Carl Theodore Heisel
Pseudo-mathematician (1852–1937)
Carl Theodore Heisel (1852–1937) was a mathematical crank who wrote several books in the 1930s challenging accepted mathematical truths. Among his claims is that he found a way to square the circle. He is credited with 24 works in 62 publications. Heisel did not charge money for his books; he gave thousands of them away for free. Because of this, they are available at many libraries and universities. Heisel's books have historic and monetary value. Paul Halmos referred to one of Heisel's works (a book claiming to have accomplished the impossible task of squaring the circle) as a "classic crank book."
Selected works
Heisel, Carl Theodore (1934). Mathematical and geometrical demonstrations, disproving numerous theorems, problems, postulates, corolleries, axioms naturally growing out of the extraordinary discoveries of a lacking link (2d. ed.). Cleveland.
The public source identifies “Carl Theodore Heisel” as pseudo-mathematician (1852–1937). This brief keeps that definition visible, then builds a research path around Carl, Theodore and Heisel.
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Chronology provides the most reliable spine for this subject; interpretation should follow only after identities and dates are secure. The source revision retrieved here is dated Feb 11, 2026. The linked authority identifier is Q64374352. VIAF identifies the subject as 58752724. The Library of Congress control number is no2002070146. 1 of 3 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank. The first chronological checks are 1852, 1937 and 1934.
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This entry incorporates text from “Carl Theodore Heisel” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.