Johann Heinrich Lambert (German: [ˈlambɛɐ̯t]; French: Jean-Henri Lambert; 26 or 28 August 1728 – 25 September 1777) was a polymath from the Republic of Mulhouse, generally identified as either Swiss or French, who made important contributions to the subjects of mathematics, physics (particularly optics), philosophy, astronomy and map projections.

Lambert was born in 1728 into a Huguenot family in the city of Mulhouse[1] (now in Alsace, France), at that time a city-state allied to Switzerland.

On his return to Chur he published his first books (on optics and cosmology) and began to seek an academic post.

After a few short posts he was rewarded (1763) by an invitation to a position at the Prussian Academy of Sciences in Berlin, where he gained the sponsorship of Frederick II of Prussia, and became a friend of Euler.

[6] Lambert also devised theorems about conic sections that made the calculation of the orbits of comets simpler.

That is, the area of a hyperbolic triangle (multiplied by a constant C) is equal to π (radians), or 180°, minus the sum of the angles α, β, and γ.

The non-SI unit of luminance, lambert, is named in recognition of his work in establishing the study of photometry.

[17] His investigations were built on the earlier theoretical proposals of Tobias Mayer, greatly extending these early ideas.

The Neues Organon contains one of the first appearances of the term phenomenology,[20] and it includes a presentation of the various kinds of syllogism.

According to John Stuart Mill, The German philosopher Lambert, whose Neues Organon (published in the year 1764) contains among other things one of the most elaborate and complete expositions of the syllogistic doctrine, has expressly examined which sort of arguments fall most suitably and naturally into each of the four figures; and his investigation is characterized by great ingenuity and clearness of thought.

Shortly afterward, Lambert published his own version of the nebular hypothesis of the origin of the Solar System in Cosmologische Briefe über die Einrichtung des Weltbaues (1761).

Lambert propounded the ideology of observing periodic phenomena first, try to derive their rules and then gradually expand the theory.