X rays

"X rays," also known as "Röntgen rays," were discovered only eight or nine years before the time represented in Ulysses. They seized the imagination of ordinary people like Bloom, whose thoughts on the subject seem more than usually fuzzy.

JH 2018

Radiograph of Albert von Kölliker's left hand, taken at a public lecture by Röntgen in January 1896. Source: Wikimedia Commons.

Photograph of hands being x-rayed in the 1890s, published in William J. Morton and Edwin W.  Hammer's The X-ray, or, Photography of the Invisible (1896). Source: Wikimedia Commons.