prize8-5, Exercise 1: "Fresnel invented the lighthouse lens"

Model answer (check the details), using the six questions:

1. Who says it? Popular histories, lighthouse guides and museums, who often present a single inventor.
2. What exactly is claimed? That Fresnel invented the lens. "Invented" could mean the idea of a stepped lens, the optical design, or the first working lighthouse lens.
3. What would count as evidence? Descriptions of earlier proposals, patents and published papers, records of the first installations, and the opinion of historians of optics.
4. Compared with what? Earlier proposals for stepped lenses (Buffon in the 18th century, check) and earlier reflector systems.
5. Which period? The 18th century to the 1820s.
6. What would change my mind? Evidence of an earlier working lens in a lighthouse, or evidence that Fresnel's design was only a copy.

Verdict: Fresnel did not invent the idea of a stepped lens, which had been proposed before, but he worked out the optics, designed the combined system of rings and prisms and had it built and installed at Cordouan in 1823, so "invented the Fresnel lens" is true in that sense (check). A careful sentence: "Fresnel designed and introduced the compound lens system used in lighthouses, building on earlier ideas for stepped lenses."

Care: "first" and "invented" claims need a definition of what exactly was first.