ON PIEZOELECTRIC PHENOMENA.
SUR
LES PHENOMENES PIEZO ELECTRI QUES.
Bulletin des seances de la Societe francaise cle Physique,
an nee 1887, P- 47-
ON
PIEZOELECTRIC PHENOMENA.
Proceedings of the French Physical Society,
Year 1887, p. 47-
M. P. Curie pense que la conductibilite, dans la theorie de M. Duhem, est une conductibilite fictive qui intervient coniine un artifice de calcul. Prenons une tourmaline avec circuit exterieur conducteur reunissant ses extremites ; en faisant varier la temperature du cristal, les phenomenes electriques sont absolmuent dilferents de cem que Ton obtient en faisant naitre et disparaitre une force electromotrice dans le circuit exterieur.
Mr. P. Curie believes that conductivity, in Mr. Duhem’s theory, is a fictitious conductivity that serves merely as a computational device. Consider a tourmaline with an external conductive circuit connecting its ends; by varying the temperature of the crystal, the electrical phenomena are completely different from those obtained by inducing and removing an electromotive force in the external circuit.
M. Curie admetque les phenomenes pjro- et piezo-electriques ont une origine commune, la deformation du cristal. Mais il ne saurait admettre qu’ils soient identiques et que la compression n'agisse que comme producteur de chaleur. Les elFets calorifiques mis en jeu par la compression sont beaucoup trop minimes pour expliquer le degagement d’electricite observe. De plus, le dcgagement d’electrieite par pression est instantane, ce qui ne serai t pas s’il fa 11 ait attendre le refroidissement du cristal.
Mr. Curie acknowledges that the pyroelectric and piezoelectric phenomena have a common origin: the deformation of the crystal. But he cannot accept that they are identical, nor that compression acts solely as a source of heat. The heat effects involved in compression are far too small to explain the observed generation of electricity. Furthermore, the generation of electricity by pressure is instantaneous, which would not be the case if one had to wait for the crystal to cool.
M. D u h em repond que I on salt, depuis M. Du Bois-Rejmond et Gaugain, que les phenomenes produits dans le circuit exterieur d une tourmaline sont identiques aux phenomenes produits dans le circuit exterieur d’une pile de grande force electromotrice et de grande resistance. Quant aux autres faits signales par M. Curie, i Is sont des consequences de la theorie de M. Duhem.
Mr. Duhem replies that, following Mr. Du Bois-Rejmond [Emil du Bois-Reymond]and Gaugain, the phenomena produced in the external circuit of a tourmaline are identical to those produced in the external circuit of a battery with high electromotive force and high resistance. As for the other facts reported by Mr. Curie, they are consequences of Mr. Duhem’s theory.
M. Vaschy fait observer qu’il sembie resulter des lois expertmen tales connues que l’electrisation Q prise par un cristal est proporlionnelle a son elevation de temper at in e (T’1-T’0) et se maintient ( sauf deperdition lente par conductibilite) lorsque la temperature finale T'1 devient uniforme dans le cristal. D apres M. Duhem, cette electrisation serait an contraire proportionnelle a la difference actuelle (T1 — T0) de temperature entre les faces et le milieu du cristal ; le maintien prolonge de la charge 0 conduirait alors a admettre que la difference (T1 — T0) se maintient en realite, alors qu’il semble que la temperature est devenue uniform e.
Mr. Vaschy observes that it appears to follow from known experimental laws that the electrification Q acquired by a crystal is proportional to its temperature rise (T’1 – T’0) and is maintained (except for slow loss due to conductivity) when the final temperature T’1 becomes uniform throughout the crystal. According to Mr. Duhem, this electrification would, on the contrary, be proportional to the current temperature difference (T1 — T0) between the faces and the center of the crystal; the prolonged maintenance of the charge would then lead one to conclude that the difference (T1 — T0) is in fact maintained, even though it appears that the temperature has become uniform.
M. Duhem repond que la charge Q ne se maintient, apres que la temperature est devenue unilorme, que dans les ciistaux mauvais conducteurs; il n’a envisage que les substances e o nd uc trices.
Mr. Duhem replies that, once the temperature has become uniform, the charge Q persists only in poor conductors; he has considered only conductive substances.
Historical Summary and Context
This brief transcript from the Proceedings of the French Physical Society (1887) records a public scientific debate between Pierre Curie and the thermodynamicist Pierre Duhem, with contributions from Anatole Vaschy. It takes place five years after the last paper in the series and reveals that, despite the Curies' experimental work, the theoretical interpretation of piezoelectricity remained actively contested in the French scientific community.
