LAWS ON THE GENERATION OF ELECTRICITY BY PRESSURE, IN TOURMALINE. Pgs. 15-17
LOIS
DEGAGEIENT DE L’ELECTRICITE PAR PRESSION,
DANS LA TOURMALINE.
En commun avec JACQUES CURIE.
Comptes rendus de I’Academie des Sciences , t. X.C1I, p. 1B6,
seance du 24 janvier 1881.
LAWS
ON THE GENERATION OF ELECTRICITY BY PRESSURE,
IN TOURMALINE.
In collaboration with JACQUES CURIE.
Proceedings of the Academy of Sciences, vol. XCII, p. 186,
session of January 24, 1881.
Nous alions d’abord enoncer les lois qui resultent de nos expe¬ riences sur le de gage men t par pression de 1 electricite dans la tourmaline. Nous exposerons ensuite, avec la rapidite qu exige la brieve te de cette Note, nos procedes d’experiences et les limites entre lesquelles nous avons verifie ces lois.
We will first state the laws derived from our experiments on the discharge of electricity from tourmaline under pressure. We will then outline, as briefly as the brevity of this Note requires, our experimental procedures and the limits within which we have verified these laws.
I. Les deux extremites cV une tourmaline degagent des quantiles d’ electricite de signes contraires egales entre elles.
II. La quantite mise en liberte par une certaine augmenta¬ tion de pression est de signe contraire et egale d celle produite par une egale diminution de pression.
III. Cette quantite est proportionnelle a la variation de pression .
IV. Elle est independante de la longueur de la tourmaline.
V. Pour une meme variation de pression par unite de sur¬ face, elle est proportionnelle a la surface.
I. The two ends of a tourmaline emit quantities of electricity of opposite signs that are equal in magnitude.
II. The quantity released by a certain increase in pressure is of opposite sign and equal to that produced by an equal decrease in pressure.
III. This quantity is proportional to the change in pressure.
IV. It is independent of the length of the tourmaline.
V. For the same change in pressure per unit area, it is proportional to the area.
Le resultat direct des experiences d’ou Lon deduit les lois IV -et V peut s’enoncer d’une facon simple : Pour une meme vaiiation de pression la quantite d’ electricite qui se degage est independante des dimensions de la tourmaline.
The direct result of the experiments from which we derived Laws IV and V can be stated simply as follows: For a given change in pressure, the amount of electricity released is independent of the dimensions of the tourmaline.
Les lourmalines que i’on vouiait etudier avaient la forme de prismes paralleles a l’axe principal. Les deux bases etaient recouvertes de deux feuilles d’etain, protegees exterieurement par deux plaques de verre tres epaisses, entre lesquelles on comprimait le cristal a 1’aicle d’un solicle levier en bois. lAme des feuilles d’etain etant en communication avec le sol, l’autre etait reliee a 1’ aiguille d’un electrometre Thomson-Mascart. La deviation obtenue a la suite d une variation de pression etait proportionnelle a la quantite d’electricite degagee, la capacite de la feuille d’etain, dans les con¬ ditions C| u i viennent d’etre clecrites, etant toujours negligeable devant la capacite de l’electrometre.
The transparent samples to be studied were shaped like prisms parallel to the main axis. The two bases were covered with two sheets of tin, protected on the outside by two very thick glass plates, between which the crystal was compressed by the tip of a wooden lever. One of the tin sheets was in contact with the ground, while the other was connected to the needle of a Thomson-Mascart electrometer. The deflection obtained following a pressure variation was proportional to the amount of electricity released, the capacitance of the tin foil, under the conditions just described, being negligible compared to the capacitance of the electrometer.
Les tourmalines transparentes, incolores ou legerement colorees en vert, jaune ou rose, sont, en general, parfaitement isolantes, et ce sont celles-la seulement qui out servi aux experiences quantitatives. Quelle que soit leur coloration, ces tourmalines sem blent etre a pen pres equivaientes au point de vue des phenomenes electriques ; les clillerences, s’ll j en a, sont certainement tres petites; cependant il serai t necessaire de passer en revue un nombre con¬ siderable d’echantillons avant de pouvoir affirmer cju’il en est toujours ainsi.
Transparent tourmalines, whether colorless or lightly tinted green, yellow, or pink, are generally excellent insulators, and only these have been used in quantitative experiments. Regardless of their coloration, these tourmalines appear to be nearly equivalent in terms of electrical phenomena; any differences, if any, are certainly very small; however, it would be necessary to examine a considerable number of samples before being able to affirm that this is always the case.
Les tourmalines plus ou moins opaques ou noires sont conductrices de I’electricite. Une tourmaline noire donnait une impulsion de 1’ aiguille de l’electrometre egale au cinquieme environ de la deviation obtenue pour un meme poids avec une tourmaline transparente ; de plus, 1 aiguille revenait rapidement au zero.
