The BLACKSMITH'S motor Electricity, magnetism, and motion: A self-taught Vermonter pointed the direction for lighting Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/121/07/66/6382341/me-1999-jul8.pdf by guest on 25 September 2021 the world. By Frank Wicks N T HE SPRING OF 1833, a self-edu­ This process had been developed cated but impoverished black­ by Joseph Henry of Albany, N.Y It I smith in Forestdale, Vt., by the used an electromagnet that he had name of Thomas Davenport heard designed to magnetize the spikes; some curious news. This news, as it in fact, Henry's electromagnet was turned out, would not only change said to be powerful enough to lift a his life but would eventually change blacksmith's anvil. Its use in the the life of almost everyone on earth. iron ore separation process was the Davenport's curiosity led to his in­ first time that electricity had been vention of the first rotating electric used for commercial purposes, thus machine. Today, we would describe beginning the electric industry. it as a shunt-wound brush and com­ Thomas Davenport had no prior mutator dc motor. knowledge of discoveries in mag­ The momentous news that roused netism and electricity when this the blacksmith's curiosity was that new process stimulated his interest. the Penfield and H ammond Iron He had been born in 1802 on a Works, on the other side of Lake farm outside Williamstown, Vt., Champlain in the Crown Point the eighth of 12 children. His fa­ hamlet of Ironville in New York ther died when Thomas was 10. state, was using a new method for Schooling opportunities were min­ separating crushed ore. The process lllt.I\I \1> Il ~ \TW(l/l'l'. imal, and at the age of 14 Thomas used magnetized spikes mounted was indentured for seven years to a on a rotating wooden drum that at­ Thomas Davenport, inventor of the electric motor, was blacksmith. His room and board a self-educated blacksmith with a passion for reading. tracted the millings with the highest and six weeks per year of rural iron content. Higher-purity feedstock could be fed to schooling were provided in return for service in his mas­ the furnaces, improving their productivity and the quali­ ter's shop. The work was hard, but the boy was later re­ ty of the iron they produced. This was important, since membered for his curiosity, his interest in musical instru­ the recent introduction and expected rapid expansion of ments, and his passion for books. rail roads were dramatically increasing the demand for Once he was liberated in 1823, Davenport traveled quality iron. over the Green Mountains to Forestdale, a hamlet in the town of Brand on, Vt., where there was an iron industry. Frank Wicks is a professor of mechanical engineering at He set up his own marginally successful shop, married Union College in Schenectady, N. Y. the daughter of a local merchant, and started a family. 66 J ULY 1999 M EC H AN ICA L ENG I NEE RI NG H is only means of learning was self-educa tion. W hen generator of von Guericke· an d the chemical reaction the news fro m the ironworks piqued his curiosity, he ac­ battery ofVolta. quired books and journals, and started reading about the ] oseph H enry was to become the only American to experiments and discoveries that were beginning to un­ have his name applied to a unit of electricity: A henry is lock so me of the mysteries of electricity and magnetism. a measure of electric inductance. H enry had started his pioneering work in electricity and magnetism as a pro­ ELECTRIC CURRENTS fessor at Albany Academy in 1826. In 1833, he m oved It was more than 80 years since Benjamin Franklin, in on to Princeton. H e ended up as the fo unding secretary 1752, had experimented with static electricity from Ley­ of the Smithsonian Institution, w here he se rve d from den jars and with electricity fro m the sky, by flying a kite 1846 until 1878. over Philadelphia during a storm. While at Albany, H enry developed an electromagnet A new era had started in 1800, when Alessandro Volta that could lift a phenomenal 2,000 Ibs. H e did this by demonstrated an electric pile, which was a battery that wrapping a mile of insulated w ire in several parallel Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/121/07/66/6382341/me-1999-jul8.pdf by guest on 25 September 2021 produced electricity directly from a chemical reaction be­ tween two different m etals. Static electricity batteries such as the Leyden jar had provided o nly sudden electric pulses during discharge. For