Wiktionary
burning-glass
n. (context dated English) A magnifying lens, as used to focus sunlight on to an object.
Usage examples of "burning-glass".
At my laboratory the possibility can be demonstrated using a burning-glass and a block of white rock half-covered with soot.
I've got a scar where some young fool shone a burning-glass on my mantle when I was a budling.
Using a burning-glass is something else, because we assume the sun to be made of fire fiercer than what we can imitate down here.
He had his burning-glass in his pocket, he’d some wrapped, waxed matches on him, but he was scared to do it for fear that Harper or a horse he didn’t want to meet or even think about would smell it on the wind, in this place where smells you didn’t notice downland were very, very obvious as man-made.