THE HEMIHEDRAL CRYSTALS WITH INCLINED FACES, AS CONSTANT SOURCES OF ELECTRICITY. Pgs. 22-25
LES
CRISTAUX HEMIEDRES A FACES INCLINEES,
COMME SOURCES CONSTANTES D’ELECTRICITE.
En commun avec JACQUES CURIE.
Comptes rendus de V Academie des Sciences, t. XCIII, p. 204,
seance du 25 juillet 1881.
THE
HEMIHEDRAL CRYSTALS WITH INCLINED FACES,
AS CONSTANT SOURCES OF ELECTRICITY.
In collaboration with JACQUES CURIE.
Proceedings of the French Academy of Sciences, vol. XCIII, p. 204,
session of July 25, 1881.
I. Une lame convenablement taillee clans un cristal hemiedre a faces inclinees et placee entre deux feuilles d’etain eonstilue un condensateur qui est susceptible de se charger lui-meme quand on le comprime. On peut realiser avec ce systeme un instrument nouveau, une sorte de condensateur-source qui jouit de proprietes speciales. Nous allons indiquer ces proprietes, qui resultent des lois que nous avons etablies prececlemment pourle degagement de I’electricite dans les cristaux bemiedres ; nous montrerons comment cet instrument peut servir, comme etalon d’electricite static|ue, a la mesure des charges et a celle des capacites.
Nous donnerons aussi dans cette Note une mesure absolue des quantites d'electrici te degagees par la tourmaline et le quartz pour une pression determinee.
I. A blade properly cut from a hemihedral crystal with inclined faces and placed between two sheets of tin forms a capacitor capable of charging itself when compressed. This system can be used to create a new instrument, a sort of capacitor-source that possesses special properties. We will describe these properties, which result from the laws we have previously established regarding the release of electricity in hemihedral crystals; we will show how this instrument can serve, as a standard of static electricity, for measuring charges and capacitances.
In this Note, we will also provide an absolute measurement of the quantities of electricity released by tourmaline and quartz under a given pressure.
II. II est necessaire de rappeler trois des proprietes fondamentales que possecle un cristal agissant comme condensateur-source : 1° les deux faces se chargent de quantites d’electricite rigoureusement egales et de signes contraires; 2° lorsqu une des faces est en communication avec la terre, l’autre fournit une quantite determinee d’electricite pour une pression determinee; 3° il j a proportionnalite entre la quantite d’electricite degagee et la pression exercee ( 1 ).
( 1 ) Fratiquement, la limite au dela de laquelle cette loi doit ne plus se verifier n’est jamais atteinte et la proportionna lite se maintientau deyre d’approximation des experiences, jusqu’a des pressions voisines de celles qui determinent la rupture du cristal.
II. It is necessary to recall three of the fundamental properties of a crystal acting as a capacitor-source:
the two faces become charged with exactly equal amounts of electric charge of opposite signs;
when one of the faces is connected to ground, the other supplies a specific amount of electric charge for a specific voltage;
there is a proportional relationship between the amount of electricity released and the pressure exerted (1).
(1) In practice, the limit beyond which this law ceases to hold is never reached, and the proportional relationship remains valid within the margin of error of the experiments, up to pressures close to those that cause the crystal to break.
11 resulte de ces propositions que, tandis qu’une pile permet de porter un conducteur a un potentiel determine, un condensateursource permet de fournir a un conducteur une quantitedetermin.ee d’electricite; de plus cette quantite peut etre choisie d’avance au-dessous d’une certaine grandeur.
It follows from these propositions that, while a battery allows a conductor to be brought to a specific potential, a capacitor allows a specific amount of electric charge to be supplied to a conductor; furthermore, this amount can be chosen in advance to be less than a certain value.
111. La quantite d’electricite degagee par un poids de 1 kg place sur une tourmaline est susceptible de porter une sphere de 14.2 cm au potentiel d’un daniell, c’est-a-dire qu’elle est egale a 0.0531 unite C.G.S. electrostatique.
La quantite d’electricite degagee par un poids de 1 kg sur une lame de quartz perpendiculaire a un axe horizontal est capable de porter une sphere de 16.6 cm au potentiel d’un daniell, c’est-a-dire qu’elle est egale a 0.062 unite C.G.S. electrostatique.
Ges nombres mesurent ce qu’on peut appeler les pouvoirs electriques de pression de la tourmaline et du quartz.
