Thirty-three years after Saccheri's publication, John Heinrich Lambert (1728-1777) of Germany wrote a similar investigation entitled Die Theorie der Parallellinien, which, however, was notpublished until after his death. Lambert chose a quadrilateral containing three right angles (half of aSaccheri quadrilateral ) as his fundamental figure, and considered three hypotheses according as the fourth angle is acute, right, or obtuse. He went considerably beyond Saccheri in deducing propositions under the hypotheses of the acute and obtuse angles. Thus, with Saccheri, heshowed that in the three hypotheses the sum of the angles of a triangle is less than, equal to, or greater than two right angles respectively, and then, in addition, that the deficiency below two right angles in the hypothesis of the acute angle, or the excess above two right angles in the hypothesis of the obtuse angle, is proportional to the area of the triangle.