DREAMS OF YOUTH. FIRST SCIENTIFIC WORK.
DISCOVERY OF PIEZO-ELECTRICITY
Pierre Curie was still very young when he began his higher studies in
preparation for the licentiate in physics. He followed the lectures and
laboratory work at the Sorbonne and had, besides, access to the
laboratory of Professor Leroux in the School of Pharmacy, where he
assisted in the preparation of the physics courses. At the same time he
became further acquainted with laboratory methods by working with his
brother Jacques, who was then preparator of chemistry courses under
Riche and Jungfleisch.
Pierre received his licentiate in physical sciences at the age of
eighteen. During his studies he had attracted the attention of Desains,
director of the University laboratory, and of Mouton, assistant director
of the same laboratory. Thanks to their appreciation he was appointed,
when only nineteen years old, preparator for Desains and placed in
charge of the students' laboratory work in physics. He held this
position five years, and it was during this time that he began his
experimental research.
It is to be regretted that because of his financial situation Pierre was
obliged, at this early age of nineteen, to accept the post of preparator
instead of being able to give his whole time for two or three years
longer to his University studies. With his time thus absorbed by his
professional duties and his investigations he had to give up following
the lectures in higher mathematics, and he therefore passed no further
examinations. In compensation, however, he was released from military
service in conformity with the privileges at that time accorded young
men who undertook to serve as teachers in the public-school system.
He was by this time a tall and slender young man with chestnut-colored
hair and a shy and reserved expression. At the same time his youthful
face mirrored a profound inner life. One has such an impression of him
as he appears in a good group photograph of Doctor Curie's family. His
head is resting on his hand in a pose of abstraction and reverie, and
one cannot but be struck by the expression of the large, limpid eyes
that seem to be following some inner vision. Beside him the brown-haired
brother offers a striking contrast, his vivacious eyes and whole
appearance suggesting decision.
The two brothers loved each other tenderly and lived as good comrades,
being accustomed to work together in the laboratory and walk together in
their free hours. They also kept up affectionate relations with a few of
their childhood friends: Louis Depouilly, their cousin, who became a
physician; Louis Vauthier, also later a physician; and Albert Bazille,
who became an engineer in the post and telegraph service.
Pierre used to tell me of the vivid memories he had of the vacations
passed at Draveil on the Seine, where, with his brother Jacques, he took
long walks beside the river, agreeably interrupted by swimming and
diving in the stream. Both brothers were excellent swimmers. Sometimes
they tramped for entire days. They had, at an early age, acquired the
habit of visiting the suburbs of Paris on foot. At times also Pierre
made solitary excursions which well suited his meditative spirit. On
these occasions he lost all sense of time, and went to the extreme limit
of his physical forces. Absorbed in delightful contemplation of the
things about him, he was not conscious of material difficulties.
On the pages of a diary written in 1879,[1] he thus expressed the
salutary influence of the country upon him:
"Oh, what a good time I have passed there in that gracious solitude, so
far from the thousand little worrying things that torment me in Paris.
No, I do not regret my nights passed in the woods, and my solitary days.
If I had the time I would let myself recount all my musings. I would
also describe my delicious valley, filled with the perfume of aromatic
plants, the beautiful mass of foliage, so fresh and so humid, that hung
over the Bièvre, the fairy palace with its colonnades of hops, the
stony hills, red with heather, where it was so good to be. Oh, I shall
remember always with gratitude the forest of the Minière; of all the
woods I have seen, it is this one that I have loved most and where I
have been happiest. Often in the evening I would start out and ascend
again this valley, and I would return with twenty ideas in my head."
Thus, for Pierre Curie, the sensation of well-being he experienced in
the country was derived from the opportunity for tranquil reflection.
Daily life in Paris with its numerous interruptions did not permit of
undisturbed concentration, and this was to him a cause of inquietude and
suffering. He felt himself destined for scientific research; for him the
necessity was imperative of comprehending the phenomena of Nature in
order to form a satisfactory theory to explain them. But when trying to
fix his mind on some problem he had frequently to turn aside because of
the multiplicity of futile things that disturbed his reflections and
plunged him into discouragement.
Under the heading, "A day like too many others," he enumerated in his
diary a list of the puerile happenings that had completely filled one of
his days, leaving no time for useful work. He then concluded: "There is
my day, and I have accomplished nothing. Why?" Further on he returns to
the same theme under a title borrowed from Victor Hugo's "Le Roi
S'Amuse,"
"To deafen with little bells the spirit that would think."
"In order that, weak one that I am, I shall not let my head turn with
all the winds, yielding to the least breath that touches it, it is
necessary that all should be immobile about me, or that, like a spinning
top, movement alone should render me insensible to external objects.
"When, in the process of turning slowly upon myself, I try to gain
momentum, a nothing, a word, a story, a paper, a visit stops me and is
able to put off or retard forever the moment when, granted a sufficient
swiftness I might have, in spite of my surroundings, concentrated on my
own intention.... We must eat, drink, sleep, be idle, love, touch the
sweetest things of life and yet not succumb to them. It is necessary
that, in doing all this, the higher thoughts to which one is dedicated
remain dominant and continue their unmoved course in our poor heads. It
is necessary to make a dream of life, and to make of a dream a reality."
