Philip O. Gravelle

Born: in 1891

Died: 1955

In the 1920s, Phillip O Gravelle was born in 1891. After the Valentine’s Day Massacre, Calvin Goddard and Philip O. Gravelle worked with the police using their comparison microscope, and Phillip O Gravelle died in 1955. Phillip O Gravelle was Calvin Goddard’s partner, and he was in New York during Valentine’s Day Massacre in the 1920s. Phillip O Gravelle and his associate Calvin Goddard invented the comparison microscope, which revolutionized forensics by allowing scientists to identify discharged bullets and cartridges using the microscope. Phillip O Gravelle is significant in the field of forensics because he invented the comparison microscope, which allowed scientists to identify discharged bullets. Philip O Gravelle invented the comparison microscope in the 1920s in New York during the valentines day massacre.


The Bureau of Forensic Ballistics was founded in New York City by Charles E. Waite, Calvin H. Goddard, Philip O. Gravelle, and John H. Fisher. The Bureau was established to provide nationwide gun identification services. Goddard headed the bureau after Waite died in 1926 until it was abolished in 1929.

In the subject of guns identification, Gravelle and Goddard used comparative microscopy. This made it easier for the examiner to find matching striae. The heliometer, a magnifying probe used to view the interior of firearm barrels and accurately determine the pitch of rifling, was invented by Goddard and Fisher. Its obsolescence was due to its limited application.

The Saturday Evening Post ran a two-part feature titled “Fingerprinting Bullets — The Silent Witness” in June 1925. These articles had an important role in enlightening the public about both the science of firearm identification and the Bureau of Forensic Ballistics’ services.


For the Los Angeles County sheriff, Captain Edward C. ‘Ned’ Crossman, a well-known shooter and journalist, investigated guns evidence. He became a regional representative for the Bureau of Forensic Ballistics in the western United States.


The conclusions of the Sacco and Vanzetti case were reviewed by a special committee. Colonel Calvin Goddard reexamined retrieved evidence bullets and cartridge cases using a comparison microscope and heliometer (latest technological developments previously unavailable). He was able to confirm that Sacco’s weapon had fired one fatal bullet and one cartridge case. Following reexaminations in 1961 and 1983, these findings were confirmed.


The St. Valentine’s Day Massacre (February 14, 1929, Chicago, Illinois), which sparked widespread public outrage and accusations that police officers were implicated, prompted local officials to appoint a grand jury to investigate the slaying of seven gangsters by a rival gang.

Calvin H. Goddard of the Bureau of Forensic Ballistics was hired by the grand jury foreman to analyze firearms-related evidence, which included fired bullets, pellets, discharged shotshell cases, and fired cartridge cases. The killers utilized one 12-gauge shotgun and two Thompson submachine guns, according to Goddard. He pointed out that one of the Thompson submachine guns used a fifty-round drum magazine, while the other used a twenty-round magazine.

All police Thompson submachine guns were tested, and the results were compared to the crime scene evidence. He established that none of the police weapons were used in the deaths, and he later identified the murder weapons as firearms recovered during a search of a suspect’s residence.

Valentine’s Day Massacre


Phillip O. Gravelle was a partner with Colonel Goddard in the 1920s, and they utilized the comparison microscope to show the Chicago Police Department’s innocence in the St. Valentine’s Day Massacre case. In 1929, the St. Valentine’s Day Massacre occurred, when seven members and associates of Chicago’s North Side Gang were murdered. It took place at Lincoln Park, Chicago, Illinois, United States, at the Warehouse at Dickens and Clark.

Change to History

The invention of the comparative microscope was Gravelle’s contribution to forensic science. Scientists were able to utilize it to identify bullets and cartridges, which changed history. This made identifying bullets considerably easier, as it revealed what type of pistol the bullet was fired from.

Contribution Details

The invention of the comparative microscope was Phillip O. Gravelle’s contribution to forensic science. The Sacco and Vanzetti case was one of the first to apply his invention. Gravelle invented the microscope, although he had the backing and assistance of his associate Calvin Goddard.

