Function: noun
Date: 1839
: the ratio of the speed of radiation (as light) in one medium (as air, glass, or a vacuum) to that in another medium
Function: noun
Date: 1839
: the ratio of the speed of radiation (as light) in one medium (as air, glass, or a vacuum) to that in another medium
Merriam Webster Collegiate English Dictionary. Merriam Webster - Энциклопедический словарь английского языка. 2012