Some police departments substitute for evidence the "third degree." It is illegal. Law courts could now supplement oral evidence with a "fourth degree"--the lie detector. It should be legal, when properly operated, when its results are properly introduced and weighed.
Any symposium on evidence ought to include some observations on cross-examination. A 'consideration of the instruments employable in the art of cross-examination should, of course, include a discussion of the instrument, the accepted use of which, some lawyers, and certainly the average layman, believe would make cross-examination unnecessary as to credibility.
The best legally available "lie detector" presently is a thorough and searching cross-examination by adept counsel. Most experienced trial judges, therefore, do not attempt to curb relevant cross-examination, although some argumentative and emphatic leading questions are accepted tools of the trade.
Jack Streeter and Melvin M. Bell,
The "Fourth Degree": The Lie Detector,
5 Vanderbilt Law Review
Available at: https://scholarship.law.vanderbilt.edu/vlr/vol5/iss3/13