Brief Biographies from the Jackson/Van Buren Era (A):

Abbott, Charles Jeffrey 1806 - ?


Abbot, Gorham Dummer 1807 - 1874:

Minister and educator.  Attended Bowdoin, graduating in 1826, then spent some time at Andover Theological Seminary but did not graduate.  Served as a pastor in New Rochelle, NY from 1837-41.

Having helped Jacob conduct the Mount Vernon School for girls in Boston from 1831-33, he took up the cause of girls education again with the establishment of a girls' school in New York (known as Abbott's Institution and by other names), begun in 1843, in which he was helped by Jacob, John, and Charles.  This became his most siginificant life work After this school, he began the Springler Institute which he conducted until 1870.  Its catalogue stated its aim was "to provide for daughters, priveleges of education equal to those of sons in our Universities, ..."

His brothers included Jacob and John S.C. Abbott (despite their spelling their names differently). Their father, Jacob Abbot 2nd moved from Concord NH to become a pioneer in developing southern Maine, and establish a family home in Hallowell, Maine.

Abbott, Jacob 1803-1879:

b.11/14,d.10/31Born in Hallowell, Maine; Bowdoin College 1820; Andover Theological Seminary 1825. Was professor of mathematics and natural philosophy at Amherst College from 1825-9. Ordained Sep. 18, 1834 at Elliot Church, Boston Highlands; was succeeded by his brother, Rev. J.S.C., on Nov. 25, 1835.

Wrote copiously for juveniles, including his first success, The Young Christian: Or, a Familiar Illustration of the Principles of Christian Duty (1825), The Corner Stone, 30 volumes of juvenile biographies, 24 volumes of the "Rollo", "Lucy", and "Jonas" stories.

"Abbott" was originally spelled with one "t", but Jacob and (most of?) his brothers added another "t"  (Gorman Dummer did not).

Another brother was John Stevens Cabot Abbott.

source: DAB.

Abbott, John Stevens Cabot 1805 - 1877

Congregational minister and historian, and active in women's education.
Graduated Bowdoin in 1825, a classmate of Hawthorne and Longfellow; served a year as principal of the academy at Amherst MA; studied at Andover Seminary, graduating in 1829, and was ordained to a pastorate at Central Calvinistic Church in Worcester, MA on 1/28/1830 (served until 1834). He served from 1835-41 at Eliot Congregational Church in Roxbury, and from 1841-43 at First Congregational Church in Nantucket.

He began to write with The Mother at Home in 1834; in 1843, got involved in the seminary for young ladies in New York (known as Abbott's Institution and by other names), which was started by his brother, Gorham D. Abbot, with help of brothers Jacob and Charles.  He mainly worked for this school until 1843, when he returned to Brunswick, ME, where his son attended Bowdoin and he conducted historical research using the college library.

His History of Napoleon Bonaparte, serialized in the new Harper's Magazine from 1851-54, and published in 1855, was a huge success (and very helpful to Harper's), and he continued to write much, mostly on historical subjects.  He was a popularizer who tended towards praising his subjects extravagently (including Napoleon).

In 1861 he returned to the ministry, serving at Howe Street Church, New Haven, CT for 5 years, and later at Second Church in Fair Haven CT from 1870-74 (and in between?).

"Abbott" was originally spelled with one "t", but Jacob and (most of?) his brothers added another "t"  (Gorman Dummer did not).

source: DAB

Adair, James 1709-1783:

Irish-American Pioneer who lived among the Chickasaw Indians between 1735 and 1775, and wrote History of the American Indians (1775) which theorized that the Indians were descended from ancient Jews.

Adams, Abigail 1744-1818:

Wife of John Adams. Tried to pursuade him to consider equal rights for women at the time the constitution was drafted.

Adams, Charles Francis 1807-1886:

Lawyer, diplomat and writer. He played an important role in keeping Great Britain from going too far in their friendliness towards the Confederacy during the Civil War. Published early versions of the copious Adams family correspondence.

The only son of John Quincy Adams who made a successful career. His older brothers, George Washington Adams was an apparent suicide. Both George and John Adams Jr. seemed to suffer greatly from pressure to live up to a great family name.

Married the daughter of Peter Brooks, perhaps the richest man in Massachusetts.

Adams, George Washington 1801 - 1829:

Adams, Hannah 1755 - 1831:

Author of a Dictionary of Religions. Born Medford, MA.

