By contrast, surveying in Africa was less advanced: compasses and sextants were still the order of the day.

Observation with the theodolite on the Fridtjof Nansen’s Fram expedition to the North Pole 1893-1896

Image credit: Diomedia, Getty Images, Alamy, Dreamstime

Yet the 19th century was also the ‘age of the gadget’, the most interesting of which, reckons Rae, was the ‘artificial horizon’. Until now, to use navigational instruments such as a sextant, “you needed to be able to see the horizon, meaning that on land, in a forested or mountainous area, you can’t accurately use your sextant”. The way explorers got around this was “to look for a shallow pool of water and then point their sextant to the water at 45 degrees and take their reading from the reflection of a celestial body. If you double the reading, you come up with the same reading as if you’d worked with a natural horizon.” Knowing the principle, explorers started to take mirrors with them on expeditions. This quickly evolved into a mercury-based instrument consisting of a metal tray with a triangular lid in which are set glass panes.

Other instruments such as portable hypsometers (for measuring elevation), manometers (pressure), thermometers, barometers and so on all became indispensable tools of the exploration trade. Yet perhaps as significant to the expedition process as the theodolite was the photographic camera. “But before the camera proper,” says Rae, “there’s a device called a camera receder, basically an instrument that helped accuracy in drawing. It had lenses and could project an image of, say, a mountain, on to a piece of paper. The explorer Thomas Atkinson, who travelled in Central Asia in the 1850s, mentions these in his diaries.” However, early cameras were the breakthrough, as they returned irrefutable pictorial truth home from the field. These came at a cost: early polar photographers such as Frank Hurley used heavy glass plates, many of which had to be abandoned in Antarctica after the loss of Shackleton’s ship Endurance. Field cameras and later interlocking box (or nested tube) models weighed several kilos and required enormous tripods to provide stability for the long exposures required by the pre-film silver bromide gelatin dry plates measuring 6.5 x 8.5in.

Despite these disadvantages, explorer technology was starting to become recognisable from today’s perspective. With the internal combustion engine making its way into vehicles suited for exploration, the 20th century beckoned.

Surveying

The rise of the theodolite

A staple of land surveying, the theodolite has been with us since Dutch cartographer Gemma Frisius introduced graphical triangulation in the first half of the 16th century. When a century later another Dutch scientist Willebrord Snellius introduced numerical triangulation, the way was paved for a future of surveying that was to include stereo aerial photography, infrared and intelligent theodolites. 
While there is no consensus on what the word means (the optical term ‘diopter’ was originally used as a synonym), it is thought to derive from two Greek words that add up to the expression ‘to look upon clearly’. The theodolite really started to make inroads in the period 1784-1853, when units made by the British scientific instrument maker Jesse Ramsden were used as part of a programme of high-precision geodesic surveys in southern Britain.
The mid-19th century saw a surge in theodolite manufacture, when it became popular with US railway engineers. Today’s digital theodolites are electronic transit theodolites with integrated electronic distance measurement and are called total stations, with calculations performed on an on-board computer.

Sign up to the E&T News e-mail to get great stories like this delivered to your inbox every day.

Recent articles

Info Message

We use cookies to give you the best online experience. Please let us know if you agree to all of these cookies.


Learn more about IET cookies and how to control them