Philip O. Gravelle

Philip O. Gravelle was an American chemist who, working under the guidance of forensic ballistics pioneer Calvin Goddard, developed a comparison microscope adapted for the identification of fired bullets and cartridge cases. The device joined two microscopes through an optical bridge so an examiner could view two specimens side by side in a single field, allowing direct comparison of the microscopic striae a gun barrel leaves on a bullet rather than relying on memory between separate observations. Gravelle co-founded the Bureau of Forensic Ballistics in New York City with Charles Waite, Goddard and John H. Fisher, and in 1929 he and Goddard used the comparison microscope to help clear the Chicago Police Department of involvement in the Saint Valentine's Day Massacre.