| The electromagnet developed from a series of observations.
In 1820 Hans Christian Oersted (1777-1851) discovered that a current-carrying
wire set up a magnetic field. In the same year, André-Marie Ampère
(1775-1835) discovered that a helix of wire acted like a permanent magnet,
and Dominique François Jean Arago (1786-1853) found that an iron
or steel bar could be magnetized by putting it inside the helix of current-carrying
wire. Finally, William Sturgeon (1783-1850) found that leaving the iron
inside the coil greatly increased the resulting magnetic field. Sturgeon
also bent the iron core into a U-shape to bring the poles closer together,
thus concentrating the magnetic field lines.
Sturgeon insulated the iron and wound bare wire on it, but Joseph Henry (1799-1878) took the final step of insulating the wire. His largest electromagnet, built in 1832, could lift 3600 pounds One of his original electromagnets is in the Smithsonian Institution collection. The unsigned electromagnet at the right is at Washington and Jefferson College. |
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This is an electromagnet with three poles! This
one is from Queen of Philadelphia ($4.50 in the 1867 catalogue), and is
the collection of Grinnell College.
The two halves of the winding are continuous, but are
in opposite directions. Thus, the poles have the arrangement I do not know who developed this demonstration, but the earliest record of it I have seen in the 1842 edition of Daniel Davis's Manual of Magnetism.
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Here are two electromagnets of very different size.
At the left is the Great Electromagnet made by the Maynooth (Ireland) village
blacksmith in 1836 for Nicholas Callan of St. Patrick's College. It is
1.7 m in length and contains 210 pounds of iron. The coil has 490 ft of
copper wire, 1/6 in. in diameter. When equipped with a secondary winding,
this was the world's first Induction
Coil .
On the right is a mystery piece of apparatus from Vassar College with a wooden base clearly made by Ritchie of Boston. While it may be just an electromagnet, it could be the lower half of Froment's Motor. |
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This horizontal helix on a stand was probably made
by Daniel
Davis or one of his successors at some time after ca. 1850. The hollow
coil produces a magnetic field that is enhanced when an iron bar is placed
inside.
The helix is in the Greenslade Collection.
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| The electromagnet at the right is in the Garland Collection
of Classical Physics Apparatus at Vanderbilt University in Nashville, Tennessee.
It has no maker's mark, but a similar electromagnet was sold for $3.50
by Queen of Philadelphia in the 1888 catalogue.
This electromagnet follows the tradition of having the
current-carrying coils painted dark green; permanent magnets were invariably
painted red.
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The 1851 catalogue of Daniel Davis, Jr. of Boston shows
an electromagnet very much like this one in the apparatus collection of
the University of Vermont, but without the wooden base. Davis apparatus usually
has the coils painted green and the soft-iron core painted red, as in this
case. The Davis electromagnet was priced at $0.75 to $1.00.
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| The electromagnet at the right was made by John Millington
when he was the Professor of Chemistry, Natural Philosophy and Engineering
at the College of William and Mary in Williamsburg, Virginia. On the bottom
is written his name, the date 1837 and the word "Philadelphia". The last
two pieces of data are confusing, as Millington worked as an apparatus manufacturer
in Philadelphia from 1832 to 1835.
The design is similar to that used by Joseph Henry in 1829 in which insulated wire was wound around the U-shaped armature; in William Sturgeon's 1825 design bare copper wire was wound around an insulated armature. Following Henry's design, the keeper is pivoted to allow a weight to be hung on one side, thus allowing the lifting power of the electromagnet to be studied as a function of the current passing through the wire. The apparatus is in the collection of the University Museum of the University of Mississippi, where Millington taught from 1848 to 1853. |
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This is a small picture for a large electromagnet. The magnet is part of a system of demonstrations at the department of physics at the University of texas in Austin. It is unmarked, but I think that it is probably German from the early part of the 20th century. The magnet moves, with some difficulty, on a solid four-wheel wagon, and the poles are about four feet off the ground. The system can be configured as a motor, can be used to demonstrate the paramagnetism of liquid oxygen, etc. |
| The electromagnet at the right is at the "Large Electromagnet for diamagnetic and paramagnetic experiments" listed at 550 marks (about $130) in the 1900 Max Kohl catalogue. Originally it was equipped with heavy-duty casters to enable it to be moved around, but at some point the demonstration room personnel at Cornell University put it on a sturdy cart so that it could be seen in lecture demonstrations. The coils should be painted red, and the base, gloss black. |
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The electromagnet at the left is unmarked, but I suspect that it was part of a large set of apparatus bought in the late 1920s from Max Kohl of Chemnitz, Germany by Hobart and William Smith Colleges in Geneva, New York. The soft-iron keeper, with a ring for suspending masses, is missing. It is 55 cm high. |