Before November 1895: physicists including Johann Wilhelm Hittorf, William Crookes and Philipp Lenard had developed and studied electrical discharges in evacuated glass tubes and the behaviour of cathode rays. Some apparatus produced X-rays and some photographic plates were affected before Röntgen's work, but the effect was not recognised as a distinct radiation. Uwe Busch's study of later priority claims therefore distinguishes unknowingly producing an effect from identifying, investigating and publishing it.
8 November–22 December 1895: 8 November is the conventionally accepted date on which Röntgen noticed fluorescence outside a covered tube at the University of Würzburg. He then tested penetration through materials, effects on fluorescent screens and photographic plates, and whether the rays could be reflected, refracted or deflected. The University of Würzburg's exhibition catalogue dates the hand exposure to 22 December. Published accounts give differing exposure estimates, so an exact duration should not be inferred from the print.
28 December 1895: Röntgen submitted Ueber eine neue Art von Strahlen (“On a New Kind of Rays”) to the Würzburg Physico-Medical Society. It was a preliminary physical report, organised as seventeen numbered observations rather than a medical case study. It noted that a hand on a fluorescent screen showed dark bone shadows within fainter tissue and that photographic plates could register the rays. The hand photograph illustrated those claims when prints circulated with offprints; it was not printed inside the first pamphlet.
1–23 January 1896: Röntgen mailed offprints and, to a smaller group, sets of positive prints. Frans Zonneveld's study of a set sent to Hendrik Lorentz identifies nine images and shows how the hand print functioned beside technical studies of a doorpost, wire, metal and enclosed objects. A newspaper report appeared in Vienna on 5 January; Arthur Stanton's English translation appeared in Nature on 23 January. Replication depended not just on publicity but on existing international networks of physicists, instrument makers, photographers and medical practitioners.