Smith, Robert

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(b. Lea, near Gainsborough, England, 1689; d. Cambridge, England, 2 February 1768)


Smith’s father, John Smith, was rector of the parish of Lea: his mother, Hannah Smith, was the aunt of Roger Cotes, Plumian professor of astronomy at Cambridge. Smith was educated at the Leicester Grammar School and from 1708 at Trainity College, Cambridge, where he lived with and assisted his cousin Coles, Smith graduated B.A. in 171 I and M.A. in 1715. He was elected a fellow of his college in 1714, Plumian professor in 1716, and fellow of the Royal Society in 1718, He received the LL.D. in 1723 and the D.D. in 1739, Appointed master of Trinity College in 1742, Smith was vice-chancellor of the University in 1742–1743, and he held the Plumian professorship until 1760. Among his many bequests to the university and to his college, he founded the two Smith’as prizes for undergraduate attainment in mathematics and antrural philosophy.

Smith wrote on optics and harmonics. In 1738 he published A Compleat System of Optics in Four Books, viz. A Popular, at Mathematical, a Mechanical, and a Philosophical Treatise. Both comprehensive and reliable, the work became probably the most influential optical textbook of the eighteenth century. It was also published in Dutch in 1753, in German in 1755, and in two different French translations in 1767, In 1778 an abridged version was published in English. In turn, its popularity helped to establish the eighteenth-century conviction that light is particulate.

Although Newton had expressed some uncertainty about the nature of light, Smith asserted in the “Popular Treatise” that there was no reason to doubt that light consisted of material particles. He then gave a plausible explanation of most known optical phenomena in terms of particles of light that were acted upon by attractive and repulsive forces. In these explanations Smith never even suggested that any vibrating medium might exist to produce light or “Newton’s rings,” nor did he even mention Newton’s theory of “fits.” Rather he repleated Newton’s assertion that the rings were caused by the disposition of varying thicknesses of air or films that reflect or refract different colors of light.

In the “Mathematical Treatise,” Smith developed a very comprehensive set of geometric propositions for the computation of the focus, location, magnification, brightness, and aberrations of systems of lenses and mirrors. Apparently he was the first person to construct images by means of an unrefracted central ray and a ray parallel to the axis that is refracted through the focus.1 He also derived a particular case of the relationship now known as the Smith-Helmholtz formula or the theorem of Lagrange. Using a relationship between the magnification and location of object and image for one lens, Smith showed that the same relationship was invariant within a system of any combination of lenses.2

In the “Mechanical Treatise,” Smith gave methods for making optical instruments, and in the “Philosophical Treatise.” he gave an account of astronomical discoveries.

In 1749 Smith published Harmonics, or the Philosophy of Musical Sounds, which had a second edition in 1759 and a postscript in 1762. Although it was partly a textbook, Smith’s principal objective was to describe his system of tempering a musical scale by making “all the consonances ... as equally harmonious as possible...,”3 He derived the “equally harmonic” intervals by a mathematical theory and confirmed his results on an organ and a harpsichord. Smith’s temperament was an improvement on existing systems, but its use required impractical mechanical changes in the instruments.


1. Ernst Mach, The Principles of Physical Optics (New York, 1953). 57.

2. Smith credits Roger Cotes with the discovery of the relation ship for one lens. See Smith, A Compleat System, bk, II, ch. 5. esp. arts, 247–249, 261–263, 267. 465–474, See also Lord Rayleigh, “Notes, Chiefly Historical...,” in Philosophical Magazine, 5th ser., 21 (1886), 466–469

3. Smith, Harmonics (1749), p. vi.


I. Original Works. Smith’s works are A Compleat System of Opticks in Four Books, viz. A Popular, a Mathematical, a Mechanical and a Philosophical Treatise(Cambridge, 1738) and Harmonics, or the Philosophy of Musical Sounds (Cambridge, 1749; repr., New York. 1966).

II. Secondary Literature. There is no full biography of Smith. Biographical information in this article is from the Dictionary of National Biography, XVIII, 517–519. Smith is mentioned in Ernst Mach. The Principles of Physical Optics (New York, 1953), 57, 62. The most useful article on the Smith-Helmholtz formula is Lord Rayleigh, “Notes, Chiefly Historical, on Some Fundamental Propositions in Optics,” in Philosophical Magazine, 5th ser., 21 (1886), 466–476. The best discussion of Smith’s historical importance is in an unpublished master’s thesis by Henry John Steffens, “The Development of Newtonian Optics in England, 1738–1831” (Ithaca, New York: Cornell University, 1965). On Smith’s Harmonics, see Lloyd S. loyd, “Robert Smith,” in Grove’s Dictionary of Music and Musicians, 5th ed., VII (London, 1954), 857–858: and “Temperaments.” ibid., VIII , 377.

