Policemen Inventors.

In the early 1920s John Augustus Larson, a Berkeley, California, police officer, developed the first practical polygraph. With three pens swinging back and forth on a slowly moving strip of paper, it worked like a seismograph to record changes in the subject's blood pressure, heart rate, and breathing rate. Larson's fellow police officer Leonarde Keeler added a fourth measurement. Increases in perspiration were detected by measuring the "galvanic skin response." An electric current passing over the skin gains strength when salty water (a good conductor) appears on the skin surface. Because these indicators were supposed to increase when a subject lied, the moving pens were supposed to swing more widely when untruths were uttered.

Doubters.

The inventors never claimed that their machine was infallible, and many skeptics have maintained that a person being examined would be so nervous that many false...