Preface. XI - XV

French copied from this text in blue

English translations by DeepL in black

Ce Volume de six cents pages represente 1’ensemble de 1’ oeuvre accomplie pendant une vie de travail de plus de vingt-cinq ans. J’espere que ceux qui le liront reconnaitront dansles Memoires qui le composent les traits caracteristiques de la mentalite de leur auteur, et qu’ils n’auront pas de peine a comprendre comment une oeuvre aussi considerable peut se trouver renfermee dans cet unique Volume. Le lecteur n’y trouvera en effet rien de superflu ; on y rencontre bien rarement des superpositions ou des repetitions ; on n’y trouve ni discussions confuses ou peu utiles, ni descriptions detaillees de toutes les experiences executees. Seules sont decrites et exposees dans chaque Memoire les experiences qui conduisent a des resultats clairs et bien etablis, et l’auteur evite avec soin tout abus dans les conclusions. Je n’en puis citer de meilleur exemple que le Memoire sur le magnetisme, si riche en resultats experimentaux, etdont les conclu¬ sions theoriques tres limpides, en vue desquelles d’ailleurs le travail a ete entrepris, sont enoncees d’une maniere aussi sobre que possible dans la seconde moitie de la page 233 du present Volume. De meme dans les Memoires theoriques, seuls ont ete presentes les raisonnements qui, a force d’etre muris, ont pris une forme pour ainsi dire irreprochable. Dans les deux cas, la forme d’exposition, qu’il voulait claire et simple, est extremement soignee, surtout quand il s’agit d’une definition ou d’une notation.

This six-hundred-page volume represents the entirety of the work accomplished over a career spanning more than twenty-five years. I hope that those who read it will recognize in the memoirs that comprise it the characteristic traits of the author’s mindset, and that they will have no difficulty understanding how such a substantial body of work can be contained within this single volume. Indeed, the reader will find nothing superfluous here; one rarely encounters redundancies or repetitions; there are neither confusing or unhelpful discussions nor detailed descriptions of all the experiments performed. Only those experiments that lead to clear and well-established results are described and presented in each memoir, and the author carefully avoids any overreach in his conclusions. I can cite no better example than the Memoir on magnetism, so rich in experimental results, and whose very clear theoretical conclusions—for the sake of which, moreover, the work was undertaken—are stated as soberly as possible in the second half of page 233 of the present volume. Likewise, in the Theoretical Memoirs, only those arguments have been presented which, having been thoroughly developed, have taken on a form that is, so to speak, beyond reproach. In both cases, the style of presentation, which he intended to be clear and simple, is extremely meticulous, especially when it comes to a definition or a notation.

Le triage scrupuleux du texte, la perfection de la forme, la precision et la clarte des enonces fondamentaux donnent a boeuvre publiee de Pierre Curie un caractere pour ainsi dire classique, et permettent dans bien des cas de faire rentrer certains de ses Memoires dans une redaction plus vaste sans aucune modification.

La concision du texte est surtout remarquahle dans les Memoires theoriques sur les questions d’ordre et la symetrie. Bien que ces Memoires soient courts et presque uniquement composes d’enonces de tlieoremes dont la demonstration est settlement indiquee, la redaction est neanmoins extremement claire, et cela grace au soin constant de mettre en evidence le contenu physique de chaque proposition. Le travail sur la symetrie dans les phenomenes physiques est particulierement caracteristique a ce point de vue, et je ne puis mieux faire qne d’en extraire, a titre d’exemple, l’enonce suivant de la loi de la symetrie :

The meticulous editing of the text, the perfection of its form, and the precision and clarity of its fundamental statements give Pierre Curie’s published work a character that is, so to speak, classical, and in many cases allow some of his memoirs to be incorporated into a larger work without any modification.

The conciseness of the text is particularly remarkable in the theoretical memoirs on questions of order and symmetry. Although these memoirs are short and consist almost exclusively of statements of theorems whose proofs are briefly indicated, the writing is nevertheless extremely clear, thanks to the constant care taken to highlight the physical content of each proposition. The work on symmetry in physical phenomena is particularly characteristic in this regard, and I can do no better than to extract, by way of example, the following statement of the law of symmetry:

Lorsque cerlaines causes produisent certains effets, les elements de symetrie des causes doivent se retroiwer dans les effets produits .

Lorsque certains effets revelent une certaine clissymetrie , cette dissymetrie doit se retrouver dans les causes qui leur onl donne naissance .

La reciproque de ces deux propositions n est pas vraie y au moins praliquement , c est- a- dire que les effets produits peuvent etre plus symetriques que les causes.

C’est la un enonce complet et intuitif de la loi de la syme¬ trie sous son aspect le plus general, qu’il est legitime d’appeler loi de Curie.