Adams, John 1735-1826:

Second president of the U.S. Signer of the Declaration of Independence. He had a distinguished career in diplomacy between 1777 and 1788, then served two terms as Vice President, and one as President.

He tried to suppress "seditious" speech in order to control the passions set loose in the U.S. by the French Revolution. This created such a strong reaction as to sweep in the Jeffersonian Democrats in 1800, making Adams the only 1 term president among the first six presidents.

Adams, John, Jr. 1803 - 1834:

2nd son of John Quincy Adams. He was expelled from Harvard in the "Great Rebellion of 1823". His father tried to set him up in a flour mill in Washington, but he drank excessively, and this probably contributed to his early death.

Source: Shepherd, Cannibals of the Heart.

Adams, John Quincy (1767 - 1848):

Son of John Adams, John Quincy's formative years were partly spent in Europe, where his father served as a diplomat.

U.S. Senator from 1803-1808, and Minister to Russia from 1809-11. Declined an appointment to the Supreme Court in 1811. He was a rare creature in New England during the years before the war of 1812 - a Republican, in favor of the war with Britain, and in favor of New England's fully backing the war, despite the economic suffering it caused there. With Henry Clay, helped negotiate the Peace of Ghent which concluded the war.

Under James Monroe, he served as Secretary of state, and did much to develop the Monroe Doctrine towards Latin America.

From 1825-1829 he was President of the U.S.

Remarkably, after his presidency, he accepted election to the House of Representatives where he served until his death. He was somewhat caught up in the Anti-Masonic movement, which expressed revulsion against the organization's secrecy and status as a fraternity of powerful men.

He became something of an anti-slavery hero by protesting year after year the "gag rule" which prohibited discussion of any anti-slavery measure in the House, until this House rule was finally abolished. He stayed in harness literally til the end of his life, when he fell stricken on the floor of the House of Representatives.

Adams, Louisa Catherine Johnson 1775 - 1852:

b. Feb. 12, 1775, d. May 15, 1852
Wife of John Quincy Adams. (more to be added later).

Source: Shepherd, Cannibals of the Heart, Notable American Women

Adlum, John 1759-1836:

Produced the Catawba grape for wine making. Wrote Adlum on Making Wine in 1826, and was a pioneer in his field.

Born York, PA.

Agassiz, Louis 1807- 1873:

A Swiss born naturalist who became a professor at Harvard from 1848-73. Some of his work had to do with explaining the action of glaciers. His second wife, formerly Elizabeth Cabot Cary (1822 - 1907) was a founder of Ratcliff College and its president from 1894-1902.

Agate, Frederick Styles 1803-1844:

Painter, Born in Sparta NY. Helped create the American Academy of Design in 1826.

Agnew, David Hayes 1818-1892:

Surgeon, educator, and author of books on surgury. Born Lancaster Co., PA.

Aiken, George L. 1830-1876:

Actor and playwright, born in Boston. Made Uncle Tom's Cabin into a play in 1852.

Akerman, Amos Tappan 1821-1880:

Lawyer born in Portsmouth, NH. Practiced in Georgia, served in the Confederate Army, became U.S. Attorney general 1870-71.

Akers, Benjamin Paul 1824-1861:

Sculptor of Una and the Lion and The Dead Pearl Diver. Born in Sccarappa Maine, which is now part of Westbrook.

Alaman, Lucas 1792 - 1853:

Mexican historian who held offices under Santa Anna. Anti-democratic, he has been held responsible for much of the hostility between the U.S. and Mexico which helped bring about the Mexican-American war. Wrote some valuable works on Mexican history.

Alcott, Amos Bronson (1799-1888):

Bronson, as he was called, was deeply religious in a mystical way; his first calling was to awaken the innate abilities, goodness, and religious comprehension of children. He seemed to have a magical effect on people, though he often seemed hapless and not cut out for this world. Emerson lovingly called him a "tedious archangel". Another said "one cannot laugh at him without loving him".

