| Paul-Gustav Froment (1815-1865) was a French engineer
who devised a number of scientific instruments. He worked with Foucault
on his pendulum that demonstrated the rotation of the earth, and worked
with Hughes on his
telegraph system. In 1844 he devised an electric motor that was one of
the first used for industrial purposes. In his design, electromagnets are
energized to pull in iron bars mounted on a revolving cage. Once the iron
bar is level with the electromagnet, the current is cut off until the next
iron bar is in range. A commutator is used to complete and then break the
current to the electromagnet.
The Froment motor on the right was sold by James W. Queen and Company of Philadelphia. In 1881, Queen listed the apparatus for $10.00.
| Apart from the shape of the three iron bars, the Froment
motor on the left, at Oberlin College, and the one on the right, at Transylvania
University, are identical with the instrument above from Grinnell College.
Until the early eighteen fifties, the apparatus was made by Daniel Davis of Boston under the name of the Revolving Armature Engine. In the 1851 edition of Davis's Manual of Magnetism the apparatus is listed at $6.00.
Other makers, for example, Wightman of Boston, also sold this apparatus. After Davis went out of business in the early 1850s, the apparatus was made by the successor companies, Thomas Hall and Palmer and Hall of Boston.
| The eight-pole Froment motor at the left in in the collection
of historical apparatus at St. Patrick's College in Maynooth, County Kildare,
Ireland. It is unmarked, and probably dates from the latter part of the
The iron strips are evenly spaced on the periphery of the wheel, which is 10 cm in diameter. On the near edge of the axle can be seen the eight-pointed cam that is used to make and break contact with a metal spring to energize the two-coil electromagnet.
The Froment motor at the right is also at St. Patrick's College in Maynooth, Ireland. It was made in the second half of the 19th century by the well-known firm of Yeates & Son of Dublin, which both made and imported scientific apparatus.
This is a big, heavy machine, with an overall height of 60 cm. There are four equally spaced electromagnets: the two visible at the sides and two others at the top and the bottom. Seven iron rectangles are held at the ends of struts projecting from the axle, and a four-pole ebonite commutator is used to energize the magnets as one of the pieces of iron approaches the appropriate electromagnet.
| The small Froment-type motor at the left is in the Harvard
University collection of historical instruments. It is unmarked.
Here there are six iron blocks, and the driving electromagnets are offset so that they may be energized alternately to provide twelve power pulses per revolution.
|This small water pump driven by a Froment-type motor is in the collection of Harvard University. The two sets of six iron vanes are attracted to the ends of the electromagnet through a non-visible make- and-break mechanism.|
| During the period from about 1890 to 1910, students in
the second-year physics course at Denison University in Granville, Ohio
built apparatus as part of their course.
This unmarked Froment motor probably dates from that era. However, the design is inverted, with the five sets of iron attractors being at rest, while the four pairs of electromagnets revolved inside. The commutator can be clearly seen on the right-hand side of the coil assembly.
| The unmarked philosophical toy at the right-hand side
is in the collection of the National Museum of American History of the
Smithsonian Institution in Washington, D.C.
This has some of the marks of the Froment motor, including
the electromagnet and the iron bar on which the figure stands. The repetitive
motion is supplied by oscillation instead of rotation. However, I cannot
remember where the make and break connections to energize the electromagnet