How A Bored Math Teacher Invented the Telegraph

Why would a math teacher named Joseph Henry invent the telegraph? And didn’t Samuel Morse invent the telegraph? Well, I’ll tell you and along the way I will talk about a transformative book, the importance of insulating wire, dropping thousands of pounds of weights for fun, the first doorbell, a black assistant named Sam Parker, and why he couldn’t get published or get a patent if he wanted to, and one really big missed opportunity. Ready? Let’s go.

[a bar of iron with 9 separate coils of wire that he could connect individually or combined to the same battery.  ]

Henry came up with the idea of first wrapping the wire with silk (made from strips of his wife’s petticoats), making the first insulated wire.  With bare wire, the wires could not touch or the system would short circuit (jump between wires instead of going through the wires). [Insulating wire allowed Henry to wrap the iron very tightly together, which vastly increased the magnetic field from the wires which makes a significantly stronger electromagnet.  At first, Henry did get a far stronger magnet with more coils of wire.] 

Joseph Henry
Joseph Henry

Joseph Henry had a hard life.  He was born in the backwoods of Albany, New York in 1797 to poor Scottish immigrants.  His father was a notorious drunk who died from drink when Henry was just nine years old.  Henry then dropped out of school and worked as an apprentice for a watchmaker but after a couple of years, the watchmaker went out of business.  He then took odd jobs and dreamed of being an actor while his mother took in boarders.  One boarder loaned the 16-year-old Henry a book on science that inspired him to, “devote my life to the acquisition of knowledge”.

When Henry was 19, he received a full scholarship to further his education at a high school called the Academy.  He studied Mathematics, Physics, and Chemistry and supplemented his income with tutoring.  He had a series of unrelated jobs and by 1826 he got a job as a Math teacher at the same school he went to ten years earlier.  At first, Henry was glad of the offer to work at the “Academy”. However, Henry really wanted to do research and quickly felt irritated spending half his time with the “drudgery” of teaching algebra.

Then, one day, he read a paper about how an Englishman named William Sturgeon had made a magnet with electricity by wrapping wires around a soft iron bar.  Henry decided to use this method to make the strongest magnet he could with a single simple battery.  Henry came up with the idea of first wrapping the wire with silk (made from strips of his wife’s petticoats), making the first insulated wire, which allowed him to wrap the wire as tightly as he could around a metal bar.  Tightly winding wires makes a significantly stronger electromagnet.  Before Henry, they didn’t have any insulated wires so the wires could never touch.  At first, Henry got a much stronger magnet with more coils of wire.  However, after a while, adding more wire didn’t make the magnet stronger, it made it weaker.  Henry realized that the battery was producing less and less current when he used a long wire (the longer the wire the more resistance it had).  Henry then got the idea of wrapping a bar of iron with 9 separate coils of wire that he could connect individually or combined to the same battery.  He then experimented with attaching different sections of the magnet to a simple battery (just zinc cylinders with copper in a half a pint of acid).  He put a scale under the magnet and measured the maximum weight it could support.  If only one coil was electrified then it could support 7 pounds.  If, however, he attached two to the same battery in what we now call parallel (so that the current goes through both coils at the same time), he could get the magnet to hold up 145 pounds.  If he attached all nine coils he managed to lift 650 pounds!  Soon, Henry bested his own invention and made a magnet that held over 2,000 pounds.  One of his favorite demonstrations was to lift a very heavy object, then remove the battery and have it fall down with what must have been a terrifying bang, which, according to Henry, “never fails to produce a great sensation among the audience as before the fall they can scarcely believe that the magnet supports the weight.” 


Henry wondered how far he could separate the battery and the electromagnet.  First, he scaled down his experiment and made a simple electromagnet that was tightly wound with insulated wire and was placed near a metal bar on a pivot.  When the electromagnet was electrified, it moved the bar which rung a bell.  Basically, it was the first… doorbell.  He then spooled out wire throughout the upper rooms of the Academy and managed to make the bell ring with a signal from a battery over a mile away.  More than a doorbell, Henry had invented the telegraph. 

