ARTICLE
BY DR. FRANK WICKS:
As
published in Mechanical
Engineering magazine in July 1999.
© 2010 ASME. Used with permission.
The Blacksmith's Motor
Electricity, magnetism, and motion:
A self-taught Vermonter pointed the direction for lighting the
world.
By Frank Wicks
In the spring
of 1833, a self-educated but impoverished blacksmith in Forestdale,
Vt., by the name of Thomas Davenport heard some curious news.
This news, as it turned out, would not only change his life but
would eventually change the life of almost everyone on earth.
Davenport's curiosity led to his invention of the first rotating
electric machine. Today, we would describe it as a shunt-wound
brush and commutator dc motor.
Thomas Davenport,
inventor of the electric motor, was a self-educated blacksmith
with a passion for reading.
The momentous news that roused the blacksmith's
curiosity was that the Penfield and Hammond Iron Works, on the
other side of Lake Champlain in the Crown Point hamlet of Ironville
in New York state, was using a new method for separating crushed
ore. The process used magnetized spikes mounted on a rotating
wooden drum that attracted the millings with the highest iron
content. Higher-purity feedstock could be fed to the furnaces,
improving their productivity and the quality of the iron they
produced. This was important, since the recent introduction and
expected rapid expansion of railroads were dramatically increasing
the demand for quality iron.
This process had been developed by Joseph
Henry of Albany, N.Y. It used an electromagnet that he had designed
to magnetize the spikes; in fact, Henry's electromagnet was said
to be powerful enough to lift a blacksmith's anvil. Its use in
the iron ore separation process was the first time that electricity
had been used for commercial purposes, thus beginning the electric
industry.
Thomas Davenport had no prior knowledge
of discoveries in magnetism and electricity when this new process
stimulated his interest. He had been born in 1802 on a farm outside
Williamstown, Vt., the eighth of 12 children. His father died
when Thomas was 10. Schooling opportunities were minimal, and
at the age of 14 Thomas was indentured for seven years to a blacksmith.
His room and board and six weeks per year of rural schooling were
provided in return for service in his master's shop. The work
was hard, but the boy was later remembered for his curiosity,
his interest in musical instruments, and his passion for books.
Once he was liberated in 1823, Davenport
traveled over the Green Mountains to Forestdale, a hamlet in the
town of Brandon, Vt., where there was an iron industry. He set
up his own marginally successful shop, married the daughter of
a local merchant, and started a family.
His only means of learning was self-education.
When the news from the ironworks piqued his curiosity, he acquired
books and journals, and started reading about the experiments
and discoveries that were beginning to unlock some of the mysteries
of electricity and magnetism.
Electric
Currents
It was more than 80 years since Benjamin
Franklin, in 1752, had experimented with static electricity from
Leyden jars and with electricity from the sky, by flying a kite
over Philadelphia during a storm.
Davenport's model of an electric "train."
The circular track is 4 feet in diameter. Power was supplied from
a stationary battery to the moving electric locomotive, using
the rails as conductors for the electricity.
A new era had started in 1800, when Alessandro
Volta demonstrated an electric pile, which was a battery that
produced electricity directly from a chemical reaction between
two different metals. Static electricity batteries such as the
Leyden jar had provided only sudden electric pulses during discharge.
For the first time, investigators could draw a continuous electric
current for hours, instead of relying on an erratic spark in a
Leyden jar.
In 1820, the Danish experimenter Hans Oersted
showed that Franklin had been half-wrong in his conclusion that
electricity and magnetism were unrelated. Oersted observed that
the needle of a nearby compass moved when he closed the circuit
through a wire and battery. This demonstrated that electricity
was causing magnetism. Andre-Marie Ampere in France soon showed
that the magnetic effect could be multiplied by coiling the wire.
William Sturgeon went the next step in 1825 by wrapping an uninsulated
coil of wire around an insulated horseshoe-shaped iron core, thus
making the first electromagnet, which lifted about 5 lbs.
Now that it was shown that electricity
could produce magnetism, the reverse question arose: whether magnetism
could produce electricity. The first attempts consisted of holding
a magnet near a wire. No electricity was observed. Then, in 1831,
Michael Faraday succeeded in producing electricity by means of
magnetism when he moved a disc perpendicular to a magnetic field.
