One of 41 bromide prints related to and showing various stages in the construction of the Hooker 100 inch reflecting telescope at Mount Wilson, California. This view shows the upper steel float of the telescope's polar axis being tested with compressed air. The lower float is also shown in position in the Mercury Trough. The observatory was founded in 1904 by the astronomer George Ellery Hale (1868-1938). The 100 inch reflecting telescope installed in 1917 was the largest telescope in the world at the time, and remained so until the 200 inch reflector at Mount Palomar became operational in 1948. Mount Wilson was at the forefront of astronomy in the first half of the 20th century. Observations by astronomers working there confirmed that the Universe was expanding, as well as leading to substantial advances in understanding of the workings of the Sun.
© Science Museum / Science & Society Picture Library