The Electromagnetic Engine

Updated: 18 Mar 2010

dal Negro bio added

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In the very earliest days of electric motors, it was far from clear that a rotary format was the best solution, and many scientists and inventors took their inspiration from horizontal steam engines. It is clear now that they were on the wrong track, as it is equally clear that for steam engines, a rotary system was not the way to go. See Rotary Steam Engines.

This page is dedicated solely to electric engines that convert reciprocating to rotary motion by a crank or equivalent. There were many, although the reciprocating electric engine proved to be the deadest of technological dead ends. Only a small sample are shown here.

Most electric engines were essentially solenoids that pulled a piece of iron into their centre when energised. This was coupled by a connecting rod to a crank and flywheel, just as in a steam engine. A set of contacts switched the solenoid current on and off at the appropriate times so the iron could be drawn out again by the flywheel and continous motion obtained.


The American scientist Joseph Henry (1797-1878) constructed a small electromagnetic engine, with a reciprocating beam. He called it as a "philosophical toy", and there was certainly no intention of getting useful work out of it. It was first described in American Journal of Science, 1831, Vol 20 p342. In a British journal Philosophical Magazine in 1838, F Watkins examined Henry's invention in detail and described it as the first cyclic electric motor, ie one that continued working without manual switching or resetting.

Left: The Henry magnetic rocker: 1831

I have yet to find a detailed description of the machine, but I believe its operation was thus: On either side is a primary battery, with a small cup of mercury mounted on each terminal. When the two wires o,p make contact with these a winding on rocker AB is energised and AB is repelled by the bar magnet C. This breaks the connection, but the inertia of AB swings it over so that the other pair of wires q,r now make contact with the other battery and now AB is repelled by bar magnet D, and the cycle continues.

Left: The Henry magnetic rocker: 1831

This appears to be a modern reconstruction.

Joseph Henry did much work on electromagnetism and in 1893, his name was given to the standard electrical unit of inductance, the Henry.


Salvatore dal Negro, an Italian, built in 1832 the first electric engine with a quantifiable power outout. Rotary motion was obtained from a pendulum with a rachet device, and it could lift 60 grams by 5 centimeters in one second and so hence developed nearly 30 mW of mechanical power.

Dal Negro described his experiments in a letter in April 1832 and later in a scientific paper: "Nuova Macchina élettro-magnetica" in March 1834. His machines are stored at the Museum of the History of Physics at the University of Padua. Unfortunately, they are not displayed.

Left: dal Negro's magnetic pendulum: 1832

The exact method of operation is not very clear from this drawing. There seems to be an upper U-shaped electromagnet, that interacts with two U-shaped permanent magnets mounted at the top of the pendulum; it is not clear if these slide or swing sideways. The pendulum is pivoted at C. The switching arrangement are not visible, unless the thing marked Q below the pendulum bob is some sort of contact.

Salvatore Dal Negro (Born 1768 in Venice; died 31 January 1839 in Padua) was an Italian priest and physicist. He came from a humble background and studied theology in Murano . In 1791 he was ordained a priest and went to Padua, becoming first an assistant, and then a lecturer in experimental physics at the University of Padua. In 1806 the Napoleonic government appointed him government professor of mechanics and experimental physics. From 1831 he experimented with electromagnets and in 1832 demostrated his electric motor.

In 1809 Dal Negro invented the Oligochronometer, an instrument for measuring very short periods of time accurately. In 1838 he was awarded the Order of the Iron Crown by the unfortunate Emperor Ferdinand I of Austria.


In 1838 or 39, the Prussian physicist Moritz Jacobi constructed the world's first electrically propelled boat, using a a reciprocating solenoidal electromagnetic engine of about 1 HP to drive two paddlewheels. It was publicly demonstrated it on the river Neva in Russia. Electric power came from a bank of chemical batteries, the fumes from which (probably nitrogen dioxide, but this detail is so far unclear) were so copious that the experiment had to be prematurely terminated.

However, Jacobi was back the next year with the same boat, but a better battery bank, a fifth the size of the previous one, and presumably less likely to poison its owner. It appears that the reciprocating engine had been replaced by a much more effective rotary motor. The 28-foot boat managed an average speed of 3 mph while carrying 12 or 13 passengers.


Luigi Magrini (1802-1868) was born in Udine, and obtained a degree in mathematics from the University of Padua in 1825. He held the chair of Physics at Florence, Italy, and worked with Leopoldo Nobili, the thermopile experimenter. See here for more on thermopiles

His reciprocating electric engine is in the Museum of The History of Science at Florence. Unfortunately photography is not permitted in the museum, so I am unable to show you the picture below.

Left: The Magrini reciprocating electric engine: circa 1840

Note that the two cranks are set at 90 degrees to avoid dead-centre problems- the engine was clearly designed to be self-starting. The switching system was a commutator on the crankshaft, not visible here.

Guiseppe Domenico Botto (1791-1865) was Professor of the University of Turin. His electric engine used swinging coils mounted on a sort of pendulum.

Left: The Botto electric engine: 1834

The upper arm of the pendulum drove a very light wheel through a crank. Switching of the current to the coils was done with mercury contact cups. Power came from 14 glass compartments in the wooden base that held chemical primary cells. (Actually, I can only count 13 in the photograph)

The Botto engine example in the Museum of The History of Science at Florence is labelled as "circa 1840" and "after Botto" which presumably means it was built by somebody else.


Charles Grafton Page of the USA was an early electrical pioneer, and also a physician, patent examiner, patent advocate, and a professor of chemistry.

Above: The Page reciprocating electric engine: 1844. Not a very expert drawing, unfortunately.

Here page very clearly took his inspiration from horizontal steam engines.

The Naming Of Parts:

Electrical input terminals
Yokes joining armatures to guide rods

This is a later design, which Page called his 'axial engine'. Two solenoids are placed in tandem to drive the flywheel through a conventional crank, alternately pulling in two cylindrical armatures, and working on both directions of movement in the same fashion as a double-acting steam engine.
The current through the solenoids was apparently switched by a commutator on the crankshaft, though this detail is not very clear in the drawing.

Page later, in 1851, built an electromagnetic engine that developed 16 horsepower; this reached 19 mph when used in a battery-powered electric locomotive on the Baltimore and Ohio railroad. it is not confirmed that this was of the reciprocating type.


Left: The patent drawing of the Depoele engine.

This patent is dated 1891, by which time it was very clear that electric motors should be rotary. Nonetheless, Charles J Van Depoele of Massachusetts thought it was worth taking out this patent.

He was almost certainly wrong.

Solenoid reciprocating engines are example of variable-reluctance electric motors. Reluctance is a measure of how hard it is for a given electromagnetic induction to set up a circuit of magnetic flux- a kind of Ohm's Law of magnetism. If a magnetic system has moving parts these naturally take up a position that results in the greatest magnetic flux, ie a position of minimum reluctance.

The familiar rotary electric motor is usually a constant-reluctance design.

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