Ehrenfried Walther von Tschirnhaus (or Tschirnhausen) (April 10, 1651–October 11, 1708) was a German mathematician who worked in differential geometry. He was born in Kieslingswald and died poor in Dresden. He studied mathematics, philosophy, and medicine at the University of Leiden.
In 1682 he worked out the theory of caustics by reflection, or, as they were usually called, catacaustics , and showed that they were rectifiable. This was the second case in which the envelope of a moving line was determined. He constructed burning mirrors of great power. The Tschirnhaus transformation, by which he removed certain intermediate terms from a given algebraical equation, is well-known; it was published in his Acta Eruditorum in 1683.
Tschirnhaus sought various means of income, such as a paid position at the Académie Royale des Sciences and a new method of producing porcelain. However, he only received an unpaid appointment to the Academy, and guarded his porcelain method from various governments seeking it until his death.
For a short time in 1672 Tschirnhaus enlisted in a student army, but did not fight.
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