Austin Hall 
The Man Who Saved The Earth [EPUB ebook] 

The story opens on an oppressively hot day with a poor little newspaper boy, Charley, playing with a "burning glass" (a magnifying glass) which he uses to concentrate sunlight onto a small focal spot, thus intensifying the heat on some paper until it burns a hole, perhaps a portent of things to come. He is noticed by a recluse scientist, Dr. Robold, who takes interest in Charley's scientific curiosity and calls him a young Archimedes