How Do We Measure the Height of a Mountain?
Most of our figures for mountain heights were obtained with an “altimeter.” This is kind of barometer that uses atmospheric pressure to measure altitude, or height above sea level. For more accurate measurements, surveyors use a technique called “topographic survey.”
With the help of mathematics and a special instrument known as a “transit,” which is used to measure angles, the surveyor makes the unknown height of a mountain part of an imaginary triangle. By calculating the length of that side of the triangle, the height of the mountain can be determined.
Before GPS technology was invented, geologists and cartographers assessed mountains with high-powered protractors called theodolites and transits. If you stand at some known distance away from a mountain and figure out the angle from where you are on the ground to the peak, then you can calculate its vertical height.
In the 19th century, British surveyors in the Great Trigonometrical Survey of India measured a certain very tall mountain at 29,002 feet as they triangulated their way across the subcontinent. Not bad, considering some of their readings were taken from 160 miles away. When an American expedition measured Mount Everest with GPS in 1999, scientists discovered the mountain was 33 feet higher, or 29,035 feet above sea level.