One of Alcott's earliest friends (from about 1827), the Untarian reformer Samuel J. May, described him: (Shepard, Pedlar's Progress, p106)

What he wrote in his notebook in 1828(?) could have served as the coda of the Transcendentalist movement among Harvard-educated Unitarian ministers, and particularly to express what he was driving at in the Temple School:  (Shepard, Pedlar's Progress, p126) And Elizabeth Palmer Peabody, a great educational reformer in her own right, and not overly humble, wrote to him: A poor New England Farm boy from Wolcott, CT with little education, he began his career as a peddler in the south, and there, where educational benchmarks were lower, began to try his hand as a teacher. From 1823-39, he taught school in Connecticut, Boston, and Pennsylvania. In Boston, in 1834 began an ambitious and unusual teaching enterprise, and fell in with Emerson's crowd.

The school he started in 1834, housed in a Masonic Temple was called the "Temple School".  There he taught small children, with the assistance of Elizabeth Peabody and the brilliant Margaret Fuller. He stimulated the children to think for themselves, and conducted Socratic dialogues with them about religion and ethics. He believed, and was anxious to prove, that children carried their own internal "book of life"; that they needed just a bit of gentle coaxing to become aware of their inner goodness and natural knowlege.

He had a gift for his original mode of teaching, in an age when rote learning was the norm. In 1836 and '37, he published Record of Conversations on the Gospel, the "conversations" being between him and the children he taught. Some very good excerpts can be found in Perry Miller's invaluable The Transcendentalists: An Anthology. The book, however, involved him in scandal, and he was attacked by the Boston newspapers. An example of what was "scandalous" in the book (quoted in Boller, American Transcendentalism...), is:

Between the "scandalousness" of his writing and interacting with children, his way of drawing religion out of children rather than impressing them with external authority, and finally his admission of an African American girl to the school, he outraged his students' parents, and so the school had to be closed.

In 1844 he started a commune - of only a handful of people, called Fruitlands. Most of the colonists had their heads in the clouds - according to Boller, Alcott's wife did all the work, and the diet consisted mostly of cornmeal mush. The colony lasted but a very few months.

Alcott lived another 44 years, sometimes writing (including a biography of Emerson), sometimes lecturing for a fee as many did in his day, or leading discussion groups. It was a precarious living until his daughter, Louisa May Alcott (author of Little Women) became a successful writer.

 (Main source: Shepard, Pedlar's Progress)

Alexander, John Henry 1812-1867:

Scientist born in Annapolis, MD. Writer, and proponent of standardized weights and measures.

Alexander, Stephen 1806-1883:

Astronomer born Schenectady NY. One of the original 50 members of the National Academy of Sciences.

Alfieri, Cesare 1796-1869:

Proponent of Italian unification.

Allen, Elisha Hunt 1804-1883:

Practice law in Bangor Maine, and was a member of the House of Representatives. Consul at Hawaii 1850-56, and later served there as minister of finance; chancellor and chief justice; Hawaiin minister to the U.S. from 1876-83.

Allen, Ethan 1738-1789:

Revolutionary War hero. seized Fort Ticonderoga with Benedict Arnold in 1775. Prisoner of the British from 1875 - 78, and one of the few captured with him to survive.

A religious freethinker, he was ironically born in Litchfield, Connecticut, home of the famous ministries of Jonathan Edwards and Lyman Beecher.

Allen, Henry Watkins 1820-1866:

The son of a doctor; refused to enter business as his father wanted, entered college, then dropped out, and became a lawyer.
In 1842, he joined the army in Texas (then an independant nation), under Houston.  He married against the will of his wife's family, which led to a duel in which he was seriously injured, but the families were reconciled later.

In 1854(?) he saied to Europe to fight for Italian independence.  He was too late to be of any help there, but stayed and toured Europe for a while.  His Adventures of a Sugar Planter (1861) describes this experience.

After Europe he became active in politics.  His main achievements came with the Civil War, where he signed up as a private, quickly rose to Lieutenant-colonel, and then Brigadier general.  After taking some very serious wounds, he left the military and became governor of his native (since around 1850) Louisiana.  Though half of Louisiana was ceded to the Union, he brought the part west of the Mississippi back from eminent collapse.  He lived his last year in Mexico; his death was probably due to the ruination of his health by his wounds, especially the leg wound for which doctors wanted to amputate.
SOURCE: DAB; see also Henry Watkins Allen of Louisiana.

Allen, John 1810-1892:

Invented modern dentures, with porcelain teeth attached to a platinum plate, for which he received patent in 1851. Born in Broome County NY.

