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On This Day

  • 10-25-1400

    Geoffrey Chaucer died in London and was buried in Westminster Abbey. Although rightly famous for his Canterbury Tales, he also wrote two astronomical works.

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    Geoffrey Chaucer
  • 10-25-1647

    Evangelista Torricelli died in Florence, Italy. He was an assistant to Galileo during the last few months of Galileo's life and may be best known today for extending Cavalieri's method of indivisibles and for his "trumpet."

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    Evangelista Torricelli
    Galileo Galilei
    Bonaventura Cavalieri
  • 10-25-1713

    Gottfried Leibniz, in a letter to Johann Bernoulli, observed that an alternating series whose terms monotonically decrease to zero in absolute value is convergent. In a letter of January 10, 1714, he gave an incorrect proof. Examination of the proof indicates that it is essentially the one used today, except that Leibniz failed to say anything about the completeness of the real numbers.

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    Gottfried Leibniz
    Johann Bernoulli
    Alternating Series and Leibniz's Test