  • The Comparison Microscope was invented in New York in the 1920s.
  • To compare animal hairs, we use the Comparison Microscope.

A comparison microscope is a device that allows you to compare two specimens side by side. It is made up of two microscopes joined by an optical bridge, resulting in a split view window that allows two different objects to be observed at the same time. When comparing two items under a typical microscope, this eliminates the need for the viewer to rely on memory.

With the help and advice of forensic ballistics pioneer Calvin Goddard, chemist Philip O. Gravelle created a comparison microscope for use in the identification of discharged bullets and cartridge cases. It was a big step forward in forensic science’s understanding of guns identification.

The unique striae left on the bullet or cartridge case are compared to the worn, machined metal of the barrel, breach block, extractor, or firing pin in the rifle to identify the firearm from which the bullet or cartridge case was discharged. Gravelle was the one who doubted his recall. “Scientific precision could not be achieved as long as he could only inspect one bullet at a time with his microscope and had to remember the image of it until he placed the comparison bullet under the microscope. As a result, he created the comparative microscope, which Goddard put to use.” The comparative microscope was perfected by Calvin Goddard, who popularised its use.

Sir Sydney Smith agreed, highlighting the usefulness of the concept in forensic science and firearms identification. He brought the comparison microscope to Scotland and showed it to European experts who needed it for guns identification and other forensic science applications.

Modern Comparison Microscope

Fiber optic illumination, video capabilities, digital imaging, automatic exposure for conventional photography, and other optical, mechanical, and electronic enhancements are included in the modern equipment. Despite this evolution, the basic tools and techniques for determining whether or not ammunition components were fired by a single firearm based on unique and repeatable microscopic and class characteristics, or for reaching a “no conclusion” result if insufficient marks are present, have remained unchanged.

Modern Comparison Microscope

Law enforcement agencies have created forensic laboratories, researchers have learned much more about how to match bullets and cartridge cases to the guns used to shoot them, and comparison microscopes have become more advanced since then. Ballistic identification has become a well-established sub-specialty of forensic science by the end of the 1980s.

Visualization techniques have also been developed to assist a firearms expert to verify the degree of similarity between two tool-marks. These are meant to imitate the operation of a comparison microscope and can render a 2D picture of 3D surfaces in the same way that a traditional comparison microscope can.

Forensic Ballistics

The invention of the comparison microscope was inspired by the high prevalence of handgun-related crime in the United States compared to most other developed countries. The fired ammunition components, like most firearms, may develop enough unique and reproducible microscopic markings to be identified as having been fired by a single firearm. Making these comparisons is known as firearms identification, or “ballistics” in some cases.

This forensic discipline has always required a forensic expert to perform a microscopic side-by-side examination of fired bullets or cartridge cases, one pair at a time, to confirm or rule out the two items as having been discharged by a single firearm. For this purpose, the traditional tool of the firearms examiner has been what is often called the ballistics comparison microscope.

The interior of a gun’s barrel is machined with grooves (referred to as rifling) that cause the bullet to rotate as it goes down the barrel. These grooves, along with their “lands” counterparts, imprint grooves and land impressions on the bullet’s surface. Imperfections on the barrel surface are accidentally transferred to the bullet’s surface, along with these land and groove impressions. Because these flaws occur at random during the manufacturing process or as a result of use, they are unique to each barrel. As a result, these patterns or defects become a “signature” that each barrel imprints on each bullet fired through it.

The “signature” on the bullets imparted by the distinctive defects on the barrel allows bullets to be validated and identified as having originated from a specific pistol. The matching of microscopic impressions observed on the surface of bullets and casings is examined using a comparison microscope. When forensic examiners recover a firearm, a bullet, or a cartridge case from a crime scene, they compare the ballistic fingerprint of the recovered bullet or cartridge case to the ballistic fingerprint of a second bullet or cartridge case test-fired from the recovered firearm.

Investigators know the recovered bullet or cartridge case was fired from the recovered gun if the ballistic fingerprint on the test-fired bullet or cartridge case matches the ballistic fingerprint on the recovered bullet or cartridge case.

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