Lever force F at a point "A" located by the coordinate vector r on the bar. The lever then exerts an output force F at the point "B" located by r. The rotation of the lever about the fulcrum "P" is defined by the rotation angle "θ" in radians. Let the coordinate vector of the point "P" that defines the fulcrum be r, and introduce the lengths which are the distances from the fulcrum to the input point "A" and to the output point "B", respectively. Now introduce the unit vectors e and e from the fulcrum to the point "A"
Jan Lever evolutie" (1956; English translation 1958 under the title "Creation and Evolution"). In 1970, Lever was elected member of the Royal Netherlands Academy of Arts and Sciences. In the early 1950s, Lever started research on the neuroendocrine system of the basommatophoran snail, "Lymnaea stagnalis". Lever himself found a particular kind of neurons in the ancylid snail "Ferrissia", and his student Joos Joosse demonstrated those neurons in other snail species. "Lymnaea" became the animal of choice for physiological research at the VU Amsterdam laboratory for decades. At the beginning of his career, Lever’s ideas about evolution and the species concept were inspired