One winter's day, when it snowed, he brought out a burning-glass, then he held out the tail of his blue coat, and let the snow-flakes fall upon it. "Look in this glass, Gerda," said he; and she saw how every flake of snow was magnified, and looked like a beautiful flower or a glittering star.
Source: tatoeba (3753010)
The more he sees her, the worse he is, uritque videndo; as in a burning-glass the sunbeams are re-collected to a centre, the rays of love are projected from her eyes.
Source: wiktionary
Our burning-glass also now became a great treasure, as it enabled me to magnify, and so perceive more clearly […].
Source: wiktionary
The Vestal fire was rekindled by sunlight reflected from a burning-glass.
Source: wiktionary