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24-inch Bruce doublet photographic telescope optics
Date: 1890-1893
Inventory Number: 2016-1-0044
Classification: Objective
Subject:
Maker: Alvan Clark and Sons (1846 - 1958)
User: Henrietta S. Leavitt (1868 - 1921)
User: Edward C. Pickering (1846 - 1919)
User: Oak Ridge Station (1931 - 2005)
User: George R. Agassiz Station, Harvard (1951 - 1982)
User: Harvard College Observatory (founded 1839)
Cultural Region:
City of Use:
Dimensions:
optical assemblage as displayed spread out : 74.9 × 74.9 × 116.8 cm (29 1/2 × 29 1/2 × 46 in.)
For detailed measurements of each element, see description.
Description2016-1-0044 is the assemblage of optics for the 24-inch aperture Bruce photographic telescope. This telescope was a "doublet doublet"--that is to say, instead of having just one doublet lens (consisting of crown and flint glass elements), it had two doublet lenses. The lens elements are labeled from the sky-facing end as follows:
2016-1-0044a Element 1, crown lens, biconvex
2016-1-0044b Element 2, flint lens, biconcave
2016-1-0044c Element 3, flint lens, convex-concave
2016-1-0044d Element 4, crown lens, biconvex
In front of the lenses, there was an objective prism that could be taken on and off.
2016-1-0044e Objective Prism, 4°
Each glass element is about 25 inches in diameter. Each has its own cast iron cell and brass retaining ring.
TECHNICAL DETAILS
Element 1 (2016-1-0044a)
crown glass, biconvex
edge thickness: 0.810 in
OD: 25.110 in
front radius: 72.80 in
rear radius: 55.57 in
weight of glass: 91.4 lbs
cell OD: 28 in
weight of cell and ring: 49.4 lbs
Element 2 (2016-1-0044b)
flint glass, biconcave
edge thickness: 2.428 in
OD: 25.062 in
front radius: 54.91 in
rear radius: 762.3 in
weight of glass: 90.1 lbs
cell OD: 28 in
weight of cell and ring: 42.7 lbs
Element 3 (2016-1-0044c)
flint glass, convex-concave
edge thickness: 1.86 in
OD: 25.13 in
front radius: 140.71 in
rear radius: 50.17 in
weight of glass: 73.4 lbs
cell OD: 28 in
weight of cell and ring: 61.9 lbs
Element 4 (2016-1-0044d)
crown glass, biconvex
edge thickness: 0.62 in
OD: 25.110 in
front radius: 61.84 in
rear radius: 198.9 in
weight of glass: 63.5 lbs
cell OD: 28 in
weight of cell and ring: 51.6 lbs
Objective Prism (2016-1-0044e)
angle 4°
OD: 25.571 in
weight of glass: 90.4 lbs
cell OD: 29.5 in
weight of cell and retainer: 102.9
Total weight of all glass: 408.8 lbs
Total weight of cells: 308.5 lbs
2016-1-0044a Element 1, crown lens, biconvex
2016-1-0044b Element 2, flint lens, biconcave
2016-1-0044c Element 3, flint lens, convex-concave
2016-1-0044d Element 4, crown lens, biconvex
In front of the lenses, there was an objective prism that could be taken on and off.
2016-1-0044e Objective Prism, 4°
Each glass element is about 25 inches in diameter. Each has its own cast iron cell and brass retaining ring.
