us how to take care of them, and they are good enough for us. You say
that if we improve them we would get more summer visitors, who, with
their wealth, would increase the prosperity of our town. We don’t care
for that kind of prosperity; it brings vanity and false pride into
our New England homes, which you city people carry around with you.”
Then, pointing his trembling finger at me, the old man exclaimed: “You,
particularly, are guilty of this offense; you were the first who showed
our simple people here how to swagger about this town on a horse with a
rabbit tail.”
He referred to the almost universal custom at that time of docking a
horse’s tail; the tails of my famous cobs as well as of my saddle-horse
Clipper had been docked. After this speech, I suspended my propaganda
for more up-to-date roads. Two years later, another incident occurred
which is worth relating here. Mr. Carter, a Norfolk hunter of much
local fame, had a fine pointer dog. He went to Europe one summer and
left his dog in charge of a friend. But the dog ran away, and chased
through all the woods of Norfolk, looking for his master. One day he
came to my house; he was hungry, thirsty, tired out, and perfectly
unhappy, having failed to find his master. I petted him, gave him fresh
water to drink and some food to eat, and, while he was feasting, spoke
to him and paid him many compliments on account of his affectionate
attachment to his master. After his hearty meal he fell asleep near my
feet on the piazza, and when he woke up he looked at me and seemed to
be a much happier dog. From that moment on he followed me everywhere,
running after my horse when I went out riding. One day I was cantering
slowly along the road passing old Nettleton’s house. I saw the old man
standing near the road, apparently waiting for somebody. When I was
quite near him he beckoned me to stop, which I did, and he addressed me:
“Professor, I was very severe with you two years ago at that town
meeting. But I did not know you; now I do. That dog there would not
stay with anybody in this town, but he stays with you, and he follows
you just as he followed his master. You are good to him, and the dog
knows it. I have great confidence in a dog’s judgment, and I know now
that you are a good man, just as good as any of the folks in this here
New England town.” Then, stretching out his bony hand to me, he said:
“Shake, forgive and forget, and let us be good friends. I shall never
oppose you again at our annual town meetings. What’s good for you is
good enough for me and for our little town.”
No offer of friendship was ever more welcome to me, and there never
was a friendship of which I was more proud. Before many days had
passed, the natives of Norfolk, from the illustrious Eldridge family,
the angels of the town, down to the most humble day-laborer, felt the
same toward me as old Nettleton did; that is, I always thought so, and
I have never had any reason to think otherwise. No resolution moved
by me at the annual town meetings ever failed to pass, but I always
moved slowly, and not until I was quite sure that the motion was in the
right direction. I would sooner have risked losing the good opinion of
the trustees of Columbia University than that of the good people of
Norfolk, my American Idvor. During my summer vacations in Norfolk, I
have always felt just as much at home, and as happy and contented, as I
did in my native Idvor when, during my student days in Europe, I spent
my summer vacations there. Whenever I returned to my laboratory from
my summer vacation in the bracing atmosphere of Norfolk, I have always
felt that no problem there could resist the force of my stored-up
nervous energy. That feeling early encouraged me in the belief that I
had completely recovered from the breakdown of the spring of 1896, and
this belief gave wings to every new effort.
When the news of the discovery of the Roentgen rays reached me in
December of 1895, I was busy with the research of a problem which I
had taken up in 1894, while making a foot tour in Switzerland. This is
the problem which I took up again after the recovery from the breakdown
of 1896. I must confess here that I never returned to X-ray research,
because for a long time after my illness even the sight of an X-ray
tube made me almost hysterical.
During the first half of the summer of 1894, Mrs. Pupin and I were
staying at a little hotel on Lake Wannensee in Switzerland; I was
preparing my lectures on the mathematical theory of sound. Lord
Rayleigh’s treatise called my attention to the classical problem which
ten years before I first saw in La Grange’s famous treatise. I had
bought it second-hand in Paris, and had studied it in my mother’s
garden at Idvor. The problem was a hypothetical one relating to an
imaginary and not to a real physical case. It may be stated as follows:
A string without weight is stretched like a violin string between two
fixed points; at equidistant intervals along this string are attached
equal weights, say bird-shot. The problem is, how will this string,
loaded with weights, vibrate when disturbed by an impulse? La Grange
found a beautiful solution for this historic problem, and the solution
marks the beginning of an epoch in the history of mathematical physics.
