David Rittenhouse. Oil on canvas, 1796, by Charles Willson Peale. The Art Experience.

Rittenhouse, David (8 Apr. 1732-26 June 1796), astronomer, mathematician, and maker of mathematical instruments, was born at Paper Mill Run near Germantown, Pennsylvania, the son of Matthias Rittenhouse, a farmer, and Elizabeth Williams. Naturally talented in mathematics and mechanics, Rittenhouse constructed a model of a water mill at the age of eight, a wooden clock at about the age of seventeen, and a brass clock a short time later. He was fascinated with mathematics from his early years but, with little opportunity for schooling, was largely self-taught from books on elementary arithmetic and geometry and a box of tools inherited from an uncle, David Williams, a skilled furniture maker. From a translation of Isaac Newton's Principia (1687) and other scientific works procured for him by a brother-in-law, he managed to obtain a sound knowledge of the physical sciences. Despite the limitations of his environment, Rittenhouse eventually developed a remarkable capability for theoretical and observational astronomy.

At the age of nineteen Rittenhouse constructed a shop on his father's farm along the road to Norriton. There he made additional tools required for his adopted trade of clockmaker and produced and sold a number of tall case clocks, three of which incorporated small orreries, as well as mathematical instruments. He successfully experimented with the expansion of steel and wood for the development of a compensated pendulum of his own design for regulating his clocks with greater accuracy.

Between 1756 and 1785 Rittenhouse made a variety of astronomical instruments, which were highly prized, including transit and equal altitude instruments, zenith sectors, and telescopes. Particularly interesting was a collimating telescope he invented for the purpose of adjusting instruments in the meridian when intervening structures prevented visibility of a distant mark. He was also the first in the United States to utilize spider web as the filament for cross hairs in the telescope's eyepiece. His other instruments included barometers, a pocket metallic thermometer, and at least one hygrometer. In 1786 he experimented with diffraction, which had been described in Newton's Opticks (1704) as "the inflection of light in passing near the surfaces of bodies," and designed a plane transmission grating, made of fine wire fitted into a frame, that resolved a problem in the inflexion of light. With one of these he was able to observe six orders of spectra and to formulate the law that governed their displacement.

By 1770 there was a constant market for surveying instruments, and Rittenhouse's instruments were eagerly sought by surveyors and men of science as the finest available in America. The volume of his work required that at various times he employ shop assistants, including his brother Benjamin. Rittenhouse also made at least one variation compass and numerous plain surveying compasses and levels. Often cited as the inventor of the vernier surveying compass, he was among the very first to make them from about 1770. Featuring a nonius or vernier scale that enabled the surveyor to compensate for the angular difference between true north and magnetic north, "Rittenhouse's improved compasses," as they were known, became the basic instrument specified by the government for surveys of national public lands and remained in official use until the mid-nineteenth century. In 1766 Rittenhouse married Eleanor Coulston; they had two children. Two years after her death during childbirth in 1770, he married Hannah Jacobs; they had one child, who died in infancy.

For part of the year 1774, Rittenhouse held the post of city surveyor of Philadelphia, and throughout his career he served on commissions engaged in boundary surveys. These included surveys of portions of the boundaries of Pennsylvania with Maryland, New York, and what became the Northwest Territory as well as portions of New York's boundaries with New Jersey and Massachusetts. In 1784 he assisted in surveying a ninety-mile westward extension of the Mason-Dixon line, and in late 1772 or early 1773 he set the southwest corner of Pennsylvania, a point from which a line was run north in 1785 to establish the Pennsylvania-Virginia boundary. Experienced in common or terrestrial surveying, he also undertook topographical surveys of canals and rivers and was skilled in the use of astronomical observations for surveying.

Although Rittenhouse worked primarily as a maker of clocks and mathematical instruments, his major contributions to the sciences were in astronomy, for which his early studies of mathematics and the physical sciences served him well. He became closely involved with the transit of Venus in 1769, a scientific event of worldwide importance. Based on the preliminary calculations Rittenhouse had provided in 1768, the American Philosophical Society made elaborate plans to observe the event from three sites. For the occasion Rittenhouse constructed an observatory at his home in Norriton to serve as one of the sites, and he made most of the instruments used by himself and other observers at the Norriton observatory. These included a transit and equal altitude instrument, a regulator clock, and a transit instrument, which may have been the first telescope made in America. He also assisted in assembling the instruments for the other sites. Both Nevil Maskelyne, the British Astronomer Royal, and later Simon Newcomb, superintendent of the American Ephemeris and Nautical Almanac (authorized by Congress in 1849), attested to the accuracy of the observations of the transit made by Rittenhouse and his associates.