When certain causes produce certain effects, the elements of symmetry in the causes must be reflected in the resulting effects.

When certain effects reveal a certain asymmetry, this asymmetry must be found in the causes that gave rise to them.

The converse of these two propositions is not true, at least in practice; that is to say, the effects produced may be more symmetrical than the causes.

This is a complete and intuitive statement of the law of symmetry in its most general form, which it is legitimate to call Curie’s law.

Le soin qu’il apportait a eviter dans ses publications toute affirmation et meme toute presomption insuftisamment fondee ne provenait pas uniquement du desir de restreindre la possibilite d’erreurs dans son oeuvre publiee. C’etait la surtout l’babitude d’un esprit soucieux de conserver son independance et sa liberte devant l’imprevu qu’apporte chaque jour la recherche experimental. II s’attachait a considerer toute question a un point de vue tres general, n’adoptant comme base solide que ce qui semblait definitivement acquis ; il ne voulait pas se laisser enchainer par uneidee precongue et aimait envisage r successivement on raeme simultanement diverses possibility experimentales. Lors des discussions qui out eu lieu sur la nature de la radioactivite et bien que nous eumes les premiers enonce les diverses hypo¬ theses possibles, il ne se prononga pour aucune d’entre elles tant que cela lui sembla premature; toutefois il n’en repoussait aucune a priori et executait des experiences diverses pour controler chacune d’elles. Voici comment il s’exprimait dans une Note publiee a cette epoque :

The care he took to avoid in his publications any assertion or even any insufficiently grounded presumption did not stem solely from a desire to limit the possibility of errors in his published work. It was above all the habit of a mind anxious to preserve its independence and freedom in the face of the unexpected that experimental research brings each day. He was committed to considering every question from a very general perspective, accepting as a solid foundation only what seemed definitively established; he did not want to be bound by a preconceived idea and liked to consider various experimental possibilities successively or simultaneously. During the discussions that took place on the nature of radioactivity, and although we were the first to put forward the various possible hypotheses, he did not take a position on any of them as long as it seemed premature to him; however, he did not reject any of them a priori and carried out various experiments to test each one. Here is how he expressed himself in a note published at that time:

« Dans l’etude de phenomenes inconnus on pent faire des hypotheses tres generates et avancer pas a pas avec le concours de Fexperience. Cette marche methodique et sure est necessairement lente. On pent, au contraire, faire des hypotheses hardies oil Fon precise le mecanisme des pheno¬ menes ; cette maniere de proceder a l’avantage de suggerer certaines experiences, et surtout de faciliter le raisonnement en le rendant moins ahstrait par Femploi d’une image. En revanche, on ne peut esperer imaginer ainsi a priori une theorie complexe en accord avec Fexperience. Les hypotheses precises renferment presque a coup sur une part d’erreur a cote d’une part de verite. Cette derniere partie, si elle existe, fait seulement partie d’une proposition plus generate a laquelle il faudra revenir un jour. »

"In the study of unknown phenomena, one can formulate very general hypotheses and proceed step by step with the aid of experience. This methodical and reliable approach is necessarily slow. On the other hand, one can formulate bold hypotheses that specify the mechanism of the phenomena; this approach has the advantage of suggesting certain experiments, and above all of facilitating reasoning by making it less abstract through the use of imagery. However, one cannot hope to conceive a priori a complex theory that is consistent with experience. Precise hypotheses almost certainly contain an element of error alongside an element of truth. This latter element, if it exists, is merely part of a more general proposition to which we will have to return one day.”

Ce passage fait comprendre Fopinion qu ’il avait sur les methodes scientiFiques. Les images trop precises de pheno¬ menes peu connus lui apparaissaient avec les caracteres d’une approximation trop grossiere, et il preferait les eviter. Il s’eflbrgait de se rapprocher progressivement de la conception correcte ; pour cela il cherchait dans des directions variees et ne reculait devant aucune experience susceptible d’eclairer la voie.

This passage reveals his views on scientific methods. Images that were too precise of little-known phenomena struck him as overly crude approximations, and he preferred to avoid them. He took pride in gradually approaching the correct conception; to that end, he explored various avenues and did not shy away from any experiment likely to illuminate the path.