This solution enabled him to analyze mathematically the vibrations
of a violin string, one of the famous mathematical problems of the
eighteenth century. I made a bold attempt to find a solution for a more
general and less hypothetical form of this problem. I supposed that the
string itself had weight, and that it, as well as the little weights
attached to it, moved through a viscous medium. I felt intuitively
what the solution should be, and considered it of much scientific
importance. I finally found the most general mathematical solution of
this generalized problem, and the beauty of it was that it could be
stated in a very simple language. I shall state it later. The solution
was exactly what I had expected it to be, and it thrilled me more than
any work that I had ever done. I always believed that my training
in ground-signalling which the herdsman of Idvor had taught me some
twenty years before was responsible for this intuitive guess. Early
impressions, particularly those relating to novel scientific facts, are
very intense.
I was much encouraged by the thought that I was able to add very
substantially to the solution of a historic problem first solved by
famous La Grange. In order to communicate some of my joy to Mrs.
Pupin, I told her that I was ready to give up mathematical reading
for the rest of that summer, and we started on a drive through
Switzerland. That is, she drove, while I walked a good part of the
time, particularly when the carriage was moving along the zigzag roads
going up to a pass, which happens often in Switzerland drives. Making
short cuts, I met her every now and then on the up-grade parts of the
steep and winding roads, and rode with her on the down-grade. During
these walks, being alone, I pondered a great deal about my solution
of the generalized La Grangian problem. One day, while climbing up to
the Furka pass, it occurred to me that since the motion of electricity
through a wire experiences reacting forces similar to those in the
motion of the material elements in a stretched string, my generalized
solution should be applicable to the motion of electricity, and I was
immediately aware that I had made a very important invention. I tried
to convince Mrs. Pupin of it, but she said: “I will believe what you
say and will gladly congratulate you if you will promise that you
will not be absent-minded during the rest of our trip.” I promised,
but it was very difficult to live up to the promise. I never told her
how often I longed to be back in my modest laboratory in the musty
cellar under President Low’s office at Columbia College, and that too
in spite of the heavenly beauty of the views which on my walks met
me on every turn of the winding roads which lead up to the wonderful
passes of Switzerland. I was most anxious to submit my theory to an
experimental test. When our tour in Switzerland was finished I had
every detail of the proposed experimental tests worked out in my head,
and yet my good wife never accused me of being absent-minded. In less
than a year from that time I had finished my first rough test, and was
preparing for a more elaborate investigation when the discovery of the
X-ray was announced, at the very end of 1895, and I, like everybody
else, dropped everything and eagerly sought information about this
wonderful discovery. It was the work I dropped then which I took up
again after my recovery from the breakdown of 1896.
Now what is the invention which occurred to me first on my walk to the
Furka pass in Switzerland in the summer of 1894? A bit of scientific
history is connected with it, which I shall tell here briefly:
A vibrating motion of electricity at one end of a long wire is
propagated along the wire in much the same way as the vibratory motion
of a rope or string is propagated from one of its terminals to the
other. This propagation of electrical motion from one end of a long
conducting wire to the other was first investigated by Professor
William Thomson, the late Lord Kelvin, of the University of Glasgow,
in 1855, when the first Atlantic cable was projected. He worked out
the problem for electrical signalling over a submarine cable, and
three years later Kirchhoff, who was one of my teachers in Berlin,
worked it out for telegraphic signalling over land-lines stretched over
poles. When telephony was invented in 1876, there was, of course, a
demand for a mathematical theory of telephonic transmission over long
conducting wires. He who understood Thomson’s and Kirchhoff’s work
could experience no serious difficulty in working it out. Vaschy, a
Frenchman, and Heaviside, an Englishman, were the first to work it out;
they did it in the chronological order just indicated, Vaschy leading
Heaviside by about two years. They both observed that just as in cable
and land-line telegraphy so also in telephony the reduction of the
transmitted electrical force was the smaller the larger the so-called
inductance of the transmitting wire. Many people believe that this
observation was an important discovery; I never thought so, because
I believed that Thomson’s and Kirchhoff’s work made that observation
obvious. But, however that may be, the observation was made by Vaschy
two years before it was made by Heaviside, and neither one nor the
other saw in it a special case of a general physical principle, which
the Allies appreciated much during the World War in their struggles
against the submarines. I shall describe it briefly:
Sound is transmitted through water or through a solid much more
efficiently than it is through air. I knew that, when, as herdsman’s
assistant in Idvor, I learned the art of signalling through the ground.
Now why should water or hard and heavy ground transmit sound better
than air does? Idvor’s herdsman did not tell me that, but, having
gained the knowledge of the fact very early, I was prepared to seize
upon the dynamical explanation as soon as I needed it; and I felt the
need of it in Switzerland in the summer of 1894.
