Granville Woods and Induction Telegraphy

EDITORIAL NOTE: Each year February is Black History Month, but this year we will also mark the 50th anniversary of the Civil Rights Act of 1964. With this in mind we decided to do a series celebrating the important and innovative contributions of African-Americans. This article is the continuation of The Black Edison: Granville WoodsMr. Guttag also wrote God’s Scientist: George Washington Carver as a part of this series. Later this month we also will take a look at recent innovations coming out of historically black colleges and universities. For more on this topic please visit black inventors on


Granville Woods, circa 1887.

Now we come to what I consider the “fun” part of this article:  Granville Woods’ inventions and patents.  There are some who say that the number of patents Woods obtained is at least 60, may be even much higher.  But from Professor Fouché’s book, I’ve only identified 45 patents for Woods which is still a pretty awesome figure.  These patents may be divided into essentially 4 technology categories:  (1) induction telegraphy of which there are 8 patents; (2) electrical railways of which there are 20 patents; (3) other electrical devices of which there are 13 patents; and (4) 4 patents on “other inventions” that don’t fall into any specific category.

I’m going to address in this article only the first category of inventions, induction telegraphy, for which Woods is most famous for.  So why is induction telegraphy important?  Well, here’s a hypothetical problem, one that Woods would understand quite well:  A train station needs to communicate with train #1 to prevent a collision with train #2 heading towards train #1.  (By the way, like Woods, I’m very fond of trains and railroads.)  If the train station doesn’t communicate with train #1 about this impending collision with train #2, you might get the unfortunate scenario shown in the illustration above: the dreaded telescoping train crash.  What you see here is the “head-on” variety of such a crash, but an even more deadly version may occur when a following train crashes into the rear of another slower or stationary train.  So if we want to avoid this “bad boy” of train crashes, our train station has got to communicate with train #1 and quickly.

But we’ve got a challenge:  how does the train station communicate with train #1 if there’s no direct telegraph line connection?  It simply isn’t practical to reel out telegraph line from the station as train #1 continues moving away.  So what’s the solution to no direct telegraph connection?  Here’s Granville Woods’ ingenious solution:  by using induction telegraphy, we can communicate without a direct telegraphic connection between the station and train #1.

So how does induction telegraphy work?  And here’s my first question:  how many of you are mystified and even terrified by how electricity and magnetism work?  Well, you’re not alone.  As an undergraduate chemistry major, I found electricity and magnetism in my introductory physics class to be a daunting subject.  About all I remember from that class is a variant of what’s called the “right-hand rule” for determining in which direction the magnetic force goes.  Or what we called “turning V, the charge velocity, or as others refer to it, I, the electrical current, into B, the magnetic field.”  And the direction that my thumb (which you can’t see) is now pointing is F, the direction of the magnetic force.  Does that sound familiar to any of you?

To understand how induction telegraphy works, we’re going to need to understand three areas involving electricity and magnetism:  (1) electromagnetic induction; (2) coupled inductors; and (3) electrical telegraphs.  Once we learn how these three areas work, we can then put them together to understand the true genius of how Wood’s railway induction telegraphy invention works so our train #1 hopefully doesn’t cause a telescoping train crash with train #2.


Electromagnetic Induction

First, let’s talk about electromagnetic induction.  The relationship between electricity and magnetism which causes electromagnetic induction wasn’t known until around 1830, primarily through the efforts of the famous British physicist, Michael Faraday.  Woods’ application of electromagnetic induction to induction telegraphy occurred about 50 years after Faraday’s discovery.  Basically, the first component of Wood’s induction telegraphy is an electromagnet or inductor.  Most inductors include a metal core, as well as wire coil or winding surrounding the core.  The passage of electrical current through the winding creates or induces a magnetic field which is intensified by the metal core.


Coupled Inductors

The second component of Woods’ induction telegraphy is to use two of these inductors in combination to form coupled inductors.  A modern day example of coupled inductors is a power transformer.  In coupled conductors, we have an inductor #1 with its respective winding, and an adjacent inductor #2 with its respective winding.  Each winding of inductors #1 and #2 also surrounds a metal core.  Because inductors #1 and #2 are adjacent or coupled to each other, there is now a zone of mutual inductance.  For example, as electrical current flows through the winding of inductor #1, it creates a magnetic field which then causes or induces electrical current to flow through the winding of inductor #2, and vice versa.


Electrical Telegraph

The third and final component of Woods’ induction telegraphy requires a mechanism for using the coupled inductors to transmit, as well as receive, an electrical communication signal.  That’s where the electrical telegraph comes in which was invented by Samuel Morse around 1840.

So how does an electrical telegraph work?  The electrical telegraph also has essentially three components.  The first is a telegraph key which generates the electrical signal.  The second component is a telegraph sounder which receives and responds to those transmitted signals.  The third component is a telegraph wire over which the signals generated by the telegraph key are transmitted to the telegraph sounder.

When the lever of the telegraph key is pressed down, an electrical circuit is formed, thus generating an electrical signal.  The patterned movement of this lever down and up causes the telegraph key to generate a pattern of short (dots) and long (dashes) or signals, (i.e., Morse code), and also corresponding to the various letters of the alphabet.  This pattern of signals is then transmitted over the telegraph wire to the telegraph sounder.  In synchronous response, the telegraph sounder then “clicks,” when it receives a signal, and “clacks,” when it no longer receives a signal, thus audibly repeating the pattern of transmitted signals, and letters generated, by the telegraph key.  That, in a nutshell, is how an electrical telegraph works.