Les Memoires d’ensemble publics par Pierre Curie sont tres peu nombreux, je dirai meme trop peu nomhreux; c’est la encore un resultat de sa methode de travail. II tenait a presenter un sujet d’une maniere tout a fait satisfaisante et ne se pressait pas d’en faire l’expose; il lui arrivait done de se trouver devance par un autre savant s’interessant a la rneme question. Ainsi, par exemple, il n’a jamais ecrit de Memoire d’ensemble sur la piezoelectricite, phenomene qu’il avait decouvert avec son frere, et dont il avait etudie avec lui les caracteres et les circonstances de production d’une maniere aussi complete qu’exacte. La theorie generate de la piezoelectricite a cependant ete publiee par M. Voigt, ce qui amena Pierre Curie a renoncer provisoirement a son projet de publication analogue, et a le retarder jusqu’au moment ou il pourrait faire paraitre le Livre plus complet qu’il preparait sur la theorie des grandeurs dirigees et ses applications a la physique cristalline. Il n’a pu achever ce Livre auquel il tenait beaucoup, mais une partie en a ete completement re¬ digee et a fait l’objet de son enseignement a la Sorbonne en 1900. J’ai Tespoir de completer et de publier ulterieurement ce travail qui a constitue l’une des preoccupations les plus importantes de Pierre Curie pendant ses dernieres annees. Les idees dominantes de cette oeuvre sont celles qui le passionnaient a vingt ans, et au developpement desquelles il a apporte une contribution considerable par la decouverte de la piezoelectricite et par les recherches sur la symetrie dans les phenomenes physiques. Il n’a jamais cesse d’y songer, et, apres sa nomination a la Sorbonne, il a clierche a introduire ces notions importantes dans l’enseignement afm de les repandre davantage. Il esperait ainsi ramener l’interet des physiciens vers les recherches de physique cris¬ talline dont il deplorait souvent Tabandon.

There are very few joint papers by Pierre Curie; I would even say too few; this, too, is a result of his working method. He was committed to presenting a subject in a thoroughly satisfactory manner and did not rush to publish his findings; as a result, he was sometimes beaten to the punch by another scientist interested in the same question. Thus, for example, he never wrote a comprehensive paper on piezoelectricity, a phenomenon he had discovered with his brother, and whose characteristics and conditions of occurrence he had studied with him in a manner as thorough as it was precise. The general theory of piezoelectricity was, however, published by Mr. Voigt, which led Pierre Curie to temporarily abandon his plan for a similar publication and to postpone it until he could release the more comprehensive book he was preparing on the theory of directed quantities and its applications to crystal physics. He was unable to complete this book, which was very dear to him, but a portion of it had been fully drafted and formed the basis of his lectures at the Sorbonne in 1900. I hope to eventually complete and publish this work, which was one of Pierre Curie’s most important concerns during his final years. The central ideas of this work are those that fascinated him at the age of twenty, and to the development of which he made a considerable contribution through the discovery of piezoelectricity and his research on symmetry in physical phenomena. He never ceased to think about them, and, after his appointment at the Sorbonne, he strove to introduce these important concepts into his teaching in order to spread them further. He thus hoped to rekindle physicists’ interest in research on crystalline physics, the neglect of which he often lamented.

La curiosite de son esprit et l’activite de son imagination le poussaient a s’interesser a des sujets extremement varies. 11 aimait s’absorber dans les recherches abstraites de pure theorie, mais il eprouvait aussi un grand plaisir a s’occuper de la construction d’appareils nouveaux ; la plus grande partie de son temps etait generalement consacree aux travaux de recherche experimental .

Ses recherches portent sur le domaine de la Physique et sur celui de la Cristallographie. Ces deux sciences lui etaient egalement familieres et se completaient mutuellement dans son esprit. La symetrie des phenomenes etait pour lui une notion intuitive. D’ailleurs peu de physiciens ont eu autant que lui la connaissance des formes cristallographiques et des groupes de symetrie.

His intellectual curiosity and vivid imagination led him to take an interest in an extremely wide range of subjects. He enjoyed immersing himself in abstract, purely theoretical research, but he also took great pleasure in designing new instruments; most of his time was generally devoted to experimental research.

His research focused on the fields of physics and crystallography. He was equally familiar with both sciences, and they complemented one another in his mind. The symmetry of phenomena was an intuitive concept for him. Indeed, few physicists have had as deep a knowledge of crystallographic forms and symmetry groups as he did.

Bien que ne s’etant jamais occupe de recherches de nature chimique, il n’hesita pas a s’engager dans cette voie quand cela lui parut necessaire, et a entreprendre un long travail de recherche d’elements nouveaux avec une confiance que le resultat a pleinement justifiee. La variete de ses travaux apparait encore plus grande que ne le montre le present Volume quand on se trouve au courant des recherches qu’il n’a pas publiees, ne les ayantpas menees assez loin a son gre.

Although he had never previously engaged in chemical research, he did not hesitate to embark on this path when it seemed necessary, and to undertake a lengthy investigation into new elements with a confidence that the results fully justified. The scope of his work appears even broader than this volume suggests when one becomes aware of the research he did not publish, having not advanced it as far as he would have liked.