TECHNICAL DETAILS
Element 1 (2016-1-0044a)
crown glass, biconvex
edge thickness: 0.810 in
OD: 25.110 in
front radius: 72.80 in
rear radius: 55.57 in
weight of glass: 91.4 lbs
cell OD: 28 in
weight of cell and ring: 49.4 lbs
Element 2 (2016-1-0044b)
flint glass, biconcave
edge thickness: 2.428 in
OD: 25.062 in
front radius: 54.91 in
rear radius: 762.3 in
weight of glass: 90.1 lbs
cell OD: 28 in
weight of cell and ring: 42.7 lbs
Element 3 (2016-1-0044c)
flint glass, convex-concave
edge thickness: 1.86 in
OD: 25.13 in
front radius: 140.71 in
rear radius: 50.17 in
weight of glass: 73.4 lbs
cell OD: 28 in
weight of cell and ring: 61.9 lbs
Element 4 (2016-1-0044d)
crown glass, biconvex
edge thickness: 0.62 in
OD: 25.110 in
front radius: 61.84 in
rear radius: 198.9 in
weight of glass: 63.5 lbs
cell OD: 28 in
weight of cell and ring: 51.6 lbs
Objective Prism (2016-1-0044e)
angle 4°
OD: 25.571 in
weight of glass: 90.4 lbs
cell OD: 29.5 in
weight of cell and retainer: 102.9
Total weight of all glass: 408.8 lbs
Total weight of cells: 308.5 lbs
Signedunsigned
Historical AttributesThe Bruce photographic telescope was the most powerful telescope in the world when it was completed in 1893. Made by Alvan Clark & Sons of Cambridge, Massachusetts, the telescope had two pairs of massive glass lenses with a clear aperture of 24 inches and a combined focal length of 11 feet. In front was a removable prism for dispersing starlight into spectra. The telescope was sent by the Harvard College Observatory to Arequipa, Peru and then to Bloemfontein, South Africa in order to photograph the southern sky on giant glass plates. More sensitive than the naked eye, the photographic plates revealed the existence of hundreds of thousands of unknown stars and galaxies.
The Bruce telescope took 27,504 photographic plates, which were 14 x 17 inches and 8 x 10 inches. The scale was 60 inches / mm. The plate series was labeled "A."
Plates
1- 1730 Cambridge 9 November 1893 - 21 October 1895
1731-14110 Arequipa 2 April 1896 - 6 November 1926
14111-27504 Bloemfontein 15 July 1929 - 11 October 1950
The Bruce plates are in the Harvard Observatory Plate Stacks.
Many of the Arequipa astronomical photographs were analyzed by Henrietta Swan Leavitt at Harvard College Observatory. Leavitt was a “computer” who specialized in variable stars. Her analysis of a special class (known as Cepheid variables) in the Magellanic Clouds led to her discovery of a law connecting the absolute magnitude of each such star with the period that its brightness fluctuated. Published in 1908 and 1912, Leavitt’s findings would soon be used as a way to measure the dimensions of the universe.
Astronomers had thought that the Milky Way was the entire universe. But in the 1920s, Edwin Hubble, using a 100-inch telescope at Mount Wilson, discovered Cepheid variable stars in spiral nebulae within the Milky Way. The variable stars served as “standard candles.” Since their absolute magnitudes were known from their periodic fluctuations, their apparent dimness in photographs had to be due to a great distance between us and them. This led to the conclusion that nebulae were independent galaxies located far beyond the Milky Way. This discovery was followed by the realization that the universe was expanding.
The Bruce telescope took 27,504 photographic plates, which were 14 x 17 inches and 8 x 10 inches. The scale was 60 inches / mm. The plate series was labeled "A."
Plates
1- 1730 Cambridge 9 November 1893 - 21 October 1895
1731-14110 Arequipa 2 April 1896 - 6 November 1926
14111-27504 Bloemfontein 15 July 1929 - 11 October 1950
The Bruce plates are in the Harvard Observatory Plate Stacks.
Many of the Arequipa astronomical photographs were analyzed by Henrietta Swan Leavitt at Harvard College Observatory. Leavitt was a “computer” who specialized in variable stars. Her analysis of a special class (known as Cepheid variables) in the Magellanic Clouds led to her discovery of a law connecting the absolute magnitude of each such star with the period that its brightness fluctuated. Published in 1908 and 1912, Leavitt’s findings would soon be used as a way to measure the dimensions of the universe.
Astronomers had thought that the Milky Way was the entire universe. But in the 1920s, Edwin Hubble, using a 100-inch telescope at Mount Wilson, discovered Cepheid variable stars in spiral nebulae within the Milky Way. The variable stars served as “standard candles.” Since their absolute magnitudes were known from their periodic fluctuations, their apparent dimness in photographs had to be due to a great distance between us and them. This led to the conclusion that nebulae were independent galaxies located far beyond the Milky Way. This discovery was followed by the realization that the universe was expanding.
Curatorial RemarksEach lens element and the prism was packed in a separate crate, found at Oak Ridge Observatory. The cells were attached to the optical tube, which was divided into two crates in a separate building at Oak Ridge. The cells were removed, restored, and reunited with the glass elements. The tube was left behind but photographically documented in its crates. Samples of the lens crates were preserved and accessioned.
ProvenanceOak Ridge Observatory, Harvard, MA., Building 16 and the Garage; transferred to CHSI, 2016.
