A diffraction grating is a plate engraved with a large number of fine parallel lines. They are used in spectroscopy to analyse the spectra of stars into their compound colours. Every element has a different signature spectrum, the spectroscope allows the observer to define what elements the object is composed of. Spectroscopy was first used in astronomy in the early 1860s. One of its first uses was to determine the elements that comprise the sun. Star spectroscopes can allow a user to determine the composition of a celestial object, its motion, density, and temperature.
Henry Augustus Rowland (1848-1901) invented a ruling engine in 1882 that produced a grating of high resolution and accuracy. He was awarded the gold medal at the 1890 Paris Exhibition for the grating. His invention allowed him to re map the solar spectrum more accurately than had ever been done before. The Rowland gratings became the standard instruments for spectroscopic work throughout the world.
Thomas Thorp developed his celluloid diffraction grating replicas, which he made from an original Rowland Grating, and brought high resolution spectroscopy within the reach of the amateur.
This device was used at Sydney Observatory for demonstration purposes. It remains of national significance due to its pioneering role in Australian science and its association with Australia's earliest astronomers.
Stuewer, R.H., 'Henry Rowland:the ruler of the grating', Physics World, July 2001, p.47.
Gerard LeTurner, 19th Century Scientific Instruments, Sotheby Publications, 1983, pg 160
Written by Erika Dicker
Assistant Curator, February 2008