TRAFFIC LIGHTSInventor: William PottsYear, place: 1920, Detroit, Michigan (United States)Definition: A traffic light is a device that is designed to control the flow of traffic by using three colored lights.Then and now: The initial idea for the traffic light came from Potts experience working as a police officer directing traffic. The invention itself reduced the workload of policemen by eliminating the dangerous job of controlling busy intersections. Nearly a century later, the traffic light remains as central to the life and safety of drivers and pedestrians as it ever was.A policeman in an intersection before the apparition of the traffic lights

LIE DETECTOR/POLYGRAPHInventor: John A. LarsonYear, place: 1921, CaliforniaDefinition: A polygraph measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while the subject is asked and answers a series of questions.Then and now: John A. Larsons polygraph was used extensively, and with much success, in criminal investigations. Benefiting from more than a century of research, development and widespread use, the polygraph examination remains the most effective means of verifying the truth and detecting deception.

John Larson's "Cardio-Pneumo Psychograph" in action.

The basic components of a (digital) lie detector system

John Larson in 1921