Transmission of sound means transmission of vibratory motion from
one element of a substance to the contiguous elements. The element
which transmits its vibratory energy acts and the elements which
receive it react. Each element is capable of exerting three reacting
forces. One is against the change of velocity of its motion, that
is, against change of momentum. This reaction is called the kinetic
reaction, and, as I have pointed out before, it was discovered by
Galileo three hundred years ago. The second reaction is against the
elastic compression of the receiving element. It is called the elastic
reaction, and was discovered by Hook, a contemporary of Newton, two
hundred years ago. The third is a frictional reaction, the knowledge
of which is very old. There are, therefore, three forms of energy
generated in the reacting element of every vibrating body by the work
of the acting element. The first reaction results in energy of motion
of the mass of the reacting element; the second one results in the
energy of its elastic compression; and the third one generates heat.
The first and the second are energies of sound vibration and are
transmitted again to the contiguous elements, but the third is not a
vibratory sound energy and is not transmitted as such; it remains as
heat and represents the reduction of sound energy transmitted from any
one part to the contiguous parts. It is obvious that this reduction
will be, relatively, the smaller the greater the first two reactions
are in comparison with the frictional reaction. Heavy, incompressible
bodies, like water, metals, or hard solid ground, have incomparably
greater kinetic and elastic reactions than air, hence they transmit
sound much better than air does. This physical principle did splendid
service during the World War in submarine and subterranean detection by
sound. The herdsman’s assistants in Idvor, when I was a boy, profited
much from it in their signalling through the ground. I am not aware
that Vaschy and Heaviside had a clear knowledge of it. If I am correct,
then it is quite remarkable that Serb peasants should have been
cognizant of a physical principle which was probably unknown to English
and French savants, like Vaschy and Heaviside.
Passing now by analogy from motion of matter to motion of electricity,
we can, speaking figuratively, state that vibratory motion of
electricity will be transmitted from one end of a conducting wire to
the other the more efficiently the heavier and the less compressible
that electricity is, or, dropping now our figurative mode of speech,
we can say that, other things being equal, the higher the kinetic and
the elastic reaction of the moving electricity the more efficiently
will the energy of its vibratory motion be transmitted over the wire.
But that means that the inductance of the wire should be made as large
and its capacity as small as possible. That much was perfectly obvious
in Thomson’s and Kirchhoff’s work, some twenty years before Vaschy and
Heaviside took up the mathematical theory of telephonic transmission.
These two celebrated mathematicians, however, deserve much credit for
their enthusiastic backing of inductance among the sceptical telephone
engineers, who, at that time, knew little of the mathematical theory
and of the general principle of transmission of vibratory motions.
A coil of wire wound around an iron core is the first picture in our
mind when we hear inductance mentioned. Hence, if inductance increases
the efficiency of transmission in a telephone transmission-line, and
you cannot introduce it into the line in large amounts in any other
way, then one would certainly suggest putting a lot of coils into the
telephone-line and examining the results of this haphazard guess.
Vaschy tried this guess, and failed. The late Mr. Pickernell, chief
engineer of the long-distance department of the American Telephone and
Telegraph Company, also tried it, and he also failed. It was obvious
that, as Heaviside expressed it, experiment gave no encouragement with
regard to inductance introduced in this way. I tried it and found that
experiment offered very much encouragement to inductance introduced
this way; I succeeded, because I did not guess; I was guided by the
mathematical solution of the generalized La Grangian problem. What
does this solution say when applied to electrical motions in a wire?
It says this: Place your inductance coils into your telephone-line at
such distances apart that for all vibratory motions of electricity
which it is desirable to transmit there shall be several coils per
wave-length. In telephonic transmission of speech that means one coil
every four or five miles on overhead wires, and one coil in about every
one to two miles in a telephone cable. For these wave-lengths, the wire
possessing discreet lumps of inductance in the form of inductance-coils
acts like a wire with uniformly distributed inductance. Such a wire
transmits efficiently according to the general physical principle
described above. In order to illustrate this by a mechanical analogy,
we can say that a light silk cord stretched between two fixed points
and carrying at equidistant points heavy bird-shot will act like a
heavy uniform cord for all vibratory motions the wave-length of which
embraces several intervals separating the bird-shot, and will transmit
these motions much more efficiently from one end of the cord to the
other than if the bird-shot were not there. This simple experiment
with bird-shot and a long stretched cord can easily be tried; it is
a very inexpensive experiment and will convince you even if you know
nothing about the mathematical elements of the problem. This is the
simple experiment which I had in my head during my tramping along the
zigzag roads in Switzerland in 1894. A professor of physics, who often
acted as consulting physicist to telephone companies, had such a loaded
cord hung up over his lecture-room table for the purpose of explaining
transmission of wave-motion from one end of the cord to the other, but
he never inferred anything from it regarding loading a telephone-line
with inductance-coils. When I called his attention to it, and joked
about it, he blamed his hard luck, implying, I thought, that solving a
dynamical problem and building upon the foundation of this solution an
electrical invention is a question of luck.
