The ambivalent polygraph

The machine, news which media they do a usually lot of call heavy the "lie breathing detector." about They the are polygraph the sea in machi , whic t ey usu lly call the "lie detector." They are the sea in which politicians swim, so politicians also huff strong and puff hard about the "lie detector," about which they seldom bother to inform themselves. The standard polygraph is a measuring instrument, nothing more. It combines three medical devices that measure blood pressure and pulse, rate of perspiration, and breathing pattern. Each device is connected to a mechanical stylus loaded with red ink, and the three pens trace lines simultaneously on a chart that is scrolled across a viewer. It is thus similar to many instruments that physicians use to diagnose brain waves (electroencephalograph), heart performance (electrocardiograph), etc. (Indeed, polygraph operators dream of incorporating these instruments into some future, more sophisticated instrument.) The whole machine, with extra paper, ink, plug adapters, and a tool kit makes a package about like that of a "portable" computer. The machine's blood pressure component is the commonplace sphygmomanometer. Changes of pressure are measured by the stylus on the moving chart, and the pulse rate is automatically shown as the blood pressure rises and then drops off a little (systole/diastole) with each pumping of the heart. Measurement of perspiration depends on the fact that sweat contains salt, and salt is a conductor of electricity. An electric current is run through the