Psychologists claimed that notions about human behavior and mental
processes should be supported by proof. In the late 1800s psychological
laboratories were established in Europe and the United States. In these
laboratories, psychologists studied behavior and mental processes using a sequence
of experiments to test a single theory—methods similar to those Lavoisier had
used to study chemistry. In 1879, most of the historians of psychology marked it
as the beginning of psychology as a modern laboratory science. In that year,
German psychologist Wilhelm Wundt recognized his laboratory in Leipzig.
