Clarence Dally: a technician in trouble

Clarence M. Dally

Published in The Journal – the journal of the IST Autumn 2018

X-rays may be invisible to the human eye, but they have allowed us to see beyond the capabilities of the human eye. They have shown us the atomic structure of materials, the inside of the human body, and they have enabled us to see deep into the universe. X-rays were discovered several times from 1785 onwards until Wilhelm Roentgen made a thorough study of their properties, winning the Nobel prize in 1901. He also took the first X-ray image of a person—the now famous image of his wife’s hand (Figure 1)—but he never patented his discovery and died in poverty.

When Thomas Edison heard of these mysterious rays, he set about a series of experiments with his highly skilled glass blower assistant Clarence Dally, looking at methods of harnessing X-rays to produce a new kind of electric light. The unfortunate result of these experiments was that Dally became the first death recorded as caused by X-ray exposure at the age of just 39.

Dally was born in 1865, the final year of the American Civil War, in Woodbridge, New Jersey, and grew up in a country struggling to heal from the wounds of that war. His father Charles worked as a glass blower at the Edison Lamp Works in nearby Harrison. It may have been stories of the Civil War which led to his enthusiastic enlistment in the Navy as a chief gunner’s mate aged 17. In an interview many years later Dr W.B. Graves, who would become one of Clarence’s surgeons, described Dally as, “a wiry chap, as hard as nails; a little fellow, but a specimen of perfect manhood when he left the United States Navy.” [1] Dally served six years before he was honourably discharged.

Returning home to Woodbridge in 1888, Dally started working with his father and three brothers at the Edison Lamp Works. The 1880s was a great time to be a glass blower as Edison had only recently developed a commercial lightbulb and the early designs required many skilled glass blowers in their production. Dally trained under his father and showed great skill and dexterity in the delicate art of glass manipulation and in the difficult process of “sealing-off” incandescent lightbulbs. Edison, a regular visitor to the factory floor, recognised Dally’s skills and transferred the now 24-year-old Dally to the West Orange laboratory to assist in Edison’s experiments on incandescent lamps.

First X-ray of a person by Wilhelm Röntgen
Figure 1: First X-ray of a person by Wilhelm Röntgen of his wife Anna Bertha Ludwig’s hand showing her wedding ring.

It was only a few years later, in the last few days of 1895, that Wilhelm Conrad Roentgen delivered his preliminary report entitled “On A New Kind of Rays” to the Wurzberg Physical Medical Society [2]. In a matter of weeks the news spread across the world and “Roentgen mania” enveloped scientists, inventors, journalists, and the general public, all of whom speculated on the potential impact of this revolutionary discovery. Concerns about the dangers of X-rays were also quickly raised but such was this mania that many workers ignored the warnings, convincing themselves that the tissue damage reported by various researchers was caused by other effects [3].

Roentgen had used both photographic plates and fluoroscopes to explore the properties of X-rays. His fluoroscopes used a layer of barium platinocyanide crystals coating the inside of a glass screen. These crystals would fluoresce (glow) when X-rays hit them and so show a shadow image of whatever was put between the X-ray source and screen. However, these early fluoroscopes produced only faint light and so faint X-ray images. After trying around 1300 compounds, Edison and his team discovered that calcium tungstate fluoresced 12,000 times more brightly than the barium platinocyanide that Roentgen had used. This led Edison to believe that he had found his fluorescent lamp (see Figure 2).

The difficulty of producing glass X-ray tubes, fluorescent lamps, and fluoroscopes meant that skilled glass blowers were crucial in the development of Edison’s ideas. Clarence Dally, and his brother Charles who later joined him, were put to work and Dally soon became fascinated. He took to the work enthusiastically using his glassblowing skills to produce thousands of different X-ray tube prototypes. Dally had to test each tube and fluoroscope many times by holding his hand between the X-ray source and a fluorescent screen, exposing him to huge doses of X-rays.

