1. 
   Burning glass
   A burning glass or burning lens is a large convex lens that can concentrate the sun`s rays onto a small area, heating up the area and thus resulting in ignition of the exposed surface. Burning mirrors achieve a similar effect by using reflecting surfaces to focus the light. They were used in 18th-c...
   Found op http://en.wikipedia.org/wiki/Burning_glass
   
   
2. 
   Burning-Glass
   A burning-glass is a lens which, by bringing the sun's rays rapidly to a focus, produces a heat strong enough to kindle combustible matter.
   Found op http://www.probertencyclopaedia.com/browse/GB.HTM
   
   

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