Allen, John (of Tennessee)

"a peripatetic lawyer, filibusterer, and land speculator" (p105, Da Bruhl)

"Well to do planter and close friend of Andrew Jackson." His plantation, Allenwood, on the Cumberland River near Gallatin, was often visited by Jackson.

Brother of the congressman Robert Allen, and father-in-law of Sam Houston (see 1/22/29 -- the marriage was catastrophic and the two essentially never lived together).

(Source: mostly Da Bruhl, Sword of San Jacinto, p96ff)

Allen, Joseph Henry 1820 - 1898:

 Unitarian minister, teacher and writer. Wrote Our Liberal Movement in Theology (1882), Christian History in Its Three Great Periods (1883), and Historical sketch of the Unitarian Movement (1894). He also authored, in the late 1860s, a widely used school series of Latin manuals.

He was born in Northboro, MA.  His father was the minister of the First Church there for 56 years; his mother was a daughter of Henry Ware, who made Harvard a stronghold of Unitarian theology beginning in 1805.

In 1847, he became pastor of the Washington DC Unitarian church; in 1850, his ministry moved to Bangor, ME.  From 1857, he was mostly a teacher and writer.  He was associate editor of the Christian Examiner from 1863-65, and was lecturer on ecclesiastical history at Harvard from 1887-1891.

Allen, Richard 1760 - 1831:

One of the founders of the African Methodist Episcopal Church, and its bishop from 1816-31. Born a slave in Philadelphia.

Allen, Richard (Irish abolitionist) ? - ?:

Correspondent in Dublin, of Wm. Lloyd Garrison. Worked with James Haughton. In the summer 1841 helped American abolitionists tour Ireland, and helped draw up an Irish anti-slavery petition.

Source: p9, 14, Ignatiev, How the Irish Became White.

Allen, Robert 1788 - 1844:


Congressman from Tennessee 1819-27. Formerly Colonel under Andrew Jackson in the War of 1812.

Lived in Carthage TN from 1804, where he practiced law, and later farmed and engaged in business.

Brother of John Allen; he introduced Sam Houston to the family when both men were in Congress. This led to Houston's unfortunate marriage to John's daughter Eliza.

(Source: Da Bruhl, Sword of San Jacinto, p96; Biog. Dir of Am. Congress.)

Allen, William 1784-1868:

Congregational minister. Born Pittsfield MA. Grad Harvard in 1802. President of Dartmouth from 1817-19 and Bowdoin from 1819-31 and 33-38. Compiled American Biographical and Historical Dictionary, initially in

Allen, Zachariah 1795-1882:

Invented the first hot-air house-heating system 1819), and an automatic steam-engine cutoff (1834).

Born in Providence RI.

Allibone, Samuel Austin 1816-1889:

Editor and librarian. Compiled A Critical Dictionar of English Literature and British and American Authors between 1858 and 1871.

Born in Philadelphia.

Allston, Washington 1779-1843:

Artist, poet and novelist, born in Waccamaw, SC. Studied in Europe.

ALSTON, Willis, 1769-1837

ALSTON, Willis, (nephew of Nathaniel Macon), a Representative from North Carolina; born near Littleton, Halifax County, N.C., in 1769; completed preparatory studies and attended Princeton College; engaged in agricultural pursuits; member of the State house of commons 1790-1792; served in the State senate 1794-1796; elected as a Republican to the Sixth and to the seven succeeding Congresses (March 4, 1799-March 3, 1815); chairman, Committee on Revisal and Unfinished Business (Thirteenth Congress); again a member of the State house of commons 1820-1824; elected to the Nineteenth and Twentieth Congresses and reelected as a Jacksonian to the Twenty-first Congress (March 4, 1825-March 3, 1831); chairman, Committee on Elections (Twenty-first Congress); was not a candidate for reelection to the Twenty-second Congress; resumed agricultural pursuits; died in Halifax, N.C., April 10, 1837; interment in a private burying ground on his plantation home, ?Butterwood,? near Littleton, Halifax County, N.C.

Source: Biog. Dir. of Am. Congress.

Alter, David 1807-1881:

Physicist and Physician, born in Westmoreland Co., PA. Made discoveries which made spectral analysis of chemicals possible.

Alvarado, Juan Bautista 1809-1882:

Governor of the virtually independent Department of California from 1836 - 41, when it was part of Mexico.