In 1770 Rittenhouse moved permanently to Philadelphia, where he constructed another observatory from which he regularly conducted observations. He maintained detailed records and published data on transits of Mercury and the satellites of Jupiter. He made observations of Uranus following its discovery, and of various solar and lunar eclipses, and calculations on meteors, comets, and other celestial phenomena. By this time his work as an astronomer had become recognized overseas, and in his Traité d'astronomie (1764) Jérome Le Français de Lalande noted that Rittenhouse's was the only American observatory of which he had knowledge. In 1770 Rittenhouse published "An Easy Method for Deducing the True Time of the Sun's Passing the Meridian" (Transactions of the American Philosophical Association 1 [1771]: 47-49), which the noted German astronomer Baron Franz Xaver von Zach included as part of his Tabulae Motuum Solis in 1792. Among Rittenhouse's important published works was a paper that provided his original solution for locating the place of a planet in its orbit, and he also published on the subjects of meteorology and geology and on the concept of magnetic dipoles.

Rittenhouse solved various problems in mathematics, producing the first of his mathematical papers in 1792, in which he sought to determine the period of a pendulum. He experimented with magnetism and electricity and in about 1784 produced the Rittenhouse Stove, an improvement on Benjamin Franklin's Pennsylvania fireplace.

Among Rittenhouse's best-known achievements was the construction of two orreries of his own design. Familiar with published descriptions and illustrations of orreries produced by several English makers, he based his design on John Rowning's Compendious System of Natural Philosophy (1758) and completed the instrument in early 1771. Although originally intended for the College of Philadelphia (now the University of Pennsylvania), it was purchased by the College of New Jersey (now Princeton University). In the summer of 1771 Rittenhouse built a second orrery on the same principle; it was purchased by the Pennsylvania General Assembly for the College of Philadelphia.

Thomas Jefferson, who saw the latter instrument during his sojourns in Philadelphia in 1775 and 1776 as a delegate from Virginia to the Continental Congress, was so intrigued with it that in 1783 he initiated a proposal to have it renamed "Rittenhouse" and to commission a similar instrument to be made for King Louis XVI of France, partly as an expression of gratitude for France's support during the American Revolution but primarily as evidence of American ingenuity. Rittenhouse agreed to make a third instrument, but poor health and other priorities interfered, and the project was abandoned.

Between 1773 and 1780 Rittenhouse calculated ephemerides for a number of almanacs published in Virginia, Pennsylvania, and Maryland. During this period he was in charge of the State House clock and of the scientific instruments and apparatus of the College of Philadelphia, and he served as librarian of the American Philosophical Society. In 1775 he delivered the society's annual address. The society's plans to erect a public astronomical observatory with Rittenhouse as its director had been submitted to the state legislature just as the American Revolution erupted, which caused its postponement and eventually its cancellation.

As one of the most prominent mechanicians of his time, Rittenhouse became involved at the outset of the Revolution with a variety of military responsibilities. He served as an engineer with the Committee of Safety in 1775, as its vice president in 1776, and as its president in 1777. He supervised the local casting of cannon and the manufacture of saltpeter, and he arranged for the substitution of iron for lead weights in clocks throughout the city to provide lead for making ammunition. He selected sites for a gunpowder mill and a magazine for military stores, supervised production of chains for protecting the Philadelphia harbor, and experimented with rifling of cannon and musket balls. During this period he was also a member of the Pennsylvania General Assembly and of the state constitutional convention of 1776. He served as a member of the Board of War, a trustee of the Loan Fund, and from 1779 to 1787 was the state treasurer.

From 1779 to 1796 Rittenhouse served as a member of the Board of Trustees of the University of Pennsylvania, where he held the position of professor of astronomy in 1780-1781. He was a member of the committee to organize the United States Bank, and in 1792 President George Washington appointed him the first director of the newly established U.S. Mint, a position he held until 1795.

