# Moritz von Jacobi

(Redirected from Boris Jacobi)
Moritz Hermann von Jacobi
Moritz Hermann von Jacobi
Born 21 September 1801
Died 10 March 1874 (aged 72)
Residence Prussia, Russian Empire
Nationality German
Known for Maximum power theorem
Scientific career
Fields Physics, Engineering

Moritz Hermann (Boris Semyonovich) von Jacobi (Russian: Борис Семёнович (Морис-Герман) Якоби) (21 September 1801 – 10 March 1874) was a German and Russian engineer and physicist born in Potsdam. Jacobi worked mainly in Russia. He furthered progress in galvanoplastics, electric motors, and wire telegraphy. His family was Jewish.[1]

## Motors

In 1834 he began to study magnetic motors. In 1835 moved to Dorpat (now Tartu, Estonia) to lecture at Dorpat University. He moved to Saint Petersburg in 1837 to research usage of electromagnetic forces for moving machines for Russian Academy of Sciences. He investigated the power of an electromagnet in motors and generators. While studying the transfer of power from a battery to an electric motor, he deduced the maximum power theorem. Jacobi tested motors output by determining the amount of zinc consumed by the battery. With financial assistance of Czar Nicholas, Jacobi constructed in 1839 a 28-foot electric motor boat powered by battery cells. The boat carried 14 passengers on Neva river against the current. The boat fared at the speed of three miles for hour.

## Jacobi's Law

Circuit Diagram

Power is being transferred from the source,
with voltage V and resistance RS,
to a load with resistance RL,
resulting in a current I. I is simply
the source voltage divided by the total

circuit resistance

The law known as the maximum power theorem states:

"Maximum power is transferred when the internal resistance of the source equals the resistance of the load, when the external resistance can be varied, and the internal resistance is constant."

The transfer of maximum power from a source with a fixed internal resistance to a load, the resistance of the load must be the same as that of the source. This law is of use when driving a load such as an electric motor from a battery. Jacobi obtained his theorem by applying common sense[citation needed].

## Electrotyping and telegraphy

In 1838, he discovered galvanoplastics, or electrotyping, a method of making printing plates by electroplating. The way in which this works is analogous to a battery acting in reverse. The stereotype was an impression taken from a form of movable lead type and used for printing instead of the original type. This technique is used in relief printing.

He also worked on the development of the electric telegraph. In 1842-1845 he built a telegraph line between Saint Petersburg and Tsarskoe Selo using an underground cable. In 1867 he was a Russian delegate to the Commission on measurement units at the Paris World's Fair. He was a strong proponent of the metric system.

## Naval mine

In 1853, Jacobi developed the Jacobi naval mine. The mine was tied to the sea bottom by an anchor, a cable connected it to a galvanic cell which powered it from the shore, the power of its explosive charge was equal to 14 kilograms (31 lb) of black powder. Its production was approved by the Committee for Mines of the Ministry of War of the Russian Empire and in 1854 60 Jacobi mines were laid in the vicinity of the Forts Pavel and Alexander (Kronstadt).[2]

## Family

He was a brother of the mathematician Carl Gustav Jacob Jacobi.[3]

Von Jacobi's tomb, from wife and children

## Notes

1. ^ Pieper, H. (2005). Der Euler des 19. Jahrhunderts: CG Jacob Jacobi. Elemente der Mathematik, 60(3), 89-107.
2. ^ Tarle, Yevgeny (1944). Крымская война [Crimean War] (in Russian). II. Moscow: Soviet Academy of Sciences. pp. 44–45.
3. ^  Gilman, D. C.; Peck, H. T.; Colby, F. M., eds. (1905). "Jacobi, Moritz Hermann". New International Encyclopedia (1st ed.). New York: Dodd, Mead.