Almost simultaneously, Joseph Henry, inventor of the ore-separation
process that so excited Davenport, used a more powerful lifting
magnet of his own design to show that electricity could be produced
from magnetism by changing the strength of the magnet.
The discovery that magnetism could cause
electricity was a vital step toward the modern electric world.
The only previously demonstrated techniques for producing electricity
had been the limited-potential static electric generator of von
Guericke and the chemical reaction battery of Volta.
Joseph Henry was to become the only American
to have his name applied to a unit of electricity: A henry is
a measure of electric inductance. Henry had started his pioneering
work in electricity and magnetism as a professor at Albany Academy
in 1826. In 1833, he moved on to Princeton. He ended up as the
founding secretary of the Smithsonian Institution, where he served
from 1846 until 1878.
While at Albany, Henry developed an electromagnet
that could lift a phenomenal 2,000 lbs. He did this by wrapping
a mile of insulated wire in several parallel circuits around a
soft iron core that he procured from the Crown Point Iron Works,
the company for which he eventually designed the machine that
used his ore-separating electromagnet.
The iron separation technique developed
by Henry was, in a sense, the magnetic equivalent of the cotton
gin. That device, invented in 1794 by Eli Whitney, used spikes
on a rotating drum to comb the seed from the fiber. For the first
time growing cotton was profitable, because a single worker could
produce 50 lbs. of pure cotton per day. Threshing machines were
being built on a similar principle. The ancient process of beating
the wheat with a wooden flail to separate the grain from the chaff
was to be replaced by spikes on a rotating drum.
Davenport
Invents the Motor
Soon after he learned of the Henry magnet,
Davenport traveled the 25 miles to Crown Point on a horse to witness
the wonders of magnetic lifting power. The amazing sight further
inflamed his interest. He decided to travel another 80 miles south,
to Albany, to meet Henry, only to find out that he had moved down
to Princeton.
Returning home out of money, Davenport
called upon his brother, a peddler, to join him with his cart
for another trip to Crown Point. Once there, they auctioned the
brother's products and traded a good horse for an inferior one
to obtain money to buy the magnet. When they got home, the brother
suggested trying to recover the cost by exhibiting the magnet
for a fee.
Davenport traveled 25 miles to Crown Point
on a horse to witness the wonders of magnetic lifting power.
Thomas Davenport had other plans. He unwound
and dismantled the magnet as his wife, Emily, took notes on its
method of construction. He then started his own experiments and
built two more magnets of his own design. Insulated wire was required,
but only bare wire was available. Emily Davenport cut up her wedding
dress into strips of silk to provide the necessary insulation
that allowed for the maximum number of windings.
The electricity source for the magnets
was a galvanic battery of the type developed by Volta. It used
a bucket of a weak acid for an electrolyte. The bucket contained
concentric cylinders of different metals for electrodes; these
were wired to provide external electric current to the magnet.
Davenport mounted one magnet on a wheel;
the other magnet was fixed to a stationary frame. The interaction
between the two magnets caused the rotor to turn half a revolution.
He learned that by reversing the wires to one of the magnets he
could get the rotor to complete another half-turn. Davenport then
devised what we now call a brush and commutator. Fixed wires from
the frame supplied current to a segmented conductor that supplied
current to the rotor-mounted electromagnet. This provided an automatic
reversal of the polarity of the rotor-mounted magnet twice per
rotation, resulting in continuous rotation.
This Patent Office model of Davenport's
motor now sits in The Smithsonian Institution in Washington. Reading
about experiments and discoveries sparked DavenportÕs interest,
and led to his invention of the electric motor.
The motor had the potential to drive some
of the equipment in Davenport's shop, but he had even bigger ideas.
The era of the steam locomotive and railroads was just beginning,
but already boiler failures and explosions were becoming frequent,
tragic occurrences. Davenport's solution was the electric locomotive.
He built a model electric train that operated on a circular track;
power was supplied from a stationary battery to the moving electric
locomotive using the rails as conductors to transmit the electricity.
When Davenport traveled to Washington to
obtain a patent, however, his application was rejected: There
were no prior patents on electric equipment.
He started a tour of colleges to meet professors
of natural philosophy who might examine his invention and provide
letters of support to the patent office. His travels took him
to the new Rensselaer Institute in Troy, N.Y., recently founded
(in 1824) as the nation's first engineering school by Stephen
Van Rensselaer.
