Crossword clue: an optical glass that is convex on both sides. hutton.
2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).
Possible answers
An optical glass that is convex on both sides. [Obs.] Hutton.
An optical glass that is convex on both sides. [Obs.] Hutton.