PRITCHARD, CHARLES

(b. Alberbury, Shropshire, England, 29 February 1808; d. Oxford, England, 28 May 1893)

astronomy, astrophysics.

Various dates have been given for Pritchard’s birth; 29 February 1808 seems the most likely. Pritchard graduated from Cambridge in 1830 and soon afterward moved to London, where he helped found Clapham Grammar School. He remained in charge of the school until 1862, when he retired to the Isle of Wight. While in London, Pritchard developed an interest in astronomy and erected an observatory at Clapham Grammar School. But although he became an influential member of the Royal Astronomical Society, serving as president in 1866-1868, he had no major research to his credit when, in 1870, he was appointed Savilian professor of astronomy at Oxford. Pritchard persuaded the university to provide funds for building an observatory on the edge of the University Parks. When the observatory was completed, it was partly equipped by Warren de la Rue, who donated his own instruments.

The most important aspect of Pritchard’s work at Oxford was his role in convincing the astronomical community that accurate measurements of position could be obtained from photographic plates. One of the first programs he undertook—at de la Rue’s suggestion—was an attempt to determine the lunar librations from photographs of the moon. The final results apparently were never published, but a paper on the moon’s diameter did appear. Pritchard next stressed the possibility of using photography for the determination of stellar parallaxes. He made detailed parallax observations of a few stars, including 61 Cygni, but also employed the method in a more wholesale form to derive an average parallax for all stars of the second magnitude visible at Oxford. The latter measurements received some criticism, but J. Kapteyn subsequently followed a quite similar approach in his much more extensive and important investigations.

Pritchard’s other major project at Oxford was photometric. He devised a program for measuring the magnitudes of all naked-eye stars up to 100° from the North Pole using a wedge photometer. The results, published in 1886 as Uranometria nova Oxoniensis, paralleled work carried out not long before at the Harvard College Observatory. Agreement between the two sets of results was quite good, thus providing a generally acceptable magnitude sequence for the brighter stars.

During his time at Oxford, Pritchard was also involved in a number of researches of lesser importance such as the determination of a few double star orbits. Although dependent in all these investigations on research assistants for help, he personally participated in the work as well. He remains one of the very few scientists who carried out all his important research work after the age of sixty.

BIBLIOGRAPHY

There is a detailed obituary of Pritchard in Proceedings of the Royal Society, 54 (1893), iii-xii, which contains a representative list of his more important papers. His daughter, Ada Pritchard, subsequently published a biography, The Life and Work of Charles Pritchard (London, 1897).

A. J. Meadows