the first time, investiga tors could draw a continuous electric current fo r hours, instead of relying on an erratic spark in a Leyden jar. In 1820, the D anish experi­ menter H ans O ersted showed that Franklin had been half­ wrong in his conclusion tha t electricity and m agn etism were unrelated. O ersted ob­ served that the needle of a nea rby compass moved when he closed the circuit through a wire and battery. This demon­ st ra te d that electricity was ca using m agnetism. Andre­ Davenport's model of an electric "train." The circular track is 4 feet in diameter. Power was supplied from a M arie Ampere in France soon stationary battery to the moving electric locomotive, using the rails as conductors for the electricity. showed that the magneti c ef­ fec t could be multiplied by coiling the w ire. William circuits around a soft iron core that he procured from Sturgeon went the next step in 1825 by wrapping an the Crown Point Iron Works, the company for which uninsulated coil of wire aro und an insulated horseshoe­ he eventually designed the m achine that used his ore­ shaped iron core, thus making the fi rs t electromagnet, separating electrom agnet. which lifted about 5 lbs. T he iron separation technique developed by H enry N ow that it was shown that electricity could produce was, in a sense, the magnetic equi va lent of the cotton m agnetism , the reverse qu es ti on arose: w hether m ag­ gin. That device, invented in 1794 by Eli Whitney, used netism could produce electricity. T he first attempts spikes on a ro tating drum to comb the seed from the consisted of holding a magnet near a w ire. No electric­ fiber. For the first time growing cotton was profitable, ity was observed. Then, in 1831, Michael Faraday Sll C­ because a single worker could produ ce 50 lbs. of pure ceeded in producing electricity by means of magnetism cotton per day. Threshing nnchines were being built on when he move d a disc perpendicular to a m agnetic a similar principle. T he ancient p rocess of beating the fi eld. Almost simultaneously, ] oseph H enry, inventor of wheat with a wooden flail to separate the grain from the the ore- separation process that so excited D ave nport, chaff was to be replaced by spikes on a rotating drum . used a 1T1Ore powerful lifting magnet of his own design to show that electricity could be produced from mag­ DAVENPORT INVENTS THE MOTOR netism by changing the strength of the magnet. Soon after he learned of the H enry magnet, Davenport T he discovery that magnetism could ca use electricity traveled the 25 miles to Crown Point on a horse to wit­ was a vital step toward the m odern electric world. T he ness the wonders of magnetic lifting power. The amazing only previously demonstrated techniques for producing sight further inflamed his interest. H e decided to travel elec tricity had been the limited-potential static electric another 80 miles south, to Albany, to meet H enry, only MEC H AN ICA L ENG IN EE R I NG JULY 1999 67 to find out that he had moved down to Princeton. to one of the magnets he could get the rotor to com­ Returning home out of money, D ave nport called upon plete another half- turn. Davenport then devise d what his brother, a peddler, to join him with his cart for an­ we now call a brush and commutato r. Fixed wires from other trip to C row n Point. Once there, they auctioned the fram.e supplied current to a segm.ented conductor the brother's products and traded a good horse for an in­ that supplied current to the rotor-mounted electromag­ ferior one to obtain money to buy the magnet. When net. T his provided an automatic reversal of the polarity they got hom e, the brother suggested trying to recover of the rotor-mounted magnet tw ice per rotati on, re­ the cost by exhibiting the magnet for a fee. sulting in continuous rotation. Thomas D avenport had other plans . H e unwound and The motor had the potential to drive some of the dismantled the magnet as his wife, Emily, took notes on equipment in D avenport's shop, but he had even bigger Davenport traveled 25 miles to Crown Point on a horse Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/121/07/66/6382341/me-1999-jul8.pdf by guest on 25 September 2021 to witness the wonders of magnetic lifting power. its method of construction. H e then started his own ex­ ideas. The era of the steam locomotive and railroa ds was periments and built two more magnets of his own de­ j ust beginning, but already boiler failures and explosions sign.