 The concept of infinitesimal had arisen with problems of a geometric character and infinitesimals were originally conceived as belonging solely to the realm of continuous magnitude as opposed to that of discrete number. But from the algebra and analytic geometry of the sixteenth and seventeenth centuries there issued the concept of infinitesimal number. The idea first appears in the work of Pierre de Fermat (1601–65) on the determination of maximum and minimum (extreme) values, published in 1638 (Boyer 1939 [1959: 155]).