The last of eight generations of land-owning
patroons, Van Rensselaer had been a commissioner overseeing the
construction of the Erie and Champlain canals, opened in 1825.
The school had been charged with a mission to qualify teachers
for instructing the sons and daughters of farmers and mechanics
in developing methods of applying science to the common purposes
of life.
Davenport met Rensselaer's founding president,
Amos Eaton, a distinguished lawyer, botanist, geologist, chemist,
educator, and innovator, who was amazed by the motor and by the
self-educated blacksmith who had built it. Eaton arranged an additional
exhibit for the citizens of Troy, and Stephen Van Rensselaer himself
bought Davenport's motor for the school. The nation's first engineering
school now possessed the world's first electric motor.
With the sale of his motor, Davenport was
able to buy a quantity of already insulated wire, and he returned
home to build another motor. He traveled to Princeton to meet
Joseph Henry and then to the University of Pennsylvania to meet
Professor Benjamin Franklin Bache, Benjamin Franklin's grandson
and an outstanding scientist.
The self-educated blacksmith, having now
impressed the most prominent men of learning in the country, returned
to the patent office with letters and a working model. His troubles
were not yet over, however. The model was destroyed by fire before
it was examined. He built another and tried again. At last, the
first patent on any electric machine was issued to Thomas Davenport
for his electric motor on Feb. 25, 1837.
The scientific community and the media
responded with great excitement and high expectations. Benjamin
Silliman, the founder of Silliman's Journal of Science, wrote
an extended article and concluded that a power of great but unknown
energy had unexpectedly been placed in mankind's hands. The New
York Herald proclaimed a revolution of philosophy, science, art,
and civilization: "The occult and mysterious principle of
magnetism is being displayed in all of its magnificence and energy
as Mr. Davenport runs his wheel."
Davenport set up a laboratory and workshop
near Wall Street in hopes of attracting investors. Samuel Morse,
who in 1844 would commercialize the telegraph, came to observe.
To further advertise his motor, Davenport established his own
newspaper, The Electro-Magnet and Mechanics Intelligencer, and
used his electric motor to drive his rotary printing press.
The motor was a spectacular technological
success, but it was becoming a commercial failure. No one knew
how to predict the amount of energy in chemical batteries, and
a battery-powered motor could not compete with a steam engine.
Funds were promised but not delivered. Bankrupt and distressed,
Davenport returned to Vermont and started writing a book describing
his work and his vision for his electric motor. He died in 1851
at the age of 49, leaving only a prospectus.
The
Motor Keeps Running
What Davenport could not anticipate, and
what no one else would describe for another 20 years, was that
his motor would be turned by water or steam power and would operate
in reverse, as an electric generator. Within 40 years of his death,
electric-powered trains and trolleys had become common, with Davenport's
machine creating electricity at the power station and his motor
then converting this electricity back to mechanical power to move
the cars.
Thomas Edison invented the electric lightbulb
in 1879, using a chemical battery to power his experiments, but
he recognized the need for central generating plants and distribution
systems to provide electricity to customers. In 1882, his Pearl
Street station in lower Manhattan used steam engines to drive
shunt-wound brush and commutator dc generators of the type that
Thomas Davenport had invented 45 years earlier. Recognizing that
expanding demand would require a massive new manufacturing and
service industry, Edison started a manufacturing facility in Schenectady
that would become the General Electric Co. The company's first
products were motors and generators that copied the design and
principles of Thomas Davenport's motor.
When Edison died in 1931, it was suggested
that all the electricity should be turned off for five minutes
in recognition of the great inventor, but such an action was judged
to be practically impossible. The ultimate tribute to Edison was
that within his lifetime the benefits of his inventions had become
such a vital part of daily life.
Davenport died 30 years before the world
was ready for his invention. Today, the electrification of the
world and electricity's myriad of now-vital uses can be seen as
the greatest technological marvel in human history. Electric light
has extended full human activity to 24 hours per day. Electric-powered
refrigeration is now taken for granted. Air conditioning has made
the most inhospitable regions comfortable for year-round living
and spawned new major cities. Our communications, computing, and
information systems could not exist without electricity. Thomas
Davenport, though little remembered today, played a vital part
in making all of this possible.
As
published in Mechanical
Engineering magazine. © 2010 ASME. Used with permission.
See more articles about engineering written by members of the
Edison Tech Center at the Engineering
Forum