Alvarez, Juan 1790? - 1867:

Mexican general of Indian descent who helped Santa Anna seize power in 1823, fought with Santa Anna against the U.S. in 1846-7. He helped overthrow Santa Anna in 1855 and was acting president for two months at the end of that year.

Ames, David and John

Owners of the Ames Paper Mill in Springfield, MA, an advanced facility for the day.

Information should be found in Chapin, Sketches ... Old Springfield

Ames, Oakes 1804-1873:

Financier and politician. Born in Easton Mass. Made a fortune in Oliver Ames and Sons, shovel manufacturers. Served in House of Representatives 1863-73.

Ames, Oliver 1807 - 1877:

Headed a very successful shovel manufacturing enterprise, Oliver Ames and Sons, and during and after the Civil War, a successful railroad man.

Ampere, Andre Marie 1775 - 1836:

Made some of the most important discoveries in the fields of electicity and magnetism (French).

Anderson, Alexander 1775 - 1870:

American engraver born in New York. Made first wood engravings in America.

Anderson, John 1792-1853:

Representative from Maine; born in Windham, Maine, July 30, 1792; attended the common schools; was graduated from Bowdoin College, Brunswick, Maine, in 1813; studied law; was admitted to the bar in 1816 and commenced practice in Portland, Maine; member of the State senate in 1823; elected to the Nineteenth and Twentieth Congresses and elected as a Jacksonian to the Twenty-first and Twenty-second Congresses (March 4, 1825-March 3, 1833); chairman, Committee on Elections (Twentieth Congress), Committee on Naval Affairs (Twenty-second Congress); was not a candidate for renomination in 1832; mayor of Portland 1833-1836 and again in 1842; United States attorney for the district of Maine 1833-1836; collector of customs for the port of Portland 1837-1841 and 1843-1848; resumed the practice of law; died in Portland, Maine, August 21, 1853; interment in Town Cemetery (then a part of the farm of his ancestors) on River Road, Windham, Maine.
Above from Biog Dir. of Congress.

Anderson, Joseph 1757 - 1837:

Born in White Marsh PA. Senator from Tennessee from 1797-1815. First comptroller of the Treasury from 1815-36.

Anderson, Richard H. 1821-1879:

West point grad. Rose to major general of the Confederate Army.

Anderson, Robert 1805 - 1871:

Born in Kentucky; grad West Point in 1825. Commanded Fort Sumter in Charleston, SC when the confederate forces attached it. He is supposed to have mustered in Abraham Lincoln (Thomas, p 33) when the latter served as militia captain in the Black Hawk War.

Andrew, James Osgood 1794 - 1871:

Methodist Episcopal Bishop. Born in Wilkes County GA. His holding of slaves helped split the church, and he was one of the first bishops of the Methodist Episcopal Church, South (1846).

Andrews, Ethan Allen 1787 - 1858:

Born New Britain, CT. Translated a Freund's Latin-German lexicon into a Latin-English lexicon in 1850, which became the original of Harper's Latin Dictionary.

Andrews, Lorrin 1795 - 1868:

Missionary in Hawaii from 1828 - 41. First associate justice of supreme court in Hawaii 1852-55. Born in East Windsor (now Vernon), CT.

Andrews, William Draper 1818 - 1896:

Inventor of a centrifugal pump.

Angell, Joseph Kinnicutt 1794-1857:

Lawyer and author of legal treatises. Born in Providence RI.

Anthon, Charles 1797 - 1867:

Classical scholar born in New York City. Professor at Columbia from 1820 to 1867. Edited texts and classical dictionaries.

Applegath, Augustus 1788 - 1849:

Invented a vertical printing press in England.

Appleton, Daniel 1785 - 1849:

Publisher and founder of D. Appleton & Co., book publishers, in 1838 (bought the building that housed the Old Corner bookstore in Boston, and made it home of his printing company).

Appleton, Nathan 1779 - 1861:

Pioneered cotton cloth manufacture in Waltham, Lowell, and Lawrence MA, and Manchester, NH. One of the cofounders of Lowell, MA.

Appleton, Thomas Gold 1812 - 1884

Genial poet and essayist; son of Nathan Appleton.

Arago, Francois 1786-1853:

French physicist important to the discovery of principals concerning light and magnetism. Took part in the July Revolution in 1830. Responsible for abolition of slavery in the French colonies.

