Roentgen

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Wilhelm Roentgen was 50; head of Physics at the University of Wurzburg; author of many books. Late one Friday evening he wrapped a Crooke's tube in black card to mask the light from the fluorescence of the glass walls. He turned the tube off, then on again. The cardboard trapped all the visible light. By chance, a screen coated with barium platinocyanide (a fluorescent material used at the time to develop photographic plates) lay on a chair a few feet away. He noticed a soft glow (He could not see it was green because he was colorblind). A faint letter A appeared on the screen. A student had used a finger to write A on the liquid barium platinocyanide. Roentgen turned off the tube. The 'A' disappeared. He turned it on again. The A reappeared. Rays were passing through the black card.

He made shadow pictures of coins in a purse and of of his wife's hand. Bertha Roentgen was appalled by the deathlike appearance of her hand. She never went near her husband's experiments again. Very wise.