111. The amount of electricity released by a 1-kg weight placed on a tourmaline is sufficient to raise a 14.2-cm sphere to the potential of one daniell; that is, it is equal to 0.0531 C.G.S. electrostatic units.
The amount of electricity released by a 1-kg weight placed on a quartz plate perpendicular to a horizontal axis is capable of raising a 16.6-cm sphere to the potential of one daniell, that is, it is equal to 0.062 C.G.S. electrostatic units.
These numbers measure what might be called the electrical pressure powers of tourmaline and quartz.
IV. Les mesures absolues, clont nous venons de donner les resultats, ont ete faites a l’aide d’une potence qui appliquait la pression directement sur le cristal; mais, quand on veut employer le cristal comme source d’electricite, il est plus commode d’exercer la pression a l’aide d’un levier, et il est indispensable de le maintenir en meme temps dans une enceinte seche. 11 vaut mieux alors ne pas s’occuper des bras de levier et determiner directement, une fois pour toutes, la quantite d’electricite qui se degage pour un poids de ikg place a l’extremite du levier; si le cristal n’est jamais derange, il pourra servir d’e talon.
IV. The absolute measurements, for which we have just given the results, were made using a clamp that applied pressure directly to the crystal; however, when the crystal is to be used as a source of electricity, it is more convenient to apply pressure using a lever, and it is essential to keep it in a dry chamber at the same time. It is therefore better not to concern oneself with the lever arms and to determine directly, once and for all, the amount of electricity released for a weight of 1 kg placed at the end of the lever; if the crystal is never disturbed, it can serve as a standard.
Voici, dans tous les cas, comment on peut evaluer la cjuantite d’electricite qui se degage : 1’ aiguille d’un electrometre ThomsonMascart etant chargee a l aide d’une pile, on unit une des lames d etain du cristal a la terre, l’autre Jame a l’un des couples de secteurs de Felectrometre et en meme temps a um conducteur de capacite connue (sphere, eondensatear a lame d air, microfarad). Get ensemble de conducteurs etant isole, on met Fautre couple de secteurs de Felectrometre en communication avec Fun des poles d’un element Daniell (Fautre pole etant ala terre). L’aiguille de Felectrometre devie, et Fon ajoute des poids agissant sur le cristal jusqu’a ce que Fon ait ramene Faiguille an zero (cette operation se fait comme une pesee ordinaire, en placant et en retirant des poids, la quantite d electricite degagee ne dependant que de la pression finale). La lame du condensateur-source, Fetalon de capacite et les secteurs de Felectrometre sont alors au potentiel d un daniell, et Fon connait le poids cpii a ete necessaire pour arriver a ce resultat. On repete la meme operation apres avoir supprime Fetalon de capacite. La difference des poids obtenus dans le premier et le deuxieme eas represente le poids necessaire pour porter Fetalon de capacite au potentiel d un daniell.
Here is how, in any case, one can estimate the amount of electricity released: With the needle of a Thomson-Mascart electrometer charged by a battery, connect one of the tin blades of the crystal to ground, and the other to one of the electrometer’s sector pairs, while simultaneously connecting it to a conductor of known capacitance (sphere, air-gap capacitor, microfarad). With this set of conductors isolated, the other pair of sectors of the electrometer is connected to one of the poles of a Daniell cell (the other pole being grounded). The electrometer needle deflects, and we add weights acting on the crystal until we have brought the needle back to zero (this operation is performed like ordinary weighing, by placing and removing weights, the amount of electricity released depending only on the final pressure). The plate of the source capacitor, the capacitance element, and the electrometer sectors are then at the potential of a Daniell cell, and one knows the weight required to achieve this result. The same operation is repeated after removing the capacitance of the reference standard. The difference between the weights obtained in the first and second cases represents the weight required to bring the capacitance of the reference standard to the potential of one Daniell cell.
V. La methode que nous venons de decrire renferme en elle un procecle de comparaison des capacites. On j^eut, en elTet, deter¬ miner a Faide de trois pesees les quantites d electricite necessaires pour porter deux eonducteurs au meme potentiel, d’oii Fon tire le rapport de leurs capacites.
Au contraire, en chargeant les deux secteurs avec deux elements differents, et en cherehant les poids necessaires pour amener une meme capacite aux potentiels de cliacun d eux, on a le rapport des forces electromotrices des deux elements.
V. The method we have just described involves a process of comparing capacitances. In essence, we wish to determine, by means of three measurements, the quantities of electricity required to bring two conductors to the same potential, from which we derive the ratio of their capacitances.
