Enter Colonel William Lambton, a British surveyor. It was the year 1802 and the country was our very own India. Lambton began one of the greatest journeys ever undertaken in scientific history just to answer the above question. It was a journey that spanned 41 years, through the length and breadth of colonial India, in which thousands of lives were lost and which resulted in the comprehensive mapping of India and the revelation that the Himalayas, and not the Andes, were the tallest mountain range in the world.

We’re talking about the Great Arc experiment, also called the Great Trigonometrical Survey of India (GTS), which became possible thanks to the passion of two men — Lambton and Colonel George Everest, after whom Mt Everest was named — and their merry band of followers.

BUT WHATISANARC?
Now, an arc is part of a latitude or longitude that has been accurately measured physically on the ground and mapped. Lambert knew that if he determined the length of an arc along a chosen longitude at a one-degree latitude separation, then the length of that arc would be less near the equatorial latitudes than at the poles if the Earth were a spheroid. The bigger the arc, the more the accurate findings.

Earth's like an orange...

..because of its spinning motion, it bulges at the middle and flattens at the ends (like an orange) to become a "spheroid".

TRIANGLES TOTHERESCUE
So Lambton employed the technique of triangulation to achieve his goal. In triangulation, you have to identify three visible reference points at a height as the corners of a triangle. Knowing the exact distance between two of these points, and then measuring the angles made at each by the respective lines of sight with the third reference point, the distance and position of the third point can be deduced by trigonometry.

One of the sides of this triangle can now serve as the baseline for a second triangle that will include a new reference point. Then that triangle could lead to another triangle and so on. Lambert decided to make a chain of such triangles all across India! The spinal column of this triangular skeleton was the Great Arc, which not only settled the spheroid debate, but laid the foundations for a comprehensive map of the country.

WARS, FLOODS AND DYSENTRY
Lambton and his troupe of intrepid surveyors equipped with carriages, palanquins, tents and a massive half-tonne theodolite (an instrument to measure the angles of the triangles) began their gigantic quest on April 10, 1802, with the first baseline measurement between St Thomas Mount in Madras and a spot 7.5 km to its south. That measurement alone took 57 days!

The total north-south distance of 2,575 km was the longest measurement of the earth's surface ever attempted. The average length of a side of subsequent triangulations was 50 kms, the maximum being about 100 kms!

Imagine doing this in nineteenth century India without any of the modern-day facilities. Trees and houses had to be cleared to get the line of sight right. Sometimes whole villages had to be razed. Then there were malarial fevers, dysentery, floods, extreme weathers, treacherous hills, thick jungles and swamps, dacoity, snakebites and even battles. Plodding through nineteenth century India through all that must have been a Herculean task. And all the observations had to be done on top of tall structures like the tops of hills and temple gopurams. When these weren’t present, 30-metre high bamboo structures had to be erected.

LAMBTON AND EVEREST
In 1818, George Everest joined Lambton, and together they convinced a sceptical British government that the project should go on and parleyed with local kings to allow them to pass through their land. If Lambton went on relentlessly despite fever and dysentery, Everest fought through his paralysis.

Then at the age of 70 in 1823, Lambton died before he could fulfill his dream in a place called Hinganghat on his way to Nagpur. He is still lies buried there today in an anonymous grave.

The mantle fell on Everest's shoulders, who proved an able successor. He conceived covering the length and breadth of the country by a 'gridiron' of triangular chains (see picture), as against a network of triangulations as conceived by Lambton. He took the survey to the foothills of the Himalayas in 1841. Add another two years for computation and the GTS was completed in 1843.

CHANGING OURWORLD
Lambton and Everest’s hard work continues to benefit us even today. The GTS is the foundation of all topographical surveys. All subsequent technological achievements in this field can be traced back to this.

Accurate map details are a boon for those involved in developmental and infrastructure activities. Even the entire network of roads, rail and telecommunications in the country is intricately linked with the topography through which these networks must go through.

The GTS data has also aided fields such as astronomy, geophysics, seismo-tectonics, revenue, contribution to war and natural disaster relief measures and even socio-economic development!

The humble triangle has made history and geography and proved that the earth is a spheroid!

Col Everest never saw Mt Everest. His successor, Surveyor-General Andrew Scott Waugh, observed and discovered the world's highest peak in 1852. Assisted by the survey's chief computer, Radhanath Sickdhar, its height was determined to be 8,840 metres (8848m is now the accepted height). Waugh named it after his predecessor for his contribution to the Great Arc Expedition.

The survey showed that the Himalayas were the highest mountain range in the world