
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 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.
Jacobi's first electromotor 
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 fullscale 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 electromotor 


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 batterypowered 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 I^{2}R', while the power dissipated in the battery is I^{2}R. 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 counteremf was unknown,
at the time. However, it was adopted as a maxim that the internal resistance
equaled the load resistance for maximum power.





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 counterinduction 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 TsarskoieSelo" (ib.); "Ueber
galvanische MessingReduction" (ib.); "Galvanische und electromagnetische
Versuche" (ib., 1845  47, 1848  50); "Vorlaufige Notiz uber galvanoplastische
Reduction mittelst einer magnetoelectrischen 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 electroaimant, entre les poles duquel un disque metallique est mis
en mouvement" ("Comptes Rendus", 1872). He also published some books in
Russian.