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Close up of transit eyepiece

Astronomy in the British Empire was not just about star-watching from observatories and ships. In the colonies, astronomy was also an essential part of the ‘survey sciences’—a diverse range of geographical practices deployed to chart territory in the service of imperial settlement and administration.

This took astronomers out into the field as part of projects like the ‘Great Trigonometrical Survey of India’, a vast scientific and military undertaking to measure and map the entire Indian subcontinent.

An empire of science

This map shows the extraordinary scale of the ‘Great Trigonometrical Survey of India’, by far the largest and most complex land survey ever conducted in the British Empire.

The circles, crosses, and stars show the pendulum and astronomical stations that made up the Survey’s reference points. Each triangle is the calculated result of numerous angle and baseline measurements taken by teams of surveyors between 1802 and 1870.

The ‘survey sciences’ served in the front lines of the East India Company’s territorial conquest of India. Backed by British military power, surveyors worked for nearly a century to extend cartographic control—and with it administrative authority—across South Asia. As Clements Markham, Secretary of the Royal Geographical Society, haughtily declared in 1871:

“The story of the Great Trigonometrical Survey, when fitly told, will form one of the proudest pages in the history of English domination in the east.”(1)

Great theodolites

12-inch theodolite, by Troughton & Simms
Image 1: 12-inch theodolite, by Troughton & Simms, London, 1898 (Wh.2583).

Theodolites like the example shown in Image 1 were an important tool for 18th- and 19th-century imperial land surveys, particularly for triangulation.

In this technique, the telescopic sight was used to accurately measure horizontal and vertical angles between distant vantage points; their relative locations could then be calculated using trigonometry.

Despite requiring at least two people to lift it, for serious survey work an instrument the size of the Whipple’s example would have been considered small. Increased accuracy in angular measurement is best achieved by making the circular measuring scales larger.

The ‘Great Theodolites’ used in the Great Trigonometrical Survey of India had a horizontal scale three feet in diameter and weighed over half a tonne, requiring a dozen strong men to carry them.

As the military surveyor J. A. Hodgson noted in 1822, this kind of instrument was only ‘portable’ because of the colonisers’ access to plentiful local manpower:

“In Instruments intended for India, solidity should be considered; we want those which will do their work effectually, and are not anxious that they should be small and easily portable, as we can always here find means of carrying them.”(2)

Read more: Survey instruments in India

Struggling in the field

Everest theodolite, by Troughton and Simms
Image 2: Everest theodolite, by Troughton and Simms, London, c. 1880 (Wh.1877)

Surveys and expeditions relied upon large quantities of instrumentation surviving transportation and use in often harsh environments.

George Everest, the sixth Surveyor General of India, wrote that instruments needed to be secured against “a puff of wind or a careless native,” and designed the rugged, compact theodolite shown in Image 2 with Indian survey work in mind.

Despite efforts to guard instruments against field conditions, surveyors’ own accounts are filled with complaints like that of Edward Garstin:

“I have one of the best levelling instruments in India … but owing to the negligence of my servants the stand is lost. … Although I have the theodolite which the liberality of Government formerly gave me to replace the instrument I brought from Europe and lost on service, yet it is so very bad an instrument that it is useless, as no possible adjustment can make it correct enough to ... place the smallest dependence on it.”(3)

Garstin and his fellow surveyors frequently described their equipment as fragile, erratic, and easily lost, or blamed local collaborators and servants for mishandling objects and hampering work. And they often highlighted their own particular skills at coaxing wayward instruments back into working order.

Such reports drew attention to surveyors’ triumph over adversity, and furnished excuses when data was deficient or incomplete.


1.     Clements Markham, A Memoir on the Indian Surveys (London: 1871), p.124.

2.     J. A. Hodgson, ‘Journal of a Survey to the Heads of the Rivers, Ganges and Jumna’, Asiatick Researches, Vol. 14 (1822), 60–152, on p.102.

3.     Edward Garstin, letter to superiors at the Survey of India office, 13 Sep. 1820, as quoted in: R. H. Phillimore, Historical Records of the Survey of India, Vol. 3 (Dehra Dun: Survey of India, 1954), on p.212.


Joshua Nall

Joshua Nall, ‘Science in the Field’, Explore Whipple Collections, Whipple Museum of the History of Science, University of Cambridge, 2020.

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