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1800

Lacroix completes publication of his three volume textbook

1801

Gauss publishes *Disquisitiones Arithmeticae* (*Discourses on Arithmetic*). It contains seven sections, the first six of which are devoted to number theory and the last to the construction of a regular 17-gon by ruler and compasses.

1801

The minor planet Ceres is discovered but then lost. Gauss computes its orbit from the few observations that had been made leading to Ceres being rediscovered in almost exactly the position predicted by Gauss.

1801

Gauss proves Fermat's conjecture that every number can be written as the sum of three triangular numbers.

1803

Lazare Carnot publishes *Géométrie de position* in which sensed magnitudes are first used systematically in geometry.

1804

Bessel publishes a paper on the orbit of Halley's comet using data from Harriot's observations 200 years earlier.

1806

Argand introduces the Argand diagram as a way of representing a complex number geometrically in the plane.

1806

Legendre develops the method of least squares to find best approximations to a set of observed data.

1807

Fourier discovers his method of representing continuous functions by the sum of a series of trigonometric functions and uses the method in his paper *On the Propagation of Heat in Solid Bodies* which he submits to the Paris Academy.

1808

Germain makes an important contribution to Fermat's last theorem. This is named "Germain's theorem" by Legendre.

1809

Poinsot discovers two new regular polyhedra.

1809

Gauss describes the least-squares method which he uses to find orbits of celestial bodies in *Theoria motus corporum coelestium in sectionibus conicis Solem ambientium* (*Theory of the Movement of Heavenly Bodies*).

1810

Gergonne publishes the first volume of his new mathematics journal *Annales de mathématique pures et appliquées* which became known as *Annales de Gergonne*.

List of mathematicians alive in 1800.

List of mathematicians alive in 1810.

JOC/EFR August 2001
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