This circular, faceted prism is fashioned from a perfect crystal of pale aquamarine. 

When held before the eye, it enables the user to sense radiation in the ultraviolet spectrum. In effect, the user is able to see in total darkness as if he or she were in bright moonlight. General outlines can be distinguished from up to 240 feet away, and details can be seen clearly for 120 feet distance. 

Of course, the device must be held so as to be able to look through it. 

A lens of ultravision is about 1½ inches in diameter.