Jacobi

Moritz Hermann Jacobi was a German physicist and engineer, but he worked mainly in Russia. His works on galvanoplastics, electric motors, and wire telegraphy were of great applied significance.

Moritz Hermann Jacobi, 1836

Moritz Hermann Jacobi was a German physicist and engineer. He was born om September 21, 1801, in Potsdam, Germany. Jacobi graduated from the Getingen University and in 1834 he moved to Kenigsberg where he worked as an architect. In 1835 Jacobi received professorship at the Derpt University, but two years later, in 1937, he decided to move to St. Petersburg. Jacobi worked as a leading researcher at the Academy of Sciences in St. Petersburg alongside others such as the chemist Mendeliev. Jacobi was one of a rising number of physicists working on the practical applications of electricity, and engaged in a number of studies of great interest in the fast developing subject.

Moritz Hermann Jacobi, 1837

Jacobi's first electro-motor

In his first work, reported to the St Petersburg Academy, he described his investigation of the power of an electromagnet in relation to the design of motors and generators, and discussed his efforts to construct the first full-scale practical motor in May 1834. He carried out a number of tests on the motor for instance measuring its output by determining the amount of zinc consumed by the battery.

One more modification
of Jacobi's electro-motor

In 1838 Jacobi discovered galvanoplastics (also called electrotyping) and through his success and the presentations he gave, he promoted this specialist field and the application of galvanoplastics and electroplating in Europe. This medal is memorizing Jacobi's contribution to the development of galvanoplastics.

Electrotyping is electroforming process for making duplicate plates for relief, or letterpress, printing. The process was first announced in 1838 by M.H. von Jacobi, a German working in St. Petersburg, Russia. Thomas Spencer and C.J. Jordan of England and Joseph A. Adams of the United States produced similar results the following year. An electrotype, or electro, is made by electroplating a thin shell of copper or other metal onto a mold, usually wax, of the original cut or type form and then removing the mold and backing the shell with metal. More durable than type and cuts, electros are used instead of the original for long press runs, to avoid wear and damage to expensive type and halftones or linecuts. Electrotypes also can duplicate and replace linoleum cuts, woodcuts, and wood engravings.

In 1839 Jacobi, with the financial assistance of Czar Nicholas, constructed a 28–ft boat propelled by an electric motor with a large number of battery cells. It carried 14 passengers on the Neva River at a speed of three miles per hour. His hopes of covering the Neva with a fleet of magnetic boats were doomed from the beginning, however, by the cost of battery-powered operation and by the fumes that such batteries emitted.

In the course of these experiments, he considered how much power he could get out of a battery. A battery can be represented as an electromotive force E in series with an internal resistance R which are about constant and do not depend much on the current that is drawn. If the external load is a resistance R', then the current is I = E / (R + R'). The power dissipated in the load is I²R', while the power dissipated in the battery is I²R. If R' = 0, there is no external power. If R' is infinitely large there is also no power, since I = 0. Therefore, for some intermediate value of R' there must be a maximum power. Calculus gives the result easily, but a little reasoning also shows that maximum power is attained when R' = R (imagine interchanging R and R'). Hence the theorem: Maximum power is transferred when the internal resistance of the source equals the resistance of the load. We should carefully note the condition that is seldom added: When the external resistance can be varied, and the internal resistance is constant.

Jacobi quite correctly concluded that electric motors were uneconomic, considering the high price of zinc and the 50% loss of energy. The concept of energy was as yet somewhat hazy, and the fact that mechanical work out was equal to the electrical work done against a counter-emf was unknown, at the time. However, it was adopted as a maxim that the internal resistance equaled the load resistance for maximum power.

**Jacobi also contributed to the development of telegraph. Some examples of his telegraph devices are show here:**

Jacobi was influenced by the earlier theoretical discoveries of Georg Ohm, and the work of his contemporaries Michael Faraday and Emil Lenz, and in turn his work influence James Joule. Jacobi's discovery of the counter-induction effect which set a limit to the efficiency of electromagnetic engines led Joule to calculate to his dismay that the efficiency of the electromagnetic engines that he could build would be much lower that of the existing steam engine.

Jacobi's publications include: "Benutzung der Naturkrafte zu menschichen Arbeiten" (1834); "Ueber die Construction schief liegender Raderwerke" ("Crelle's Journal der Math.", 1827); "Ueber den Einfluss der Chausseen, Eisenbahnen und Wasserverbindungen auf den Nationalreichtum" (ib.); "Memoire sur une machine magnetiqne". "Comptes Rendus", 1874); "Memoire sur l'application de l'Electromagnetisme au Mouvement des machines" (1835); "Eine Methode die Constanten der Voltschen Ketten zu bestimmen" ("Bull. de l'Acad.", 1842); "Beschreibung eines verbesserten Voltagometers" (ib.); "Ueber die Entwickelung der Galvanoplastik" (ib., 1843); "Ueber die galvanische Vergoldung" (ib.); "Einige Notizen uber galvanische Leitungen" (ib.); "Ueber die Gesetze der Electromagnete" (mit Lenz), (ib., 1844); "Notice preliminaire sur telegraph electromagnetique entre St.-Petersburg und Tsarskoie-Selo" (ib.); "Ueber galvanische Messing-Reduction" (ib.); "Galvanische und electromagnetische Versuche" (ib., 1845 - 47, 1848 - 50); "Vorlaufige Notiz uber galvanoplastische Reduction mittelst einer magneto-electrischen Maschine" (ib., 1847); "Ueber eine Vereinfachung der Uhrwerke, welche zur Hervorbrin gung einer gleichformigen Bewegung bestimmt ist" (ib., 1848); "Sur les telegraches electriques" (ib., 1849); "Sur la theorie des machines electromagnetiques" (ib., 1851); "Die galvanische Pendeluhr" (ib.); "Sur la necessite d'exprimer la force des courants electriques et la resistance des circoits en unites unanimement et generalement adoptees" (ib., 1858); "Sur quelques experiences concernant la mesure des resistances" (ib., 1859); "Note sur la production de depots de fer galvanique" (ib., 1869); "Confection d'etalons prototypes, destines a generaliser le systeme metriques" ("Comptes Rendus", 1869); "Notice sur l'absortion de l'hydrogene par le fer galvanique" ("Bul. de l'Acad.", 1870); "Application des batteries secundaires ou de polarisation aux moteurs electromagnetiques" (ib., 1871); "Sur la fabrication des etalons de longeur la galvanoplastie" (ib., 1872); "Une reduction du fer par l'action d'un puissant solenoide electromagnetique" (ib., 1873); "Courants d'induction dans les bobines d'un electro-aimant, entre les poles duquel un disque metallique est mis en mouvement" ("Comptes Rendus", 1872). He also published some books in Russian.


	*Jacobi's electro-motor, 1834, Deutsches Museum*