From Immigrant to Inventor

by Michael Pupin

Faraday claimed that all electrical and magnetic actions are transmitted from point to point along his lines of force; and, impelled by a remarkable intuition, he insisted that his lines of force are not mere geometrical pictures but that they had a real physical existence, and that there was something like muscular tension along these lines of force tending to contract them, and a pressure perpendicular to them tending to expand them; and that these tensions and pressures give the same numerical value for the mechanical force between the charges as that calculated from Coulomb’s law, but with the fundamental difference, which Faraday pointed out, that his hypothesis demands a definite finite time for the transmission of electrical and magnetic forces; whereas according to the hypothesis of direct action at a distance, which Coulomb’s law neither favors nor opposes, these forces are transmitted instantaneously. The question of the velocity of transmission of electrical and of magnetic forces through space became, therefore, a crucial question in the decision between the old view and Faraday’s view.

In a letter addressed to Maxwell in 1857, and quoted by Campbell, Faraday said:

I hope this summer to make some experiments on the time of magnetic action ... that may help the subject on. The time must probably be short as the time of light; but the greatness of the result, if affirmative, makes me not despair. Perhaps I had better have said nothing about it, for I am often long in realizing my intentions, and a failing memory is against me.

This letter was written ten years before Faraday’s death, and nothing was ever reported about the result of the experiment planned by him. We know, however, that the result which he expected from the experiment was obtained thirty years later by Hertz, a pupil of Helmholtz.

I imagined at Arran that I could hear Faraday say:

Where the lines of magnetic force are there is magnetism, and where the lines of electric force are there is electricity.

Faraday’s answer to the questions, “What is electricity?” and, “What is magnetism?” was, therefore, according to my understanding at that time, that they were manifestations of force; and where these manifestations exist there is electricity and there is magnetism, in the sense that there are pressures and tensions which are the result of a certain state of the space which may be called the electrical or the magnetic state. Faraday’s visions, as I found them nearly forty years ago, disclosed in his “Experimental Researches in Electricity,” went even so far as to suggest that matter itself consists of centres of force with lines of force proceeding from these centres in every direction to infinite distances, and where these lines are there is the body; in other words, every material body, like every electrical and every magnetic charge, extends to infinity by means of its lines of force; and hence all material bodies are in contact, explicitly denying the existence of ether. No mortal man ever suggested a bolder conception! And yet to-day we know that a conception regarding the structure of matter very similar to that first conceived by Faraday is rapidly gaining universal recognition, not merely as a new metaphysical speculation but as the logical and inexorable demand of experiment. But when Faraday told me all these strange things as I listened attentively on the slope of Goat Fell Mountain at Arran, I could not see anything in them except geometrical pictures and a lot of what appeared to me like pure metaphysics in the background of simple geometrical structures. Although I was sure that Faraday’s metaphysics had some definite physics back of it, I was unable to disentangle it from the hypothetical notions which I did not understand clearly. Maxwell, I thought, must have disentangled that physics, and I often thought of my Scotch friend at Arran who asked me the question: “Can you see in Faraday as far as Maxwell, the Scotchman, saw?”

When I came to Berlin my head was full of Faraday’s lines of force starting at electrical and magnetic charges and winding in all sorts of shapes through space, like stream lines which start from the sources of a river and follow it in its flow toward the ocean. The physical facts and principles which Faraday discovered stood out sharply defined like the bright stars in the firmament of a clear and quiescent summer night; but the conception of the new view of attracting and repelling electric and magnetic forces, which he represented graphically by his lines of force, endowed with strange physical powers residing in pressures and tensions, left in my mind impressions which made me feel that my faith in the new doctrine was not very strong. Faith without conviction is a house built upon sand. Helmholtz said once:

I know too well how often I sat staring hopelessly at his descriptions of the lines of force, their number and their tensions.

Little I thought during my journey from Arran to Berlin in October, 1885, that two years later all the nebulous notions in my perplexed mind would lift like the mist before the early rays of a sunny autumn morning. I continued my studies of Faraday during my first year in Berlin, reserving for that purpose the necessary time for extra reading. What did the physicists of Berlin think, I wondered, of Faraday’s tubes or lines of force?