In 1842-1855 he was pastor of the South Congregational Church of Boston, and in 1855-1860 was preacher to the university and Plummer professor of Christian Morals at Harvard; he then left the Unitarian Church, with which his father had been connected as a clergyman at Hadley, resigned his professorship and became pastor of the newly established Emmanuel Church of Boston.
In 1796 he was made a member of the Institute, was appointed to a professorship of political economy, and founded tin Journal d'economie publique, de morale et de legislation.
On the outbreak of the Franco-German War he resigned his professorship and acted for a time as correspondent to The Times in Italy.
His eldest son, Eilhard Ernst Gustav, born at Berlin on the 1st of August 1852, became professor of physics at Erlangen in 1886, and his younger son, Alfred, born at Berlin on the 18th of July 1856, was appointed to the extraordinary professorship of Egyptology at Bonn in 1892.
After two years he returned to Copenhagen, but his lectures excited so much disapproval that he took a professorship at Halle in 1804.
He became famous as a teacher of Greek letters and the Platonic philosophy; in 1463 he was made professor at Padua, and in 1479 he was summoned by Lorenzo de' Medici to Florence to fill the professorship vacated by John Argyropoulos.
In 1905 he held the professorship of physics in the Royal Institution, London, in addition to his Cambridge professorship. He was knighted in 1908 and awarded the O.M.
Degree at Cambridge, preaching on that occasion a sermon which induced John Norris (1734-1777) to found the Norrisian professorship of divinity.
On his return to Naples he found himself out of touch with the prevailing Cartesianism, and lived quietly until in 1697 he gained the professorship of rhetoric at the university, with a scanty stipend of loo scudi.
In 1849 he was appointed professor of practical chemistry at University College, London, and from 1855 until his retirement in 1887 he also held the professorship of chemistry.