Archer, Branch Tanner 1790 - 1856:

Born in Virginia. Moved to Texas in 1831. Active in Texas independence movement. Texas secretary of war under President Lamar.

Arguello, Luis Antonio 1784-1830:

Governor of California under Mexican rule from 1822-25. Led expedition to Columbia River region in 1821.

Arminius, Jacobus 1560 - 1609:

Dutch Reform theologian, whose name (Arminianism) stands for a rejection of the Calvinist doctrine of predestination, a doctrine which played an important role in the history of the American Churches.

Armistead, Lewis Addison 1817-1863:

Born in New Bern, NC. Was a Brigadier General killed in Pickett's charge at Gettysburg. An army officer from 1839 til his death.

Armstrong, John 1758 - 1843:

Secretary of War in the war of 1812, and held largely responsible for American failures in that war.

Armstrong, William George 1810-1900:

An English baron who invented a hydroelectric generator (1840-5), a hydraulic crane, and the prototype (around 1855) of all modern breech-loading artilery.

Arnold, Samuel Green 1821 - 1880:

Lieutenant gov. of Rhode Island (born in Providence) in 1852, 61, and 62; U.S. Senator from 62-63; and historian of Rhode Island.

Arthur, Timothy Shay 1809 - 1885:

Born in Newburgh, NY, he was a writer and temperance crusader; author of the extremely popular Ten Nights in a Barroom and What I Saw There.

Asbury, Francis (Aug 26, 1745 - Mar. 31, 1816):

First(?)Methodist bishop in America. At age 23 he became an itinerant preacher under the guidance of John Wesley. Sent as missionary from England in 1771, he was recalled in

Ashley, William Henry 1778 - 1838:

Fur trader and explorer. Traveled nearly as far as the Great South Lake.

Ashmead, Isaac 1790-1870:

Founder in 1819 of the Sunday and Adult School Union; later called the American Sunday School Union. Born in Germantown PA.

Aspinwall, William Henry 1807 - 1875:

Promoter of the Pacific Mail Steamship Co. and Panama Railroad (1850-55). Born in New York City.

Astor, John Jacob 1763 - 1848:

Immensely successful German-American fur trader. Monopolized Mississippi Valley fur trade by 1817, and the upper Missouri in 1822-34. Made large and profitable loans to the U.S. in the war of 1812, and invested heavily in New York real estate.

Atkinson, Edward 1817 - 1905:

Textile manufacturer and economist. Born in Brookline, MA.

Atkinson, Thomas 1807 - 1881:

Episcopalian bishop of North Carolina. Helped reunite northern and southern branches of the church after the civil war. Born in Dinwiddie County VA.

Attwood, Thomas 1783 - 1856:

Chartist and english reformer. Organized the Political Union in 1830, and was member of Parliament from 1832-9.

Atwater, Caleb 1778 - 1867:

Pioneer in Chilicothe, OH, amateur naturalist, esp. in archeology. Sent on May 1829 to help negotiate a treaty with the Winnebago and other Indians who met at Prairie du Chien. His book, Remarks Made on a Tour to Prairie du Chein, thence to Washington City in 1829 (orig: Columbus, OH, 1831) described the landscape, towns visited along the way, the Indians and their customs, as well as Philadelphia and Washington, which he visited at the end of the trip. (Source: DAB, and Atwater, Remarks)

Audubon, John J. 1785-1851:

Born in Haiti, he became famous in America for his observations and beautiful, meticulous paintings of the birds of America. He began this career after failing as a merchant in 1819. After years of traveling in the wilderness, and more years of struggle for recognition for what he had done, he settled in New York City, and built up an estate from 1841-51.

Austin, Stephen F. 1793 - 1836:

One of the earliest American settlers in Texas. He organized a colony from 1822-32 of Americans who, to become Mexican citizens were (nominally at least) converted to Catholicism.

Austin, William 1778 - 1841:

Lawyer and writer of Peter Rugg, the Missing Man (1824). Born in Lunenburg Mass.

Auzoux, Louis 1797 - 1880:

French inventor of a paste which made possible the casting of anatomical models; popularized the study of anatomy.

Avogadro, Amedeo 1776 - 1856:

Important Italian chemist and physicist who theorized that equal volumes of any gas at a given temperature and pressure have equal numbers of molecules (Avogadro's number).