instrument for measuring the transparency of air
• (n.) An instrument for measuring the transparency of the air.
Di`a·pha·nom'e·ter noun [ Greek ... transparent + -meter .] An instrument for measuring the transparency of the air. 
diaphanometer 1. An instrument for measuring the transparency of a solid, liquid, or gas. 2. An instrument for testing urine and other fluids by means of transmitted light.
an instrument for measuring the transparency of a solid, liquid, or gas.