Identifications by comparisons have been made with more or less success for centuries.
The application of precision measurement methods for these purposes is of recent origin and is not generally understood.
This lack of understanding of the principles upon which the science is based is responsible for the confusion so often resulting from evidence introduced in courts of law.
We are so accustomed to the usual methods of description, which are only approximate and by virtue of these approximations are susceptible of no precise interpretations, that we fail to recognize the extreme accuracy of identifications made by precision measurements.
When we say we are looking for a man six feet tall of rather heavy build, with dark hair, with a scar on one hand and with some gold teeth in his mouth we should not be surprised to find several hundred citizens of the United States who meet the description.
If we increase the precision of the description to a man 72% inches tall, weighing 207 pounds, index finger of left hand amputated at the second joint and with gold crowns on left cuspid and right bicuspids, we may feel sure there is not more than one man in the entire country who will meet the specifications, and having found this one, further search cannot be justified without the introduction of some unusual condition.
The justification for this definite conclusion of positive identification is based on the "Law of Probability." Briefly and in non-technical terms this law is interpreted from the fraction which represents the ratio of the number of times a * Communicated by the Director.