Henri Poincaré, The Moral Union

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(This allocution was delivered by Henri Poincaré at the inaugural meeting of the French League of Moral Education on June 26, 1912, three weeks before his death. This is the last time he has spoken in public.) Today’s Assembly brings … Read More

Henri Poincaré, Morality and Science

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In the last half of the nineteenth century, we often dreamed of creating a scientific morality. It was not enough to boast the educative virtue of science, the advantages which the human soul derives for its own perfecting of the … Read More

Henri Poincaré, Reports on Matter and Ether

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(Conference at the French Society of Physics, April 11, 1912.) When Mr. Abraham came to ask me to close the series of lectures organized by the French Society of Physics, I was at first about to refuse; it seemed to … Read More

Henri Poincaré, Quanta hypothesis: Conclusions

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We see what is the state of the question; the ancient theories, which hitherto seemed to account for all known phenomena, have encountered an unexpected obstacle. It seemed that a modification was necessary. A hypothesis was first presented in Mr. … Read More

Henri Poincaré, Quanta hypothesis: The ideas of Mr. Sommerfeld

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Mr. Sommerfeld has proposed a theory which he wants to relate to that of Mr. Planck, although the only connection between them is that the letter h appears in both formulas, and that the same name of quantum of action … Read More

Henri Poincaré, Quanta hypothesis: The new theory of Planck

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Let us go back to less general and more precise problems, for example to the theory of radiation. Mr. Planck has devised an amendment to his first theory, and I would like to say a few words about it. According … Read More

Henri Poincaré, Quanta hypothesis: Quanta of action

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The new design is seductive by a certain side; for some time the tendency has been to atomism, matter appears to us as formed of indivisible atoms, and the electricity is no longer continuous, it is no longer divisible to … Read More

Henri Poincaré, Quanta hypothesis: More on quanta of energy

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Statistical equilibrium can only be established if there is exchange of energy between the resonators, otherwise each resonator would retain its initial energy, which is arbitrary, indefinitely, and the final distribution would obey no law. This exchange could not be … Read More

Henri Poincaré, Quanta hypothesis: Quanta of energy

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The explanation of these phenomena must be sought without making a clean sweep of the principles of Thermodynamics; above all, we must admit the possibility of statistical equilibrium, otherwise nothing would remain of Carnot’s principle; we cannot admit, in Thermodynamics, … Read More

Henri Poincaré, Quanta hypothesis: The law of radiation

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Physicists did not at first concern themselves with these difficulties, but two new facts changed the face of things; the first is what is called the law of black radiation. A perfectly black body is one whose absorption coefficient is … Read More

Henri Poincaré, Quanta hypothesis: Thermodynamics and probability

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Let us go back to the kinetic theory of gases; the gases are formed of molecules which circulate in all directions with great velocities; their trajectories would be rectilinear if from time to time they did not collide each other, … Read More

Henri Poincaré, Quanta hypothesis

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One wonders if Mechanics is not on the eve of a new upheaval; recently a meeting was held at Brussels, attended by some twenty physicists of various nationalities, and at each moment they might have been heard to speak of … Read More

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