In 1727, German anatomy professor Johann Heinrich Schulze proved that the darkening of silver salts was caused by light rather than heat, recording words on the salts with sunlight, though he did not preserve the images permanently.
Notes on verification
Confirmed by multiple independent sources including Britannica, Wikipedia, Camera Museum, and Encyclopedia.com. Minor discrepancy on exact experiment date vs. publication date (1727) does not undermine core claim.
Sources
- History of photography | History, Inventions, Artists, & Facts - Britannica (britannica.com)
- https://www.cameramuseum.ch/en/discover/permanent-exhibition/the-origins-of-photography/the-precursors-johann-heinrich-schulze/ (cameramuseum.ch)
- https://silverhalloffame.com/bios/johann-heinrich-schulze/ (silverhalloffame.com)