The blacksmith's motor.
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.
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.
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.
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 halfwrong 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. AndreMarie 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 horseshoeshaped 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 oreseparating 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.
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, resuiting in continuous rotation.
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 expectation. 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 Intelligence, 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.
RELATED ARTICLE: Which Way to Turn
While all rotating electric machines work on the same principle of relative motion between interacting magnets, there are great differences in construction and the specific mathematical models that describe the operation. Alternating current machines are generally easier to construct but are more difficult to understand. The analysis of electric machines is generally the domain of electric power engineers, but the invention and development of electric apparatus has traditionally been, and remains, largely a mechanical endeavor. The fundamental requisites for electrification are the generators and motors that allow mechanical power to be converted to electricity and back to mechanical power, via the medium of magnetism. Every rotating electric machine has a magnet associated with the rotor and another based in the outer frame or stator. In a motor, the rotor is allowed to turn in the direction of magnetic force and electric power is converted into mechanical power. In a generator, an engine or turbine drives the rotor against the direction of magnetic force, converting mechanical power to electricity.
Frank Wicks is a professor of mechanical engineering at Union College in Schenectady, N.Y.
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|Title Annotation:||electric motor inventor Thomas Davenport; includes related article on rotating electric machines|
|Comment:||The curiosity of a poor, but self-educated blacksmith named Thomas Davenport led to his inventing the first rotating electric machine, which transformed his life and would eventually transform the life of nearly everyone on Earth.|
|Date:||Jul 1, 1999|
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