Edgar W. Morse

Smith, Robert

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Robert Smith was a lawyer and statesman who served as attorney general of the United States under President thomas jefferson and as secretary of state under President james madison.

Smith's father, John Smith, a native of Strabane, Ireland, immigrated to the American colonies in the 1740s. By 1759, he was living in Baltimore and had established himself as a merchant and shipping agent. In 1766, he financed the building of Baltimore's first market house and the development of the city's first residential neighborhood. He was an advocate of independence for the American colonies and active in politics and the military.

Smith was born in November 1757 in Lancaster, Pennsylvania. He came of age at the height of the American Revolution and, like his father and his brother, Samuel Smith, volunteered to serve. He distinguished himself at the Battle of Brandywine, but his experience convinced him that he was not suited to a military career.

After the war, Smith attended the College of New Jersey (later Princeton University). He graduated in 1781 and went on to study law. Following his admission to the bar, he established a practice in Baltimore, and looked after family business interests while his father served the first of two terms in the Maryland state senate.

By 1793, Smith had followed his father into the political arena. He served in the Maryland state senate from 1793 to 1796 and in the Maryland House of Delegates from 1796 to 1800. While in the house of delegates, he served a concurrent term on Baltimore's city council.

In 1801, Smith was appointed secretary of the Navy when his brother stepped down from that post following an appropriations dispute with Congress. Up to that time, military appropriations had not been monitored or controlled as closely as other government expenditures—and President Jefferson and members of his cabinet had become increasingly concerned about moneys drawn from the Treasury by the Secretaries

of War and the Navy. When the cabinet curtailed lump-sum payments and demanded an itemized accounting of how funds were spent, Smith's brother considered the demands to be a personal attack, and he resigned. Smith, who had a far better understanding of business and accounting practices, was less inclined to view the increased scrutiny as an attack on his character.

Most historians record that Smith served as secretary of the Navy from January 1802 to March 1805, but there are indications that he continued to act as secretary during his appointment as attorney general of the United States from March 1805 to the end of the year. Though his was an official appointment as attorney general, he argued no cases before the U.S. Supreme Court and wrote no opinions.

There are reasons to believe that Smith's cabinet service as secretary of the Navy and official duties as attorney general were curtailed for personal as well as political reasons. By 1805, his family had been involved in a number of incidents that caused embarrassment in Washington, D.C. One celebrated event covered by Washington papers was a party given by Smith and his wife for a niece who married Napoléon Bonaparte's brother. Elizabeth Patterson Bonaparte scandalized Washington with her transparent ball gown, and offended the British ambassador with her suggestive dancing.

In January 1806, Smith was asked by the president to consider an appointment as chancellor of Maryland and chief judge of the District of Baltimore. (Chancellor is the name given to the presiding judge of a court of chancery.) Smith declined the opportunity and remained in Washington.

By July 1806, Smith was once again acting as the secretary of the Navy. In United States v. Smith, 27 F. Cas. 1192 (D.N.Y. July 15, 1806), he was called to testify in this capacity as a material witness in a New York trial. And in United States v. Burr, 25 F. Cas. 55 (D. Va. Aug. 31, 1807), Smith, as secretary of the Navy, was asked to verify the authenticity of government documents ordering Aaron Burr's capture.

Smith was named secretary of state on March 6, 1811, by President Madison. He served until November 25, when Madison called for his resignation. Madison intimates regarded Smith as an "ornamental" secretary of state because Madison, who had been secretary of state in the Jefferson administration, continued to discharge the duties of his previous office while serving as president. Before calling for Smith's resignation, Madison attempted to ease him out of office by offering him an embassy post in Russia. Smith declined the offer and decided to return to Baltimore.

In 1813, Smith was appointed provost of the University of Maryland. For the next twenty years, he devoted his time to building the university's prestige and securing its financial future.

Smith died in Baltimore on November 26, 1842.

further readings

Armstrong, Thom M. 1991. Politics, Diplomacy, and Intrigue in the Early Republic: The Cabinet Career of Robert Smith, 1801–1811. Dubuque, Iowa: Kendall/Hunt.