I. Friedrich Heinrich, a German philosopher, born in Dusseldorf, Jan. 25, 1743, died in Munich, March 10, 1819. In his 18th year he was sent to Geneva to complete his mercantile apprenticeship, and during a residence there of three years studied mathematics, medicine, and philosophy. On his return to Dusseldorf he was placed at the head of his father's mercantile establishment, and soon after married; but in 1770 he renounced commerce, being appointed councillor of finance for the duchies of Berg and Julich. This office allowed him to indulge his tastes for literature and philosophy, and he was soon associated or in correspondence with Wieland, Goethe, Herder, Lessing, Hamann, Lavater, Richter, Kant, Fichte, Reinhold, and other leading thinkers. His country seat at Pempelfort, near Dusseldorf, was after Weimar and the university towns the most remarkable literary centre in Germany. On the French invasion in 1794 he took refuge in the north of Germany, and passed ten years in Wandsbeck, Hamburg, and Eutin, engaged in literary and philosophical studies, till in 1804 he was called to Munich as a member of the newly formed academy of sciences, of which he became president in 1807. He resigned in 1813, but the title and salary were continued to him till his death.
In youth Jacobi had been led to singularly intense religious and philosophical meditations. At the age of eight the idea of eternity struck him so clearly and forcibly that he fell fainting with a shriek. The thought of annihilation and the perspective of an infinite duration long weighed equally upon his mind as terrible and insupportable conceptions. The perusal of Kant's tractate on the proofs for the being of a God produced on him the most violent palpitation of the heart. He at length was able to check this susceptibility, but even in 1787 he affirmed his belief that, if he should yield to it, a few successive shocks would kill him. His first works were the philosophical romances Wolde-mar (Flensburg, 1779) and Eduard Allwill's Briefsammlung (Konigsberg, 1781), the former of which reveals his ethical system, making morality a matter of instinctive sentiment, rational intuition, or divine impulse. It was never his purpose to develop any connected system, and his philosophical writings are all brief. The first was Ueber die Lehre des Spinoza, in Briefen an Mendelssohn (Breslau, 1785), in which he assails Spinozism as a type of all formal, rationalistic, demonstration-seeking systems.
His doctrine is more fully developed in his dialogue entitled David Hume uber den Glauben, oder Idealismus und Realismus (Breslau, 1787). His relation to the Kantian critical philosophy appeared in his essay Ueber das Unternehmen des Kriticismus, die Vernunft zu Verstande zu bringen (1802). His principal works, besides those already mentioned, are Sendschreiben an Fichte (Hamburg, 1799), and Von den gottlichen Dingen und Hirer Offen-barung (Leipsic, 1811), which occasioned a controversy with Schelling. His collected works were published at Leipsic (6 vols., 1812-'24), to which his letters were added (2 vols., 1825-7). II. Johann Georg, a German poet, brother of the preceding, born in Dussel-dorf, Dec. 2, 1740, died in Freiburg, Baden, Jan. 4, 1814. After studying theology and literature at Gottingen, he was appointed in 1765 professor of philosophy and eloquence at Halle, became soon after intimately associated with Gleim, in 1769 received a canonry at Halberstadt, and devoted himself to poetry till in 1784 he became professor of belles-lettres at Freiburg. His poems are marked especially by grace and purity of diction.
His complete works were published at Zurich (7 vols., 1807-22). HI. Maximilian, a German physician, son of F. H. Jacobi, born in Dussel-dorf, April 10, 1775, died at Siegburg, near Bonn, May 18, 1858. He studied at Jena, Gottingen, Edinburgh, and Erfurt, was for a time assistant in a London hospital, and afterward director of an insane asylum at Salzburg. He early embraced the views of Pinel and Tuke on the subject of non-restraint, and sought to introduce them throughout Germany. About 1820 he was selected to take charge of the insane hospital at Siegburg. He published several essays on the treatment of the insane, and a work on "Construction and Management of Lunatic Hospitals" (1834), and was a frequent contributor to the Allgemeine Zeitschri/t fur Psychiatric. On the 50th anniversary of his doctorate (1857) a festival was held in his honor, attended by distinguished men from England and France as well as from every part of Germany. At this festival an association was organized called the Jacobi foundation, for the improvement of physicians, officers, nurses, and attendants in the care of the insane.
I. Karl Gustav Jakob, a German mathematician, born in Potsdam, Dec. 10,1804, died in Berlin, Feb. 18, 1851. In 1825, on the recommendation of Hegel, he was sent to Konigsberg as instructor in mathematics, and in 1827 was appointed professor of mathematics there. In 1842 he made a journey to England, but on his return was obliged by ill health to resign his professorship, and after visiting Italy resided in Berlin. His importance in the history of mathematics is chiefly due to his discoveries in the theory of elliptic functions, and his principal work is the Fundamenta Nova Theorio3 Functionum Ellipticarum (Konigsberg, 1829), besides which he wrote many special memoirs. Under him, Bessel, and Neumann, the university of Konigsberg enjoyed a reputation as a school of mathematics surpassed by none in Europe. II. Moritz Hermann, a German savant resident in Russia, brother of the preceding, born in Potsdam, Sept. 21, 1801, died in St. Petersburg, March 10, 1874. At the age of 28 he went to Russia to seek his fortune, and soon attracted attention by his researches in physics.
In 1830 he constructed a short electric telegraph in St. Petersburg, and in 1832 one of 18 miles between two of the imperial residences, on which he made many experiments, and the important discovery that the earth could be used to complete the electric circuit. In 1837, simultaneously with Thomas Spencer of Liverpool, he invented the process of electrotyping; and in 1840 he published Die Galvanoplastik, which gained him admittance into the imperial academy of St. Petersburg. He soon after proposed to the czar the formation of a regiment of galvanic sappers, to be trained in the management of electricity. An immense battery was constructed for him, and he received the title of colonel in the galvanic regiment. He published many memoirs on the applications of electro-magnetism in the collections of the academy of St. Petersburg.