On November 8, 1895 William Roentgen accidentally discovered a new kind of radiation. He was testing cathode rays to see if they would pass through glass when he noticed a glow emanating from a chemically coated screen lying a few feet away. Roentgen named the unknown rays that caused this fluorescence "X rays." Working intensely in seclusion for two months, he found that X rays could penetrate some substances but not others. During one experiment, Roentgen tested the X-ray absorption of lead. While holding a lead disk up to the source of radiation, he inadvertently exposed his hand to the rays. The resulting shadows on the detecting screen revealed both the impenetrability of lead and the bones in his hand. Roentgen had discovered that X rays penetrate human flesh, but not bone.

Roentgen was also the first to discover that X rays could be captured by photography. Reasoning that X rays were like light, he placed the hand of his wife, Bertha, on a photographic plate and exposed it to his X-ray source. When the plate was developed, the bones in her hand and her rings were clearly visible. Many copies of this photograph have been produced; one is on display in the Museum.

6. Examining chair, circa 1910.