A memoir on finite differences, written when Poisson was 18, attracted the attention of Legendre . However, Poisson found that descriptive geometry, an important topic at the École Polytechnique because of Monge, was impossible for him to succeed with because of his inability to draw diagrams.
Ang isang talaarawan sa wakas pagkaka-iba, nakasulat na kapag Poisson ay 18, ating pagsulo ng Legendre. Gayunman, Poisson natagpuan na naglalarawan geometry, isang mahalagang paksa sa École Polytechnique dahil sa Monge, ay hindi maaari para sa kanya upang magtagumpay sa dahil sa kanyang kawalan ng kakayahan upang maglabas ng diagram.