From the simple apparatus, just referred to, to the elaborate
electrical demonstrations which would convince stubborn and
hard-headed telephone engineers, was a very long pull. The most
embarrassing feature in these demonstrations was that I could not
afford large expenditures of money to carry them out on actual
telephone conductors; besides, it would have been unwise to disclose
to interested parties, the owners of long-distance telephone-lines, a
theory for which I had not yet obtained a satisfactory experimental
proof. I had to invent laboratory apparatus equivalent to telephone
lines or cables of great length, which would enable me to do all the
experimenting in my laboratory. That required almost as much thought,
inventive effort, and mathematical achievement as the solution of the
extended La Grangian problem.
The first part of my research I communicated to the American Institute
of Electrical Engineers in March, 1899. It dealt only with the
mathematical theory of my laboratory apparatus. It spoke a great deal
about La Grange, but nothing directly about the invention. In October
of that year, a friend of mine, Doctor Cary T. Hutchinson, told me
that he suspected that an invention was hidden in that communication.
“If you have detected it, others have detected it also, and are by
this time in the Patent Office,” said I. “Are you not there yourself?”
asked Hutchinson, looking somewhat disturbed, and when he heard that I
was not he looked discouraged. When, however, I declared my readiness
to undertake to design for some clients of his a telephone cable to
operate between New York and Boston, guaranteeing to employ a wire not
bigger than in ordinary cables capable of operating satisfactorily
over a distance of only twenty miles, Hutchinson grew quite serious,
and advised me to apply for a patent before doing anything else. I
finally followed his advice, and not any too soon. There were others,
besides Hutchinson, who had recognized that in my communication to
the American Institute of Electrical Engineers there was hidden an
invention for which telephone engineers had been eagerly waiting ever
since the birth of the telephone art. This created an interference in
the Patent Office which annoyed me, but not nearly so much as I had
been annoyed there before. About a year from the date of my application
for patent, the American Telephone and Telegraph Company acquired my
American patent rights, treating me most generously. It gave me what I
asked; my friends thought that I had not asked enough, but to a native
of Idvor a dollar looks much bigger than to a native of New York who
may be a next-door neighbor to some Morgan or Rockefeller. Besides,
the opinion of the highest telephone authority in the world that my
solution of the extended La Grangian problem had a very important
technical value was much more gratifying to me than all the money in
the world.
In Europe, and particularly in England, the invention came as a
surprise; they did not expect an American to make an invention which
required so much mathematical analysis of electrical motions, to which
the American physicist had contributed very little, whereas Vaschy and
Heaviside had written volumes about it. But these writers had paid too
little attention to classical writers like La Grange, Thomson, and
Kirchhoff. The construction of the inductance-coil required almost as
much mathematical analysis as the dynamical theory of the invention,
and the method of testing it also was new to the telephone engineers.
The coil is now known all over the world as the Pupin coil, and many
people think that the coil itself is the invention.
When it became known that I had studied at the Universities of
Cambridge and of Berlin, my English and German friends claimed the
credit of the invention for the scientific training which I had
received at their universities. I think the French had a better
claim, because it was La Grange who helped me more than any other
mathematical reading. As a matter of fact, the engineers of the
American Telephone and Telegraph Company and the herdsmen of Idvor
deserve most of the credit. The first formulated the problem the
solution of which led to the invention, and the second taught me the
art of signalling through the ground which guided me to the physical
principle which underlies the invention.
A vice-president of the American Telephone and Telegraph Company, who
is a very high authority in telephony, informed me recently that one
way to describe, roughly, the value of the invention is as follows:
If during the past twenty-two years his company had been compelled to
extend its network of conductors so as to give, without employing my
invention, the same service which it is giving to-day, it would have
had to spend at least one hundred million dollars more than it has
actually expended. But after quoting him I wish to call attention to
a fact which the public often overlooks. I ask, where are those one
hundred million dollars which the invention has saved? I know that not
even a microscopic part of them is in the pockets of the inventor.
I have figured out also, with the same accuracy with which I once
figured out the invention, that those hundred million dollars are not
in the pockets of the telephone company. They must be, therefore, in
the pockets of the American public. The invention made it possible to
give the telephone service, which is now being given, at a lower rate
than would have been possible if one hundred million dollars more had
been spent. Every good invention benefits the public immeasurably more
than it benefits the inventor or the corporation which exploits the
invention. I certainly consider myself a public benefactor, and the
National Institute of Social Sciences called me so when it gave me a
gold medal almost as big as the full moon. But this gift would have
made me much more happy if the institute had at the same time given
another gold medal to the American Telephone and Telegraph Company.