Wood’s Railway Induction Telegraphy

So let’s now combine what we’ve learned about electromagnetic induction, coupled inductors, and the electrical telegraph, just as Granville Woods did about 130 years ago, to create railway induction telegraphy and save our train #1 from a potentially deadly telescoping train crash with train #2. 

To illustrate the electromagnetic induction and coupled inductor components, we’ll use Woods’ U.S. Pat. No. 373,915, and particularly two drawing figures from the ‘915 patent which illustrate induction telegraphy between the bottom of a train car and a telegraph wire carried between the railroad tracks.  Woods also invented an improved version of railway induction telegraphy which became U.S. Pat. No. 373,383 and for which Woods was inducted into the National Inventors Hall of Fame in 2006.  The invention in the ‘383 patent involves inductive transmission between overhead telegraph wires and the roof of the train car.  But we’re going to use the earlier version of Woods’ induction telegraphy described in the ‘915 patent because it’s much easier to understand from the drawings of this patent how the electromagnetic induction and coupled inductor components work in induction telegraphy.

As shown in FIG. 2 of the ‘915 patent, Wood’s railway induction telegraphy has an inductor #1, identified as C4, which is a circular loop of core wire surrounded by a helical winding.  Wood’s railway induction telegraphy also has an inductor #2, identified as B-B in FIG. 2, which is also formed from another core wire surrounded by another helical winding.  Because inductors C4 and B-B are adjacent, they form coupled inductors having a zone of mutual inductance.

To add the third component, the electrical telegraph (and in some embodiments of Woods’ railway induction telegraphy, telephonic signals), we’ll use FIG. 4 from Woods’ ‘915 patent.  Again, we have inductor #1, identified as C in FIG. 4., which is mounted on our moving train.  We also have inductor #2, identified as B-B in FIG. 4, which is mounted between the railroad tracks and over which passes inductor #1 or C.  Again, because inductor C mounted on the train passes over and is adjacent to inductor B-B, we again have coupled conductors, as well as a zone of mutual inductance.

As also shown in FIG. 4, inductor C is directly connected to the train’s transmitter-receiver system A-A’ (which may be either an electrical telegraph or telephone system), while inductor B-B is directly connected to the station’s transmitter-receiver system through a telegraph (or telephone) wire.  By sending a series of telegraphic or telephonic electrical signals from the station’s transmitter system, those signals are passed, by inductor B-B, through the zone of mutual inductance to inductor C, which then passes those signals onto the train’s receiver system.  In similar, and reverse fashion, the train’s transmitter system may also send signals to the station’s receiver system, all without a direct telegraphic or telephonic connection between the train and the station.  With this ability to communicate with a moving train, our train station can now alert train #1 and avoid a potentially disastrous and deadly telescoping train crash with oncoming train #2.


Final Thoughts on Woods, the Inventor

So where does Granville Woods fit into the pantheon of inventors?  Professor Fouché is correct that we’ve got to be careful in creating myths about black inventors like Woods, and thus turning them into “gods.”  But Woods certainly holds his own against any American inventor, black or white.

Besides Woods’ prolific number of inventions, here is some other information to consider.  In 1887, the Cincinnati Catholic Tribune called Woods the “greatest electrician in the world.”  That statement is a bit of a stretch, but it is probably accurate to say that Woods was certainly one of the greatest American inventors in the electrical field.

As noted earlier, in the period from 1900 to 1910, many of Woods’ patents were assigned to the two largest existing corporations providing electrical power in America, General Electric and Westinghouse.  That mega corporations like these recognized the value of what Woods invented, and potentially even in spite of the fact that he was black, speaks volumes about Woods inventive achievements.

In 1917, the Journal of Negro History said that there was “no inventor of the [black] race whose creative genius ha[d] covered quite so wide a field.”  Now this statement may have been written before the significant achievements by George Washington Carver, another black inventive giant in the field of peanut chemistry, were widely recognized.  (We’ll hear more about Carver in my second article.)  Even so, by the early 20th Century, the significant inventive accomplishments of Woods, at least as a black inventor, were being recognized and saluted.

In 2006 (and after Carver was inducted as the first black inventor in 1990), Woods was inducted, along with Lewis Latimer, (one of the other contemporary black inventors I mentioned earlier), as the 2nd or 3rd black inventor into the National Inventors Hall of Fame.  When you are inducted by a national organization which recognizes, honors, and encourages inventive achievement, and which has also inducted the likes of Thomas Edison, it’s very hard to dispute that Woods has now reached the summit of recognition for inventive achievement.

In conclusion, with the possible of exception of George Washington Carver, there is simply no other parallel to Granville Woods amongst black inventors.  In my view, calling Woods “The Black Edison” also doesn’t demean him or his accomplishments, but, instead, recognizes his outstanding creativity and genius.  Frankly, that title says that Woods rightly belongs in the category of the inventive elite that includes Edison.  And Woods’ prolific inventive achievements in a field of technology that many, including me, consider daunting, certainly entitles him to be considered one of the inventive titans, be they black or white.


*© Eric W. Guttag 2012, 2014.  (Based on a presentation made in February 2012 at the West Chester Library, West Chester, Ohio.)



Warning & Disclaimer: The pages, articles and comments on do not constitute legal advice, nor do they create any attorney-client relationship. The articles published express the personal opinion and views of the author as of the time of publication and should not be attributed to the author’s employer, clients or the sponsors of

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