William J. Hammer was born in Cressona, Pennsylvania, on February 26, 1858, was an associate of Thomas Edison and an early aviation supporter and enthusiast. He began his career as an assistant to Edward Weston of the Weston Malleable Nickel Company. In 1879, he moved on to a new position as laboratory assistant to Thomas Edison at Menlo Park, New Jersey. His duties ranged from aiding in conducting experiments on such devices as the phonograph, telephone and ore separator to acting as Edison's key person in further developing the incandescent electric lamp. By 1880, he was made chief engineer of the Edison Lamp Works. A year later, Edison dispatched Hammer to London to be chief engineer of the English Electric Light Company. In this position, he helped construct the Holborn Viaduct Central Electric Light Station in London. This was the first central station ever built for incandescent electric lighting. In 1883, Hammer became chief engineer for the German Edison Company. This task included planning and supervising the construction of all Edison plants in Germany. He returned to the United States late in the following year and acted as chief inspector of central stations of the parent Edison Electric Light Company. In 1886-87, Hammer was general manager and chief engineer of the Boston Edison Electric Illuminating Company. In 1888, he worked as an independent engineer and supervised the completion of the then-largest isolated electric lighting plant, located at the Ponce de Leon Hotel in St. Augustine, Florida. During that year, Hammer also was chosen as consulting electrical engineer to the Cincinnati Centennial Exposition. Subsequently, Edison selected him as his personal representative to the Paris Exposition of 1889. This assignment rounded out Hammer's eleven years with Edison. During his time as one of Edison's most trusted and important employees, Hammer devised a number of innovations to the incandescent electric lamp. He designed and built the first electric sign, which spelled out the name "Edison". While in Germany, he invented the automatic motor-driven flashing electric lamp sign. This particular sign flashed the word "Edison" letter by letter and then all at once. At the International Electrical Exhibition, held in Philadelphia in 1884, Hammer also constructed the first flashing column of electric lights.
Upon his return to the U.S. in 1890, Hammer worked as an independent consulting electrical engineer by assisting in a variety of electrical projects, carrying out tests, giving lectures and providing expert testimony in patent disputes. He based this modest enterprise in an office in New York City and continued in this occupation until 1925. His career as an electrical engineering consultant was interrupted by World War I. In June 1918, he was commissioned a major in the U.S. Army. He was assigned to the Inventions Section of the War Plans Division of the General Staff in charge of Aeronautical and Electrical Inventions at the Army War College, Washington, D.C.. By December of that year, he was attached to the Operations Division General Staff at the War Department (Inventions Section). During the war and on into 1919, Hammer also worked for the U.S. Patent Office by identifying any aviation-related patents likely to convey too much information to potential enemies. In conjunction with his War Department duties, he acted as a member of the Advisory Board of Experts affiliated with the Alien Property Commission.
Busy as he was with his private consulting work, Hammer also immersed himself in other scientific activities. He took a particular interest in radium after visiting Pierre and Marie Curie in Paris in 1902. The two discoverers of radium gave him some samples of this substance. Soon after returning to the United States, Hammer experimented with radium. His research yielded numerous useful applications for this material such as radium-luminous powders and paints that were used to coat everything from watch and clock dials to aeronautical instruments, switches and toys. Hammer also advocated the use of radium for cancer and tumor treatment. Beyond his interest in this material, he invented selenium light-sensitive cells and recommended many practical uses for them. He also conducted a great deal of laboratory work on X-rays, ultraviolet and cathode rays, phosphorescence and wireless communications. Accordingly, he lectured and published extensively on many of these fields of research and study.
Hand in hand with his overall interest in science and technology, Hammer had a particular passion for aeronautics. Beyond paying careful attention to the rapid progress made in this field at the turn of the twentieth century, he also played an active role as participant and supporter. He made his first balloon flight over France during the Paris Exposition of 1889. His last lighter-than-air journey took place in 1931 aboard the U.S. Navy dirigible Los Angeles. Moreover, he attended and officiated over many balloon, airship and airplane exhibitions and races. Hammer was a member of the Aero Club of America and a director of the Aeronautical Society. This latter group made the first ever purchase of an airplane in January 1909. He served as expert and secretary of the Aeronautics Committee on the Hudson-Fulton Celebration Commission of 1909 and wrote the contracts for Wilbur Wright and Glenn Curtiss to fly their airplanes for this event. This occasion in New York was important as it marked the first time a large gathering of people in the U.S. witnessed heavier-than-air powered flight. As a friend of the Wright brothers, Hammer testified as an expert witness on their behalf during various patent litigation suits. His contact with aviation pioneers went beyond the Wrights and Curtiss. He also knew and interacted with, among others, Samuel Langley, Alberto Santos-Dumont, Henri Farman and Count Ferdinand von Zeppelin. Even his work with radium had applications for aviation. Hammer developed radium-based luminous compounds and used them on aircraft instruments so pilots could more easily view their cockpits' dials and gauges.
Hammer's last years were filled with serving as Historian General of the Military Order of the World War, as well as participating in many scientific, engineering and aeronautical committees and societies. During this time, he was the recipient of numerous honors and awards, including the Elliott Cresson Gold Medal, John Scott Medal from the Franklin Institute and the Cross of the Legion of Honor from France. Up until his death on March 24, 1934, he also labored in his efforts to organize a vast personal collection of rare and valuable scientific artifacts, photographs and other materials accumulated since his days with Edison. Following Hammer's death, this important collection was left in the care of his daughter Mabel (his wife of twelve years, Alice, having died in 1906). Some years later, International Business Machines (IBM) acquired it. In 1962, IBM donated the William J. Hammer Scientific Collection to the Smithsonian Institution. The bulk of the collection resides with the National Museum of American History's Archives Center. In the mid 1980s, the aeronautical portion of this collection was transferred to the National Air and Space Museum (NASM) Archives.