Tourmalines that are more or less opaque or black are conductors of electricity. A black tourmaline caused the needle of the electrometer to deflect by about one-fifth of the deflection obtained for the same weight with a transparent tourmaline; furthermore, the needle quickly returned to zero.
Les deviations dont il etait necessaire de verifier l’egalite ou la proportionnalite n’etaient exactes, vu les causes cl’erreur negligees, qu a un vingtieme de leur valeur. Nous n’avons pas juge neces¬ saire cl essajer d atteindre une approximation plus grande, car l’exactitude des lois enoncees ressorl des dilferences considerables entre les dimensions des tourmalines employees.
The deviations for which it was necessary to verify equality or proportionality were accurate, given the negligible sources of error, to only one-twentieth of their value. We did not deem it necessary to attempt to achieve a greater degree of accuracy, since the validity of the stated laws is evident from the considerable differences in the dimensions of the tourmalines used.
Pour une meme surface, les longueurs ont varie depuis omm, 5 juscju’a i 5mm, done dans la proportion de i a 3o. Pour une meme longueur, les surfaces ont varie depuis 2mm2 jusqu’a icm2, done dans la proportion de i a 5o. Etant donnee l’approximation des expe¬ riences et en supposant les lois enoncees comme etant des lois limites, on pent done certifier, lorsqu’on double la longueur, que la difference avec la loi veritable est inferieure a un six-centieme, et, lorsqu’on double la surface, qu’elle est inferieure a unmillieme.
For the same area, the lengths varied from 0.5 mm to 15 mm, a ratio of 1 to 30. For the same length, the areas varied from 2 mm² to 1 cm², a ratio of 1 to 50. Given the approximation of the experiments and assuming the stated laws to be limiting laws, we can therefore certify that, when the length is doubled, the difference from the true law is less than one six-hundredth, and, when the area is doubled, it is less than one-thousandth.
Une parcelle de imm3 degage, pour une meme pression, la meme quantite d’electricite qu’un morceau volumineux de plusieurs cenli metres cubes. Enfin, Feffet produit par 1’ addition d’un des pre¬ miers kilogrammes est sensiblement le meme que celui produit par le centieme kilogramme pour une surface de icm\
A small volume of 1 mm³ generates, at the same pressure, the same amount of electricity as a large volume of several hundred cubic meters. Finally, the effect produced by adding the first kilogram is substantially the same as that produced by the hundredth kilogram for a surface area of 1 cm².
Dans un remarquable travail, Gaugain a montre la simplicity des phenomenes pyro-electriques de la tourmaline. Les lois qu’il a enoncees peuventetre placees en regard de celles qui font l’objet de cette Note. II est facile de voir qu’elles peuvent etre calquees Tune sur I 'autre, si i’on se laisse guider par bhypothese que nous avons emise, et qui consiste a admettre que les phenomenes resultant des variations de pression ou ceux resultant des variations de temperature sont dusa une seule et meme cause : la contraction ou la dilatation suivant I’axe de la tourmaline.
In a remarkable study, Gaugain demonstrated the simplicity of the pyroelectric phenomena of tourmaline. The laws he formulated can be compared with those discussed in this Note. It is easy to see that they can be superimposed one upon the other, if one is guided by the hypothesis we have put forward, which consists in admitting that the phenomena resulting from variations in pressure or those resulting from variations in temperature are due to one and the same cause: contraction or expansion along the axis of the tourmaline.
Overview In this third report to the Academy of Sciences, Pierre and Jacques Curie establish the first five mathematical laws governing the generation of electricity via pressure in Tourmaline crystals. This paper transitions the study of piezoelectricity from a curiosity of mineralogy into a rigorous branch of physics.
The Five Laws of Piezoelectricity
Symmetry of Charge: The two ends of the crystal produce exactly equal amounts of opposite electrical charges.
Reversibility: Compression and decompression produce equal and opposite charges.
Proportionality: The amount of electricity produced is directly proportional to the amount of pressure applied (a linear relationship).
Independence of Length: The length of the crystal does not affect the amount of electricity generated.
Dependence on Area: For a set amount of pressure, the electricity produced is proportional to the surface area of the crystal faces.
Key Technical Findings
The "Massive" Discovery: The Curies noted a startling fact: for a given pressure, a tiny crystal produces the same amount of electricity as a hypothetical crystal measuring several hundred cubic meters. This proved that piezoelectricity is a property of the crystal's structure and surface area, not its total volume.
Insulation vs. Conductivity: They determined that only transparent (clear) tourmalines work for these experiments because they are excellent insulators. Black or opaque tourmalines are too conductive, allowing the electricity to "leak" away before it can be measured.
Instrumentation: To achieve their precision (accurate to within 1/20th of the values), they utilized a Thomson-Mascart electrometer, demonstrating their prowess in experimental design.
Conclusion The Curies conclude that these laws mirror the laws of heat-based electricity (pyroelectricity) discovered by Gaugain, confirming their theory that both phenomena are caused by the same physical change: the expansion or contraction of the crystal's atomic lattice.