This acute analysis, sufficiently surprising in a young man of twenty
years, suggests in an admirable manner the conditions necessary to the
highest manifestations of the intellect. It carries a lesson which, if
it were sufficiently understood, would facilitate the way of all
contemplative spirits capable of opening new paths for humanity.
The unity of thought toward which Pierre Curie strove was troubled not
only by professional and social obligations but also by his tastes,
which urged him towards a broad literary and artistic culture. Like his
father, he loved reading, and did not fear to undertake arduous literary
tasks. To some criticism made in this connection, he responded readily:
"I do not dislike tedious books." This meant that he was fascinated by
the search after truth which is sometimes associated with writing devoid
of charm. He also loved painting and music, and went gladly to look at
pictures or to attend a concert. A few fragments of poetry in his
handwriting were left among his papers.
But all these preoccupations were subordinated in his mind to what he
considered his true task, and when his scientific imagination was not in
full activity, he felt himself, in a sense, an incomplete being. He
expressed this inquietude with an emotion born of his suffering during
momentary periods of depression.
"What shall I become?" he wrote. "Very rarely have I command of all
myself; ordinarily a part of me sleeps. My poor spirit, are you then so
weak that you cannot control my body? Oh, my thoughts, you count indeed
for very little! I should have the greatest confidence in the power of
my imagination to pull me out of the rut, but I greatly fear that my
imagination is dead."
But despite hesitations, doubts, and lost moments, the young man was
little by little striking out his path and strengthening his will. He
was resolutely carrying on fruitful investigations at an age when many
men who were to become savants were as yet only pupils.
His first work, done in collaboration with Desains, concerned the
determination of the lengths of heat waves with the aid of a
thermoelectric element and a metallic wire grating, a process, then
entirely new, which has since often been employed in the study of this
question.
Following this he undertook an investigation on crystals in
collaboration with his brother, who had passed his licentiate and was
preparator for Friedel in the laboratory of mineralogy at the Sorbonne.
Their experiments led the two young physicists to a great success: the
discovery of the hitherto unknown phenomena of piezo-electricity, which
consists of an electric polarization produced by the compression or the
expansion of crystals in the direction of the axis of symmetry. This was
by no means a chance discovery. It was the result of much reflection on
the symmetry of crystalline matter, which enabled the brothers to
foresee the possibilities of such polarization. The first part of the
investigation was made in Friedel's laboratory. With an experimental
skill rare at their age, the young men succeeded in making a complete
study of the new phenomenon, established the conditions of symmetry
necessary to its production in crystals, and stated its remarkably
simple quantitative laws, as well as its absolute magnitude for certain
crystals. Several well-known scientists of other nations (Roentgen,
Kundt, Voigt, Riecke) have made further investigations along this new
road opened by Jacques and Pierre Curie.
The second part of the work, and much more difficult to realize
experimentally, concerned the compression resulting in piezo-electric
crystals when they are exposed to the action of an electric field. This
phenomenon, foreseen by Lippmann, was demonstrated by the Curie
brothers. The difficulty of the experiment lay in the minuteness of the
deformations that had to be observed. Fortunately Desains and Mouton
placed a small room adjoining the physics laboratory at the disposal of
the brothers so that they might proceed successfully with their delicate
operations.
From these researches, as much theoretical as experimental, they
immediately deduced a practical application, in the form of a new
apparatus, a piezo-electric quartz electrometer, which measures in
absolute terms small quantities of electricity, as well as electric
currents of low intensity. This apparatus has since then rendered great
service in experiments in radioactivity.[2]
During the course of their experiments on piezo-electricity the Curies
were obliged to employ electrometric apparatus, and, not being able to
use the quadrant electrometer known at that time, they developed a new
form of that instrument, better adapted to their necessities. This
became known in France as the Curie electrometer. Thus these years of
collaboration between the two brothers, always intimately united, proved
both happy and fruitful. Their devotion and their common interest in
science were to them both a stimulant and a support. During their work
the vivacity and energy of Jacques were of precious aid to Pierre,
always more easily absorbed by his thoughts.
However, this beautiful and close collaboration lasted only a few years.
In 1883, Pierre and Jacques were obliged to separate; Jacques left for
the University of Montpellier as Head Lecturer in Mineralogy (_Maître de
Conferences_). Pierre was made Director of Laboratory Work in the School
of Industrial Physics and Chemistry founded by the city of Paris at the
suggestion of Friedel and of Schützenberger, who became its first
director. Their remarkable researches with crystals won for the brothers
in 1895--very late, it is true--the Planté prize.
[Footnote 1: Pierre Curie did not leave a veritable diary but only a few
pages as chance permitted, covering but a short period of his life.]
[Footnote 2: The piezo-electric property of quartz has recently had an
important application; it has been utilized by P. Langevin in the
production of elastic waves of high frequency (beyond sound) sent out in
water with the aim of detecting submarine obstacles. This same method
can serve in a more general manner to explore ocean depths. We see,
here, once again, how pure speculation can lead to discoveries that will
be useful later in unforeseen directions.]