Scientist whose "number" is a dimensionless ratio (4)

I believe the answer is:

mach

(Other definitions for mach that I've seen before include "Ratio used to measure high speeds" , "-- Number relates to speeds" , "Ratio of a body's speed to the speed of sound" , "Number referring to speed of sound" , "The speed of sound is ... one" .)

I've seen this clue in The New York Times.

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