Conversely, by charging the two sectors with two different elements and determining the weights required to bring the same capacitance to the potentials of each of them, we obtain the ratio of the electromotive forces of the two elements.
Enlin on peut mesurer une charge avec une grande precision : le corps charge etant mis en communication av ec le condensateursource et avec un electrometre quelconque, ee dernier accuse la presence de Felectricite ; on ramene au zero en mettant des poids sur le condensateur.
Ges methodes ont Favantage de ramener toujours Felectrometre au zero; il ne sert done plus que comme electroscope, et Fon peut employer une sensibilite plus grande. La determination des capa¬ cites et celle des charges se font ainsi avec precision. L’appareil peut encore servir comme reparateur de charge pour maintenir a un meme potentiel un corps qui perd constamment de Felectricite et qui doit rester isole.
In this way, a charge can be measured with great precision: when the charged body is connected to the source capacitor and to any electrometer, the latter indicates the presence of electricity; the reading is reset to zero by placing weights on the capacitor.
These methods have the advantage of always resetting the electrometer to zero; it then serves only as an electroscope, and one can use a higher sensitivity. The determination of capacitances and charges is thus carried out with precision. The apparatus can also serve as a charge replenisher to maintain at a constant potential a body that is constantly losing electricity and must remain isolated.
VI. Les constantes d un condensateur-source sont : i° la quantity d’eiectricite degagee par un poids de 1 kg a I’extremite du levier ; 2° sa capacite. Pour charger les corps de tres petite capacite, il y a avantage a avoir un condensateur-source de tres faible capacite; une tourmaline on un quartz de 0.01 m de hauteur et de quelques millimetres carres de surface peuvent ne pas attemdre la capacite d’une sphere de 0.01 m de rayon et fournir cles quantites d’eiectricite capables de charger au potentiel d un daniell une sphere de 3m de rayon. Pour charger cles corps d une capacite un pen plus forte, il n’y a plus grand inconvenient a augmenter la capacite du condensateur-source, et Pon peut obtenir en le faisant des quantites d’eiectricite beaucoup plus considerables; nous avons fait construire une pile de neuf lames de quartz, taillees parallelement entre elles et perpendiculairement a un axe horizontal dans un meme canon de quartz bien homogene. Chaque lame a environ 20 cm2 surface; elles sont placees les unes sur les autres en pile, separees toutefois par des fe miles d’etain; toutes les lames de rang pair ayant ete retournees, il resulte de cette disposition que, lors d’une variation cle pression exercee sur la pile, toutes les feuilles d’etain de rang pair se chargent d une electricite, toutes cedes de rang impair se chargent cle l’autre. En reunissant tons les elements en surface, c’est-a-dire en reunissant d’une part toutes les feuilles d’etain de rang pair et d’ autre part toutes cedes de rang impair, on a un condensateur-source dont la capacite est cede d’une sphere de 3.5 m de rayon. 11 fournit faci lenient de quoi charger 1/10 de microfarad au potentiel cl’un daniell, mais la difficulte qu’il y a a exercer des pressions fortes empeche seule de depasser beaucoup cette valeur; d’apres des experiences faites avec des lames de dimensions plus petites, la pile de quartz pourrait supporter sans inconvenient, vu sa grande surface, une pression cle 6000 kg et donnerait alors une quail Lite d electricite capable de charger io microfarads au potentiel d un daniell.
VI. The constants of a source capacitor are:
1) the amount of electricity released by a 1-kg weight at the end of the lever;
2) its capacitance.
To charge objects with very low capacitance, it is advantageous to use a source capacitor with very low capacitance; a tourmaline or a quartz crystal 0.01 m high and with a surface area of a few square millimeters may not reach the capacitance of a sphere with a radius of 0.01 m and can supply quantities of electricity capable of charging a sphere with a radius of 3 m to the potential of a Daniell cell. To charge bodies with a slightly higher capacitance, there is no significant drawback to increasing the capacitance of the source capacitor, and by doing so, one can obtain much more substantial quantities of electricity; we had a stack of nine quartz plates constructed, cut parallel to one another and perpendicular to a horizontal axis within a single, highly homogeneous quartz cylinder. Each plate has a surface area of approximately 20 cm²; they are stacked one on top of the other, separated, however, by thin sheets of tin; since all the even-numbered plates have been turned over, this arrangement results in the following: when the pressure exerted on the stack varies, all the even-numbered tin plates become charged with one kind of electricity, while all the odd-numbered ones become charged with the opposite kind. By bringing all the elements together on the surface—that is, by grouping all the even-numbered tin foils on one side and all the odd-numbered ones on the other—we obtain a source capacitor whose capacitance is equivalent to that of a sphere with a radius of 3.5 m. It provides sufficient capacity to charge 1/10 of a microfarad to the potential of a Daniell cell, but the difficulty of applying high pressures alone prevents this value from being significantly exceeded; based on experiments conducted with smaller plates, the quartz stack could, given its large surface area, withstand a pressure of 6,000 kg without issue and would then provide a quantity of electricity capable of charging 10 microfarads to the potential of a Daniell cell.
