Compound lever the force of pushing back the stick to the levers and they rub against the wheels, using friction to slow and eventually stop the train. These are everyday applications of this mechanism. A piano key is a compound lever of the first-class, since the fulcrum is between the weight to be moved and the power. The purpose of this lever is to translate a small movement (depression of the key) into a larger and fast movement of the hammer on the strings. The quality of the resulting tone depends on whether the final speed is brought about by gradual or
Jan Lever by the Reformational philosophy of philosopher Herman Dooyeweerd. During his student days, Lever became acquainted with the biologist Johann Heinrich Diemer, who had published about Dooyeweerd's approach in the domain of biology in the 1930s. Diemer was a great influence on Lever's thought. Together with Dooyeweerd, Lever wrote four articles about the species concept in the journal "Philosophia Reformata" (1948–1950) in which species were defined as constant types. In his book, "Creatie en Evolutie" (1956), Lever still subscribed to Dooyeweerd’s philosophy but also suggested that it is possible that biological evolution occurred. Later he moved away from these earlier ideas