EULER, Leonhard. Methodus inveniendi lineas curvas maximi minimive proprietate gaudentes, sive solutio problematis isoperimetrici latissimo sensu accepti. Lausanne and Geneva: M.-M. Bousquet, 1744. 4o. Title printed in red and black, engraved title vignette, 5 engraved folding plates, woodcut head-piece and initial. Contemporary vellum, lettering piece on spine (some staining to upper cover). Provenance: Initials "DSA" (early ink stamp on title); Janus Foundation, San Francisco (bookplate). FIRST EDITION of Euler's most valuable contribution to mathematics in which he developed the concept of the calculus of variations. Dibner Heralds of Science 101; Grolier/Horblit 28; Norman 731.