Overview
Presented to the Academy of Sciences on July 25, 1881, this paper by Pierre and Jacques Curie represents the transition of piezoelectricity from a laboratory phenomenon into a practical measurement technology. They describe the design of the world's first piezoelectric instrument, a precision electrical charge source, and provide the first absolute measurements of the piezoelectric coefficients of both tourmaline and quartz.
1. The Piezoelectric Crystal as a Capacitor
The Curies begin by reframing the piezoelectric crystal not as a curiosity but as a functional electrical component. A crystal slice placed between two tin foil sheets behaves as a self-charging capacitor with three key properties:
Both faces charge to equal and opposite amounts.
When one face is grounded, the other delivers a predictable charge at a predictable voltage.
The charge delivered is proportional to the pressure applied (within practical limits up to the breaking point of the crystal).
This reframing is conceptually important: it means the crystal can be used as a reproducible, controllable source of known electrical charge — something that was very difficult to achieve with the batteries and static machines available at the time.
2. First Absolute Measurements of Piezoelectric Coefficients
The Curies provide the first quantitative measurements of what we now call the piezoelectric charge coefficient:
Tourmaline 1 kg - 14.2 cm - sphere - 1 Daniell - 0.0531 CGS
Quartz 1 kg - 16.6 cm - sphere - 1 Daniell - 0.062 CGS
Quartz produces approximately 17% more charge per kilogram than tourmaline, which is one of the early indicators that quartz would become the dominant piezoelectric material in technology.
3. A New Precision Instrument
The heart of the paper is the description of a new instrument, the world's first piezoelectric electrometer. Its operating principle is elegant:
A crystal under a lever arm delivers a known charge proportional to the weight placed on the lever.
A Thomson-Mascart electrometer detects when the system reaches the potential of a standard Daniell cell (a reference battery).
By adding or removing weights until the electrometer reads zero, the operator can measure unknown charges and capacitances with high precision.
The key advantage over existing methods is that the electrometer is always reset to zero, meaning it functions purely as a null detector rather than a measuring device. This dramatically increases precision, because null-point measurements are far less sensitive to instrument drift and calibration errors.
4. Applications Described
The Curies describe three specific applications of their instrument:
Measuring electrical capacitance — by comparing the weights needed to charge two different conductors to the same potential.
Measuring electromotive force — by comparing the weights needed to charge the same conductor to the potential of two different battery cells.
Maintaining constant potential — the device can act as a charge replenisher for a body that is slowly losing electricity, keeping it at a fixed voltage.
5. The Quartz Stack — A Prototype Piezoelectric Transducer
The final section describes what is arguably the most forward-looking invention in all four papers: a stacked quartz plate assembly consisting of nine quartz plates cut from a single homogeneous cylinder, separated by alternating tin foil sheets, with every other plate reversed so that all even plates charge one way and all odd plates charge the other.
This arrangement — which is functionally identical to the stacked piezoelectric transducers used in modern ultrasound machines, sonar systems, and industrial sensors — multiplies the charge output dramatically:
Nine plates with ~20 cm² surface area each.
Combined capacitance equivalent to a sphere of 3.5 m radius.
Theoretical capacity to charge 10 microfarads to the potential of one Daniell cell under 6,000 kg of pressure.
The Curies note that the only practical limitation is the difficulty of applying very high pressures — not any fundamental limit of the crystal itself.
Why This Paper Matters
This paper is the direct ancestor of every piezoelectric device ever built. In it, the Curies:
Established the first piezoelectric measurement standard.
Made the first absolute calibration of a piezoelectric material.
Invented the stacked piezoelectric transducer architecture.
Created a precision instrument that would later be used by Marie Curie to measure radioactivity in her Nobel Prize-winning work.
That last point deserves emphasis. The piezoelectric quartz electrometer described in this paper was the instrument Marie Curie used, fifteen years later, to precisely measure the ionizing power of uranium — work that led directly to the discovery of polonium and radium.