Amazingly, Joseph Henry recognized that he had invented the telegraph at the time.  See, people had been trying to use electricity to send information long distances since the 1700s.  By 1820, a Danish man named Oersted had determined that a current in a wire would cause a nearby compass needle to turn.  After Oersted, multiple people attempted to use this fact to transmit signals long distance, a system that they called the electric telegraph.  When Sturgeon coiled wire around an iron bar to make the first electromagnet in 1824, his friend and mentor Peter Barlow tried to use it to make an electromagnetic telegraph but found it didn’t work more than 200 feet and gave it up.  Therefore, when Henry made his more powerful electromagnet and long-distance communication in 1831, he added that it is, “directly applicable to Mr. Barlow’s project of forming an electro-magnetic telegraph” 

Henry’s publication in 1831 won him acclaim and he was offered a job working as a professor at Princeton University the very next year despite the fact that he admitted that he was not “a graduate of any college”.

At Princeton, Joseph Henry built a combination of both his bell ringing and his heavy lifting demonstrations.  He had a battery connected for miles to a small coil.  Instead of the coil ringing a bell, the coil pulled a switch that closed a circuit with another battery that was next to a large electromagnet.  In this way, Henry could remotely lift and drop an astonishing weight from a large distance.  Joseph Henry had not only invented the telegraph, but he had also invented the relay, an electromagnetic switch that would connect a new circuit that could extend the telegraph for as long as one wanted to.    

electro-magnetic telegraph
electro-magnetic telegraph

The next year Henry also installed a telegraph where he draped wires on trees between his laboratory and his house to tell his wife when he wanted lunch.  He used a single wire and then grounded the other end for the return passage.  This is the first time that the Earth was used as a conductor for a telegraph – an important feature for long-distance telegraphs[i].  

Henry’s work was greatly aided when he was assigned an assistant: a free black man named Sam Parker.  Parker was a bit of a campus character, he was known to sneak in late-night dinners to local students for old suits and was rumored to own over a hundred suits of clothes that he changed multiple times a day.  Henry wrote often of his appreciation for Parker’s work and said he was indispensable.  For example, in 1842, Henry wrote that his work was delayed for two weeks because Parker was sick.  However, like most white people at the time, often treated his assistant like a child, and although anti-slavery, Henry would be considered racist by today’s standards.  

The students were even more racist.  They loved to see Parker do electrical experiments but it was a dangerous time to be black in America, especially one that was known to “put on airs”.  We only know about Parker through a few comments in Henry’s papers and the autobiography of a Princeton graduate named Edward Shippen (whose picture we have of course).  Shippen described how Parker was considered by the students to be “one of the most important persons in Princeton,” while he also described how he (and fellow students) disliked Parker’s independence or “impudence”.  Years later Shippen gleefully and maliciously described how Parker’s behavior “improved” when Parker was (and these are Shippen’s words) “thoroughly flailed by a stalwart north Jerseyman.”

Henry never patented his ideas on the telegraph.  His friends actually encouraged him to do so as early as 1831 but he decided it was incompatible with “the dignity of science[ii]” to do so.  Or at least that is what he said years later once she realized how powerful, influential, and financially successful the telegraph would be.  Sam Parker never patented anything either, but for different reasons.  First, it is unclear exactly what Parker discovered, as no scientific journal at the time would publish the research of a black servant/assistant.  Also, even if he did try to patent these ideas he could never have afforded the $30 patent fee as he only earned $48 a year!  Instead, the patent and the money and fame of the telegraph went to a truly loathsome person, Samuel Morse of the Morse code.

[i] P 35 “Joseph Henry’s House and Campus Plan” Tjung et all

[ii] p 150 “A Memorial of Joseph Henry” Joseph Henry

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