The Lick Observatory, California, USA, 1915.

Photograph by the Warner & Swasey Co of the Lick Observatory on Mount Hamilton, near San Jose, California. At an altitude of 4250 feet, this was the first permanent mountaintop observatory to be established when it was completed in 1888. The astronomer Charles Piazzi Smyth (1819-1900) was the first to demonstrate the benefits of placing a telescope at high altitude. In 1856, he set up temporary observatories on the mountains of Tenerife in the Canary Isles. These mountaintop sites provided stable air conditions, unlike the turbulent atmosphere found at lower altitudes which distorted an astronomer's view of the sky. Today, the world's largest telescopes are located at special mountain sites as they offer superior observing conditions to those found at sea level.