Any student of electromagnetics knows the story – Michael Faraday devised the ingenious concept that electric and magnetic effects were due to “fields” pervading space. Applying this simple concept, he was able to devise and demonstrate the phenomenon of induction, discovering the physics that gives rise to electric motors and generators. Faraday’s fundamental insight inspired James Clerk Maxwell who, a generation later, cast Faraday’s nebulous field conception in rigorous mathematical form. By so doing, Maxwell predicted the existence of electromagnetic waves – the properties of which Hertz established and proved yet another generation later.
As usual, there’s more to the story.
One hundred eighty years ago today, on March 12, 1832, Faraday wrote a secret letter predicting the existence of electromagnetic waves. Faraday submitted his letter to the Secretary of the Royal Society of London where it lay for over a century in a strong box. The letter only came to light when it was opened by Sir William Bragg on June 24, 1937. The only online publication of this letter in its entirety appears to be in Google Book results such as for Garratt’s The Early History of Radio, the text in which I found it, or in journal articles behind pay walls. Faraday’s magnificent foresight deserves more attention than it has thus far received, so I’m delighted to share Faraday’s letter in full, after the break.
March 12, 1832
Certain of the results of the investigations which are embodied in the two papers entitled ‘Experimental Researches in Electricity’ lately read to the Royal Society, and the views arising therefrom, in connexion with other views and experiments lead me to believe that magnetic action is progressive, and requires time, i.e. that when a magnet acts upon a distant magnet or piece of iron, the influencing cause (which I may for the moment call magnetism) proceeds gradually from the magnetic bodies, and requires time for its transmission, which will probably be found to be very sensible.
I think also, that I see reason for supposing that electric induction (of tension) is also performed in a similar progressive way.
I am inclined to compare the diffusion of magnetic forces from a magnetic pole to the vibrations upon the surface of disturbed water, or those of air in the phenomenon of sound; i.e. I am inclined to think the vibratory theory will apply to these phenomena as it does to sound, and most probably to light.
By analogy, I think it may possibly apply to the phenomenon of induction of electricity of tension also.
These views I wish to work out experimentally; but as much of my time is engaged in the duties of my office, and as the experiments will therefore be prolonged, and may in their course be subject to the observation of others, I wish, by depositing this paper in the care of the Royal Society, to take possession as it were of a certain date; and so have right, if they are confirmed by experiment, to claim credit for the views at that date; at which time as far as I know, no one is conscious of or can claim them but myself.
It would be altogether wrong to attach too much historical significance to this fascinating document or, for example, to regard Farday as the prime inventor of radio on the grounds that it refers to wave propagation. Nevertheless, in light of Faraday’s later contribution to what has become known as field theory, one may at least remark on the fact that knowledge of the propagation of electromagnetic waves can now be traced to these ‘Original Views’ which Faraday deposited with the Royal Society in 1832.
Garratt is correct that Faraday’s insight, hidden as it was for over a century, is of little historical significance in the ultimate discovery of Maxwellian electromagnetics and radio technology. The great significance of this letter is what it tells us of Faraday’s genius and the largely forgotten revolution he wrought in human thought.
Before Faraday, physicists thought in terms of mathematical relationships governing physical behavior through instantaneous action-at-a-distance. Faraday’s key insight was that effects have physical causes and these causes can be described as fields permeating throughout space. Although it would await the genius of James Clerk Maxwell to mathematically describe Faraday’s conception, Faraday’s forgotten letter shows that he foresaw the complete picture of fields evolving and propagating across space at least a decade before any of his contemporaries. Faraday’s 1844 paper, “Thoughts on Ray Vibrations,” lays out his more developed thinking on the matter.
I am indebted to Gerald Garratt (1906-1989), author of The Early History of Radio: From Faraday to Marconi (I E E History of Technology Series) for his presentation of this fascinating footnote to electromagnetic history. Garratt was especially interested in the work of Heinrich Hertz, and his friendship with Frau Hertz, who fled Nazi Germany for Britain in 1936, enabled him to acquire some of Hertz’s original manuscripts for the museum at which he was employed. He wrote Early History of Radio from the perspective of a passionate technologist eager and able to fill in the gaps of the standard historical treatments. Garratt’s work offers many unique insights I’ve found nowhere else.
2 thoughts on “Faraday’s Secret 1832 Letter Reveals Electromagnetic Waves Prediction”
Very interesting piece, thanks for finding and reporting it! Written at a later date, I do remember reading something about Faraday suggesting that the vibrations were likely the cause of light. Also, what Maxwell focused on was Faraday’s “electrotonic state”, and magnetic phenomena were results of changes in the state (stress, etc.) state of that field. Maxwell called that field “electromagnetic momentum” (because the time derivative equals force, just like with mechanical momentum) and is today called magnetic vector potential, which JCM viewed as primary and used the symbol “A”. Magnetic field was secondary and JCM used the symbol “B” (but I wonder if Ampere had something to do with that…). Heaviside dumped the potentials and put everything in terms of E and H. Faraday definitely introduced the qualitative concept of a field, but I don’t know (my ignorance) if he can be credited with the concept of the electric and magnetic field. If anyone has some insight there, would be good to hear.