Microscope, comparison

It has been noted that "No new methods of fired bullet identification have been adopted since utilization of the comparison microscope over forty years ago" (5). Does the information revealed in the L.E.A.A. survey (2) that the area of firearms comparison was among those with the lowest number of degree holders suggest contributing factors for the lack of scientific advancement in that field ... 

Ever since the introduction of the comparison microscope into the field of advanced firearms indentification in about 1925, people engaged in this work have been processing ballistics evidence, bullets and shells, in exactly the same manner. This can only be done by examining each piece of evidence separately and individually, one piece at a time, and comparing this evidence, again separately and individually, by the utilization of the comparison microscope. Today, we in the field of firearms identification still process evidence in exactly the same manner using the same techniques and basically the same instrument that was applied almost fifty years ago. 

Surface-analyzing (or contour-analyzing) methods are a completely different approach in the examination of firearms evidence. They do not duplicate or replace the comparison microscope. 

Surface analyzing techniques aim at being able to reproduce not only striae, but all surface phenomena, including ridges and valleys whose slopes are too gradual to show up under the comparison microscope, and to be able to compare not patterns of light and shade but actual three-dimensional surfaces. 

Everyone involved with these various proposals realizes the urgent need for a more modern system than that currently in use. The use of the comparison microscope, and the direct optical comparison in split-field observation of each and every separate piece of evidence is a tremendously time-consuming process. It also requires the physical presence of all evidence and test specimens. The circulation of evidence specimens for comparison with evidence or tests on file in other cities is also a very costly and time-consuming process, not to mention the problems that can arise in maintaining the continuity in the chain of possession of evidence. Presently, each comparison requires a manual search through the ballistics evidence files. This requires time, personnel, and a great deal of space devoted to the storage of evidence files. 

A polarizing comparison-microscope for use in petrographic measurements. U. S. Bur. Mines Rept. Investigations 3503. 

Rgure 1 Comparison microscope with camera system. (Courtesy of Leica.)... 

Additional microscopes include the comparison microscope that permits the microscopist to look at two specimens side by side. This is a usefiil early step in the comparison of two fibers or paint chips believed to have originated from the same source. The items can be observed and photographed side by side, permitting detailed scrutiny by both the forensic scientist and the court. Other light microscopes such as fluorescence, hot stage, phase contrast, and interference instruments may be of value in certain investigations, as shown in Table 1. 

Comparison microscope Side-by side viewing Diameter, color, pigment, and/or delustrant density and distribution... 

Stoney, D. A., and P. M. Dougherty. "The Microsct in Forensic Science Forensic Microscopy in the 1890s and the Development of the Comparison Microscope," in R. Saferstein, ed.. More Chemistry and Crime From Marsh Arsenic Test to DNA Profile. Washington, DC American Chemical Society, 1997. 

The severely degraded cellulose acetate fibers bore little resemblance to the nondegraded fibers. Consequently, it would be impossible for a forensic scientist to match the degraded and undegraded fibers using a comparison microscope. No conclusions could therefore be drawn as to whether the two fibers could have had a common origin. 

Each month for six months the hair specimens contained in one of the pots were carefully exhumed. Excess soil was brushed from the samples, any evidence of growth on the bags or hairs was noted and several hairs from each subsample were permanently mounted on a microscope slide using Per-mount (Fisher Scientific). The hairs were examined with a Leitz Dialux comparison microscope, with magnifications ranging from 50X to 500X. The exhumed hairs were compared with standard hairs from the same sample. 

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