Among the first elected to membership in the American Philosophical Society in 1768, Rittenhouse was active from the time of its founding, having served as curator, librarian, secretary, vice president, and as a member of many of its committees, and he contributed numerous articles to its publications. In 1791 he was elected the second president of the society, succeeding Benjamin Franklin on the latter's death. He received many honors, including three master of arts degrees; a privately owned ship was named for him; and in 1795 he was appointed a foreign member of the Royal Society of London.

Rittenhouse, who suffered poor health constantly throughout his lifetime, died at his home in Philadelphia. His body was laid beneath the floor of his observatory, the place later marked with a marble slab inscribed only with his name, age, and date of death. (His remains were later moved to a local cemetery.) Next to Franklin, Rittenhouse was the leading figure in eighteenth-century American science. His achievements reflect an unusual combination of theory and practice: while his major contributions were primarily observational and experimental, his name has become synonymous with precision instrumentation.

The collections of the American Philosophical Society contain three of Rittenhouse's manuscript notebooks, and other Rittenhouse papers are in the society's minutes, archives, and miscellaneous manuscripts. Letters, receipts, and orders are scattered in the collections of the Historical Society of Pennsylvania, primarily among the Benjamin Smith Barton Papers. The University of Pennsylvania Archives contain minutes of its board of trustees for the period during which Rittenhouse served and other related materials. Papers relating to the various Pennsylvania state committees and the Treasury on which Rittenhouse served are part of the state archives of the Pennsylvania Historical and Museum Commission in Harrisburg. Other Rittenhouse items are among the papers of Thomas Jefferson in the Manuscripts Division of The Library of Congress. All of Rittenhouse's papers on astronomy, the physical sciences, and mathematics were published in the first four volumes of the Transactions of the American Philosophical Society. The most important of these are "Projection of the Ensuing Transit of Venus," 1 (1771): 4; "Calculation of the Transit of Venus Over the Sun as It Happened June 3rd, 1769 in Lat. 40 N. Long 5h. West from Greenwich," "Apparent Time of the Contacts of the Limbs of the Sun and Venus; with other Circumstances of Most Note, in the Different European Observations of the Transit, June 3rd, 1769," "Delineation of the Transit of Venus," 1 (1771): 4-38; "New Method of Placing a Meridian Mark," 1 (1771): 181-83; "A Description of a New Orrery," 1 (1771): 1-3; "An Account of Some Experiments in Magnetism," 2 (1786): 178-81; "A Method of Finding the Sum of the Several Powers of the Sines," 3 (1793): 155-56; and "To Determine the True Place of a Planet," 4 (1799): 21-26. His writings on natural history appeared in the Columbian Magazine 1 (1786-1787), and an article coauthored with Francis Hopkinson on electricity was published in the Philadelphia Medical and Physical Journal 1, pt. 2 (1805): 96-160.

Rittenhouse's Memoirs of the Life of David Rittenhouse, LL.D., F.R.S., Late President of the American Philosophical Society, &c., Interspersed with Various Notices of Many Distinguished Men: With an Appendix Containing Sundry Philosophical and Other Papers, Most of Which Have Not Hitherto Been Published (1813), remains one of the most useful sources about his life and work. Also useful is Benjamin Rush, An Eulogium Intended to Perpetuate Rittenhouse Delivered . . . on the 17th Dec. 1796 (1797). The most recent biography, Brooke Hindle, David Rittenhouse (1964), emphasizes Rittenhouse's scientific activities and achievements. See also Hindle, The Pursuit of Science in Revolutionary America 1735-1785 (1956). A comprehensive family history, although containing errors, is provided by Daniel K. Cassel, A Genea-Biographical History of the Rittenhouse Family and All Its Branches in America. With Sketches of Their Descendants . . . (2 vols., 1893). Articles that relate to specific scientific achievements include Thomas D. Cope, "The Rittenhouse Diffraction Grating," Journal of the Franklin Institute 214 (July 1932): 99-104; Simon Newcomb, "Discussion of Observations of the Transits of Venus in 1761 and 1769," Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac, vol. 2 (1891), pp. 259-405; and W. Carl Rufus, "David Rittenhouse as a Mathematical Disciple of Newton," Scripta Mathematica 8 (Dec. 1941): 228-31.