Thomas Edison photographed with his X-ray tube fluorescent lamp (arrow).
Figure 2: Thomas Edison photographed with his X-ray tube fluorescent lamp (arrow). [4]

Dally and his brother were essential to Edison’s work, particularly when the X-ray facilities were transported and manipulated during demonstrations. The first public demonstration of Edison’s new fluoroscope was at the National Electric Light Association held in New York City in May 1896. It was a sensation. It is difficult now to imagine the effect on the public of seeing their own bones for the very first time. Dally’s job was to keep the temperamental system running and this meant close and continued contact with the equipment, resulting in a level of exposure that caused Dally’s hair and moustache to fall out. It had not yet been noted that the damage caused by X-rays was cumulative and it was still assumed that the effects could be reversed with time away from the source.

Edison saw this research as a contribution to science and refused to patent the new screen, instead arranging for them to be manufactured and sold at modest prices for medical use [5]. However, as X-ray technology became more widely used, doctors found they preferred the more permanent photographic plate record for X-rays rather than the Edison’s fluoroscope. Photographic plates also meant a much lower dose of X-rays to the radiographer and patient.

Dally (arrow) undergoes fluoroscopy by Thomas Edison.
Figure 3: Dally (arrow) undergoes fluoroscopy by Thomas Edison. [4]

By 1900, Dally was suffering radiation damage to his hands and face. When his left hand became reddened, swollen, and extremely painful from testing the X-ray tubes, he just started to use his right. Eventually he was forced to periodically take time off work, only to return after the pain and swelling had subsided. Around this time Edison himself developed problems with his own eyesight and that convinced Edison that prolonged exposure to X-rays was dangerous. He stopped working with X-rays himself and also encouraged Dally to stop, but he would not. About his plans for using X-rays to produce a fluorescent lighting system Edison later admitted to the New York World, “I could make the lamp all right, but when I did so I found that it would kill everybody who would use it continuously.” [1]

Edison continued to pay Dally even when he could not work and paid for the best dermatologists and surgeons on the East Coast to attend to him. In 1902, one lesion on Dally’s left wrist was treated unsuccessfully with 144 skin grafts from his legs but the tissue was so badly damaged that the hand had to be amputated. An ulceration on his right hand necessitated the amputation of four fingers. Eventually, cancer caused by X-ray exposure had spread to such an extent that it became necessary to amputate both arms simultaneously. Even this major surgery was not sufficient to preserve Dally’s life and he died in October 1904.

Clarence M. Dally
Figure 4: Clarence M. Dally [6]

Dally was survived by a wife and two children. Dr W.B. Graves said of Dally, “He presents to science a pitiable object-lesson of the dangers of inexperienced or continuous experiments with X-rays, and his sufferings have done more to bring to professional notice a correct knowledge of things to be avoided than anything else in the history of scientific research upon this subject.”[1] However, to remember Dally solely as a tragic figure is to forget the contribution he made to the improvement of the X-ray tube and fluoroscope, which had a huge impact on the medical profession and saved many people’s lives.

Timeline of Clarence Dally's life
Timeline of Clarence Dally’s life


Clarence was not the only technician to suffer in the development of X-ray technology. Roentgen’s own technicians suffered major medical issues with their hands. This is shown in Figure 5. I have not been able to find out the name of this technician pictured – or the source of this image.

Rontgen assistants


[1] Edison Fears Hidden Perils of the X-rays, New York World, August 3, 1903, accessed from

[2] O. Glasser, William Conrad Roentgen and the early history of the roentgen rays. Springfield, IL: Thomas, 1934

[3] R.A. Gagliardi, Clarence Dally: An American Pioneer, American Journal of Roentgenology, 157:922, November 1991 p992

[4] D. J. DeSantis, Early American Radiology: The Pioneer Years, American Journal of Roentgenology, 147:850-853, October 1986. p.850-853.

[5] P. Israel, Edison: A life of invention, John Wiley & Sons, Inc., 1998.

[6] P. Brown, Clarence Madison Dally (1865-1904), American Martyrs to Radiology American Journal of Roentgenology, 1995;164, p237-239

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