Astronomical Spectroscope

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This is a spectroscope, designed to be used with a telescope to study the light of the sun. It was made in Dublin in 1877 by the famous instrument maker Howard Grubb (1844–1931). It was used with the 9 ½ inch Alvan Clark & Sons refractor in the Observatory of Princeton University.
When the College of New Jersey at Princeton hired the astronomer Charles A. Young in 1877, they also gave him funds to equip the new John C. Green student observatory. One of his first purchases was this instrument. It was custom-made, and Young helped refine the design. (Grubb's company later advertised that this was the first such spectroscope that they had sold.) The most unusual feature of this instrument is the use of a complicated system of multiple prisms to disperse the light and produce a highly detailed view of the solar spectrum.
In use, the spectroscope was mounted at the eyepiece end of the telescope and light from the sun would be directed through it. As the light passed from one prism into the next, it would be increasing dispersed, or spread out. To make the instrument more compact, the beam of light was directed first through the upper portion of the prisms and then back through the bottom part. Depending on how it was configured, the light could thus be passed through either 2, 4, 6 or 8 prisms. A particular area of the solar spectrum could be viewed by turning a small chain that moved each prism by the same amount. Because of the large number of optical surfaces involved, the light loss in this instrument was almost certainly in the 90 percent range. This was an advantage when viewing the Sun, but it reduced the usefulness of this instrument for other purposes, such as measuring the spectra of stars. The success of this instrument in making precise measurements of the solar spectrum (and thus revealing information about the composition of the sun and its atmosphere) led to its wider adoption as an important astronomical tool.
Currently not on view
date made
Young, Charles A.
Grubb, Howard
place made
Republic of Ireland: Leinster, Dublin, Dublin
place used
United States: New Jersey, Princeton University, Princeton University Observatory
overall: 22 1/2 in x 10 1/4 in x 9 in; 57.15 cm x 26.035 cm x 22.86 cm
overall in case: 9 in x 22 1/4 in x 10 3/8 in; 22.86 cm x 56.515 cm x 26.3525 cm
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Data Source
National Museum of American History