He has shown that the hammer of a revolver, say
a centre fire, strikes the cartridge at a point which is never the
exact centre of the cartridge, but is always the same for the same
weapon. He has made negatives of bullets nearly a foot wide. Every
detail appears very distinctly and it can be decided with absolute
certainty whether a certain bullet or cartridge was fired by a
certain revolver."
He had picked up one of the microphotographs and was looking at it
attentively through a small glass.
"You will see," he explained, "on the edge of this photograph a
rough sketch calling attention to a mark like an L which is the
chief characteristic of this hammer, although there are other
detailed markings which show well under the microscope but not in
a photograph. You will note that the marks on a hammer are
reversed on the primer in the same way that a metal type and the
character printed by it are reversed as regards one another.
Moreover, depressions on the end of a hammer become raised on the
primer and raised markings on the hammer become depressions on the
primer.
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