1. Who Are the Participants?
Pierre Curie needs no introduction in this series. By 1887 he was the established experimental authority on piezoelectricity.
Pierre Duhem (1861-1916) was one of the most important French theoretical physicists and philosophers of science of the era. He is best known today for the Duhem-Quine thesis in philosophy of science. In 1887 he was developing a thermodynamic theory of electromagnetism that attempted to unify pyroelectricity and piezoelectricity under a single thermodynamic framework. He would later become famous for his historical work on medieval science.
Anatole Vaschy (1857-1899) was a French engineer and physicist best known for independently developing what is now called the Buckingham Pi theorem — a foundational result in dimensional analysis. His intervention here is characteristically mathematical and precise.
Emil du Bois-Reymond (1818-1896), cited by Duhem, was a German physiologist who pioneered the study of bioelectricity and established the analogy between biological electrical phenomena and battery circuits — the same analogy Duhem applies to tourmaline.
2. What Is the Debate About?
The core disagreement is about the physical mechanism behind piezoelectricity and pyroelectricity. There are three positions in conflict:
Duhem's Position — Thermodynamic Unification Duhem argues that pyroelectricity and piezoelectricity are the same phenomenon at root. In his framework:
Compression generates heat (which is true — this is the well-known thermodynamic effect of adiabatic compression).
That heat creates a temperature gradient within the crystal.
The temperature gradient drives the electrical polarisation.
Therefore pressure and temperature are just two different ways of achieving the same thermal effect.
He models the crystal as a high-resistance, high-EMF battery — the same analogy used by Gaugain and du Bois-Reymond.
Curie's Position — Direct Mechanical Effect Pierre Curie flatly rejects this. His experimental evidence is decisive on two points:
The heat generated by compression is far too small to account for the observed electrical output. The numbers simply do not add up thermally.
The effect is instantaneous. If the electricity were caused by heat flowing through the crystal, there would be a measurable time delay. There is none. Pressure produces electricity immediately, which proves it is a direct mechanical-electrical coupling, not a thermal intermediate.
Vaschy's Contribution — A Mathematical Test Vaschy makes a precise and elegant observation. He notes that experimental evidence shows:
Charge Q is proportional to the total temperature change (T'_1 - T'_0) and persists after the temperature becomes uniform throughout the crystal.
This directly contradicts Duhem's theory, which predicts:
Charge Q should be proportional to the instantaneous temperature difference between the faces and the centre (T_1 - T_0)$.
Once temperature becomes uniform, the charge should disappear (since the gradient driving it has vanished).
Vaschy is essentially pointing out that Duhem's theory makes a testable prediction that is experimentally falsified. Duhem retreats slightly, arguing that his theory only applies to conductive substances, and that in poor conductors the charge persists for different reasons. This is a significant qualification that effectively limits the scope of his theory considerably.
3. Who Was Right?
Curie was correct. Modern physics fully vindicates his position:
Piezoelectricity is a direct electromechanical coupling arising from the displacement of ions in an asymmetric crystal lattice under mechanical stress.
It has nothing to do with heat generation from compression — the thermal effects are real but entirely negligible in magnitude.
The effect is indeed instantaneous at the macroscopic scale.
Pyroelectricity and piezoelectricity, while related by crystal symmetry requirements, are distinct physical phenomena with different microscopic mechanisms.
Duhem's thermodynamic approach, while mathematically elegant, was attempting to force a unified framework onto two phenomena that are related but not identical. His model was essentially a sophisticated version of Gaugain's discredited theory from 1856 — the same theory Pierre Curie had experimentally demolished in the February 1881 paper.
4. Why This Document Matters
This transcript is historically significant for several reasons:
It shows that experimental discovery does not immediately end theoretical debate — even with overwhelming experimental evidence, competing theoretical frameworks persisted for years.
It captures Pierre Curie in a rare public argumentative role — most of his papers are measured and careful. Here we see him being direct and dismissive of a theory he considers physically untenable.
It marks the last appearance of the Gaugain-battery analogy as a serious scientific position — after this debate, the direct mechanical interpretation of piezoelectricity became the consensus.
It foreshadows Pierre Curie's later theoretical work on crystal symmetry (1894), in which he developed the systematic group-theoretic framework that finally provided the rigorous theoretical foundation his experimental discoveries had been waiting for.
