From Immigrant to Inventor

by Michael Pupin

The gradual development of this view was due to the gradual development of new physical concepts which were born in Faraday’s mind and existed there as a poetical vision; but in Maxwell’s mind they appeared as physical quantities having definite quantitative relations to other well-known physical quantities, which a physicist can measure in his laboratory. In every creative physicist there is hidden a metaphysicist and a poet; but the physicist is less apt to persist in his occasional errors as metaphysicist and poet, because the creations of his speculative mind and of his poetical vision can be subjected to crucial experimental tests.

Faraday’s “Experimental Researches in Electricity,” published in three thick volumes, looked like very long reading. But my studies at Arran soon convinced me that no reading is long which continually stirs up the interest of the eager reader. Faraday was a pioneer in science, and the descriptions of his explorations read like tales from a new world of physical phenomena, full of poetical visions which his discoveries suggested to his imagination. It must be said, however, that in spite of his wonderful imagination and his free use of it, no investigator ever succeeded better than Faraday in drawing a sharp line of division between the new facts and principles which he had discovered and the visions which his imagination saw in the still unexplored background of his discoveries. For instance, his discovery that a perfectly definite and invariable quantity of electricity is, as we express it to-day, attached to every valency of an atom and molecule, expresses a physical law which his experiments revealed and which he illuminated with all the light of his brilliant intellect. But when this new and precious morsel of the eternal truth had been disclosed by his experiments, then Faraday the scientist stepped aside, and Faraday the poet disclosed his visions about the constitution of matter suggested by what I called at Arran the atomic distribution of electricity in material bodies.

A man who discovers one of the most remarkable facts in modern science, namely, that in every atom and molecule there are definite and equal quantities of positive and negative electricity, and that the forces between these electricities are by far the largest known forces which keep together the components of chemical structures, cannot, if he has the imagination of a discoverer, refrain from asking the question: “What is matter?” The reader of Faraday’s “Experimental Researches in Electricity” rejoices whenever Faraday, the poet and prophet, asks an apparently speculative question of this kind, because he knows that he will be thrilled by the poetical fancy which dictates Faraday’s answer. Faraday’s new facts and principles revealed by experiment are steeped in the honey of his fancy; they are rich food made delicious by the flavor of his poetical imagination, even when that flavor leaves the ordinary mortal guessing as to its exact meaning.

Two other questions Faraday often approached in these researches; they may be stated as follows: What is electricity? and, What is magnetism? He discovered that motion of magnetism produces electrical forces in a manner similar to that in which, according to Oerstedt’s discovery, motion of electricity produces magnetic forces. This remarkable reciprocal relation between electricity and magnetism stirs up the imagination, and makes it eager to look behind the curtain which separates the region of the revealed truth from that which is still unrevealed. It was undoubtedly this eagerness of the explorer which encouraged Faraday to approach the questions, What is electricity? and, What is magnetism? Faraday never gave a final answer to these questions, but his magnificent efforts to find this answer gave birth to new ideas which are the foundation of our modern electromagnetic view of physical forces. One of the great pleasures of my life has been the contemplation of the gradual unfolding of this new view; and if in the course of this simple narrative I succeed in describing some of its beauties, I shall consider that this narrative was not written in vain.

Since, as explicitly stated by Faraday, electricity and magnetism are known by the forces, only, which they exert, it was plain to him, as his books, “Experimental Researches in Electricity,” testify, that the first question which must be answered was the question: How are the forces between electrical charges and between magnetic charges transmitted through the intervening space—the same way as gravitational forces, or are they transmitted in a different way? In his unceasing efforts to answer this question Faraday made a radical and fundamental departure from the view of the natural philosophers of his time. He stood alone and devoted a very large part of his experimental work and of his philosophical thought to the justification of his position. He stood alone for a very long time, because he was formulating a radically new physical concept which the world knows now to be one of the most fundamental concepts of the electromagnetic science of to-day; and it was difficult for his contemporaries and for his students of forty years ago, including myself, to understand him. In an address on Faraday by Helmholtz, which I read during my student days in Berlin, the following sentence refers to Faraday’s difficulty just mentioned:

It is generally very difficult to define by a general statement a new abstraction, so that no misunderstandings of any kind can arise. The originator of a new concept of that kind finds, as a rule, that it is much more difficult to find out why other people do not understand him than it was to discover the new truths.

It was very consoling to me to find out in Berlin from no less an authority than Helmholtz that I was not the only poor mortal who was guessing in vain about the exact meaning of Faraday’s visions.

Newton’s law of gravitation enables the astronomers to calculate accurately from a simple mathematical formula the motion of celestial bodies, without any assumption concerning the mechanism by which gravitational force is transmitted from one body to another body at a distance, say, from the sun to the earth. Newton’s formula says nothing about the time of transmission. The action can be assumed to be direct action at a distance and therefore instantaneous. Experience seemed to indicate that this assumption is correct, because no detectable errors are committed when one assumes that gravitational force travels with infinite velocity. Faraday refused to accept this belief in direct action at a distance for electric and magnetic forces. A few words, only, will suffice to describe how Faraday attempted to eliminate the belief in this direct action at a distance for electrical and magnetic forces. These attempts will always be recorded in history as the first steps in the development of the modern electromagnetic science.

Faraday, starting from points in the electrical and in the magnetic charges, drew numerous curves which indicated at every point in space the direction of the electric or of the magnetic force, and in that manner the whole space surrounding the charges he divided geometrically into tubular filaments which he called the lines of force. Every one of these filaments was constructed in accordance with a simple rule, so that it indicated at every point in space not only the direction but also the intensity of the force. A specific example, often employed by me at Arran, will illustrate this. A conducting sphere, say of copper or brass, is charged with positive or with negative electricity. When that charge is in equilibrium it is, as was well known, all on the surface of the sphere and uniformly distributed. Its force of attraction or repulsion, for electrical charges in the space outside of the sphere, is obviously along radii drawn from the centre of the sphere. These radii, drawn in every direction and sufficiently numerous, envelop little cones the vertices of which are at the centre of the sphere. Adjust the size of the cones in such a way that the area of the section of every one of them with the sphere is the same, and make their total number proportional to the charge on the sphere. These little cones are then in this particular case the Faraday lines of force, because their direction gives the direction of the electrical force, and their number per unit area of the surface of any concentric sphere is proportional to the electrical force at any point of the surface of this concentric sphere. According to this picture there are attached to each little element of the total charge a definite number of these conical filaments or lines of force, and each element of the charge on the sphere is nothing more than the terminal of these filaments. When the charge on the sphere is increased or diminished the number of these filaments is also increased or diminished proportionately, and therefore they are more densely or less densely packed in the space which they occupy.

Should the charge on the sphere be set in motion, then the filaments or lines of force attached to it would also move. Thus far I followed Faraday, but went no farther; if I had gone just a little farther I should have met Maxwell. But, unfortunately for me, this simple picture which I constructed, in order to aid my understanding of Faraday’s “Experimental Researches in Electricity” over which I pondered at Arran, suggested nothing more than a mere geometrical representation of the electrical force which the charged sphere exerts at any point in space. It conveyed no additional information which a simple mathematical formula, well-known at that time, did not convey. Additional information, however, was added by Faraday’s imagination, which introduced here what I and many other mortals at that time considered a strange hypothesis. He described the hypothesis at great length in his books, and here is a brief statement of it: