In 1951, the Detroit Police Department produced a public relations film titled, This is Your Police Department that provides an early example of governmental promotion of public belief in the myth of the lie detector. As the film follows the training of Joe, a new recruit, the narrator explains that "Joe, with other cadets, found how modern scientific crime detection speeds the work of every department." The narrator then presents the spectrograph and the polygraph as examples. But while spectography is based on sound science, polygraphy is not. By presenting them together, the film creates the false impression that they are similar.

Here are the narration and stills from the polygraph sequence:



Some of the police academy work was fun...



...like the day Joe volunteered to be a guinea pig
for a polygraph, or lie detector test.



Now Joe thought he could fool the machine...



...but when the machine showed he was lying
(just for fun, of course)...



...he readily admitted that the polygraph
had outsmarted him.

Of course, the truth of the matter is that the polygraph cannot detect lies, but depends instead on a misinformed, and in the case of the audience of this film, a disinformed public.

The entire film may be downloaded here:

http://www.archive.org/details/ThisIsYo1951

Interestingly, from watching this film, you would think that in 1951, everyone in Detroit was white. There is not a single non-white face to be seen in this film, as far as I can tell.